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  • SSH service will not start on fresh Cygwin 1.7.15 install

    - by Coder6841
    OS: Windows 7 x64 Cygwin: 1.7.15-1 OpenSSH: 6.0p1-1 I'm attempting to install an SSH server on Windows 7. The tutorial that I'm following to do this is here: http://www.howtogeek.com/howto/41560/how-to-get-ssh-command-line-access-to-windows-7-using-cygwin/ The issue is that upon executing the net start sshd command I get the following output:The CYGWIN sshd service is starting. The CYGWIN sshd service could not be started. The service did not report an error. More help is available by typing NET HELPMSG 3534. Here is the full output of the setup: AdminUser@ThisComputer ~ $ ssh-host-config *** Info: Generating /etc/ssh_host_key *** Info: Generating /etc/ssh_host_rsa_key *** Info: Generating /etc/ssh_host_dsa_key *** Info: Generating /etc/ssh_host_ecdsa_key *** Info: Creating default /etc/ssh_config file *** Info: Creating default /etc/sshd_config file *** Info: Privilege separation is set to yes by default since OpenSSH 3.3. *** Info: However, this requires a non-privileged account called 'sshd'. *** Info: For more info on privilege separation read /usr/share/doc/openssh/README.privsep. *** Query: Should privilege separation be used? (yes/no) yes *** Info: Note that creating a new user requires that the current account have *** Info: Administrator privileges. Should this script attempt to create a *** Query: new local account 'sshd'? (yes/no) yes *** Info: Updating /etc/sshd_config file *** Query: Do you want to install sshd as a service? *** Query: (Say "no" if it is already installed as a service) (yes/no) yes *** Query: Enter the value of CYGWIN for the daemon: [] *** Info: On Windows Server 2003, Windows Vista, and above, the *** Info: SYSTEM account cannot setuid to other users -- a capability *** Info: sshd requires. You need to have or to create a privileged *** Info: account. This script will help you do so. *** Info: You appear to be running Windows XP 64bit, Windows 2003 Server, *** Info: or later. On these systems, it's not possible to use the LocalSystem *** Info: account for services that can change the user id without an *** Info: explicit password (such as passwordless logins [e.g. public key *** Info: authentication] via sshd). *** Info: If you want to enable that functionality, it's required to create *** Info: a new account with special privileges (unless a similar account *** Info: already exists). This account is then used to run these special *** Info: servers. *** Info: Note that creating a new user requires that the current account *** Info: have Administrator privileges itself. *** Info: No privileged account could be found. *** Info: This script plans to use 'cyg_server'. *** Info: 'cyg_server' will only be used by registered services. *** Query: Do you want to use a different name? (yes/no) no *** Query: Create new privileged user account 'cyg_server'? (yes/no) yes *** Info: Please enter a password for new user cyg_server. Please be sure *** Info: that this password matches the password rules given on your system. *** Info: Entering no password will exit the configuration. *** Query: Please enter the password: *** Query: Reenter: *** Info: User 'cyg_server' has been created with password '[CENSORED]'. *** Info: If you change the password, please remember also to change the *** Info: password for the installed services which use (or will soon use) *** Info: the 'cyg_server' account. *** Info: Also keep in mind that the user 'cyg_server' needs read permissions *** Info: on all users' relevant files for the services running as 'cyg_server'. *** Info: In particular, for the sshd server all users' .ssh/authorized_keys *** Info: files must have appropriate permissions to allow public key *** Info: authentication. (Re-)running ssh-user-config for each user will set *** Info: these permissions correctly. [Similar restrictions apply, for *** Info: instance, for .rhosts files if the rshd server is running, etc]. *** Info: The sshd service has been installed under the 'cyg_server' *** Info: account. To start the service now, call `net start sshd' or *** Info: `cygrunsrv -S sshd'. Otherwise, it will start automatically *** Info: after the next reboot. *** Info: Host configuration finished. Have fun! AdminUser@ThisComputer ~ $ net start sshd The CYGWIN sshd service is starting. The CYGWIN sshd service could not be started. The service did not report an error. More help is available by typing NET HELPMSG 3534. Note that on the line *** Query: Enter the value of CYGWIN for the daemon: [] I haven't entered anything. Tutorials often say to use ntsec or ntsec tty here but those options are removed from the latest version of OpenSSH. I've tried using them anyway and the result is the same. The file /var/log/sshd.log is empty. If I try just running the command /usr/sbin/sshd I get the output /var/empty must be owned by root and not group or world-writable.. The /var/empty directory has the following permissions: drwxr-xr-x+ 1 cyg_server root 0 May 29 15:28 empty. Google searches on this error did not turn up any working fixes. One person seems to have solved it by using the command chown SYSTEM /var/empty but that did not fix it in my case.

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  • The curious case of SOA Human tasks' automatic completion

    - by Kavitha Srinivasan
    A large south-Asian insurance industry customer using Oracle BPM and SOA ran into this. I have survived this ordeal previously myself but didnt think to blog it then. However, it seems like a good idea to share this knowledge with this reader community and so here goes.. Symptom: A human task (in a SOA/BPEL/BPM process) completes automatically while it should have been assigned to a proper user.There are no stack traces, no related exceptions in the logs. Why: The product is designed to treat human tasks that don't have assignees as one that is eligible for completion. And hence no warning/error messages are recorded in the logs. Usecase variant: A variant of this usecase, where an assignee doesnt exist in the repository is treated as a recoverable error. One can find this in the 'pending recovery' instances in EM and reactivate the task by changing the assignees in the bpm workspace as a process owner /administrator. But back to the usecase when tasks get completed automatically... When: This happens when the users/groups assigned to a task are 'empty' or null. This has been seen only on tasks whose assignees are derived from an assignment expression - ie at runtime an XPath is used to determine who to assign the task to. (This should not happen if task assignees are populated via swim-lane roles.) How to detect this in EM For instances that are auto-completed thus, one will notice in the Audit Trail of such instances, that the 'outcome' of the task is empty. The 'acquired by' element will also show as empty/null. Enabling the oracle.soa.services.workflow.* logger in em should print more verbose messages about this. How to fix this The application code needs two fixes: input to HT: The XSLT/XPath used  to set the task 'assignee' and the process itself should be enhanced to handle nulls better. For eg: if no-data-found, set assignees to alternate value, force default assignees etc. output from HT: Additionally, in the application code, check that the 'outcome' of the HT is not-null. If null, route the task to be performed again after setting the assignee correctly. Beginning PS4FP, one should be able to use 'grab' to route back to the task to fire again. Hope this helps. 

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  • July, the 31 Days of SQL Server DMO’s – Day 24 (sys.dm_db_index_operational_stats)

    - by Tamarick Hill
    The sys.dm_db_index_operational_stats Dynamic Management Function returns information about the IO, locking, and access methods for the indexes that you currently have on your SQL Server Instance. This function takes four input parameters which are (1) database_id, (2) object_id, (3) index_id, and (4) partition_number. Let’s have a look at the results from this function against our AdventureWorks2012 database. This function returns a ton of columns, so not only will I not attempt to describe each of the columns, I wont even attempt to display all of them here. My query below will give you a subset of the columns returned from this function. SELECT database_id, object_id, index_id, partition_number, leaf_insert_count, leaf_delete_count, leaf_update_count, leaf_ghost_count, nonleaf_insert_count, nonleaf_delete_count, nonleaf_update_count, range_scan_count, forwarded_fetch_count, row_lock_count, row_lock_wait_count, page_lock_count, page_lock_wait_count, Index_lock_promotion_attempt_count, index_lock_promotion_count, page_compression_attempt_count, page_compression_success_count FROM sys.dm_db_index_operational_stats(db_id('AdventureWorks2012'), NULL, NULL, NULL) The first four columns in the result set represent the values that we passed in as our input parameters. If you use NULL’s as I did, then you will see results for every index on your system. I specified a database_id so my result set only shows those records pertaining to my AdventureWorks2012 database. The next columns in the result set provide you with information on how may inserts, deletes, or updates that have taken place on your leaf and nonleaf index levels. The nonleaf levels would refer to the intermediate and root index levels. In the middle of these you see a leaf_ghost_count column, which represents the number of records that have been logically deleted and marked as “ghosted”  and are waiting on the background ghost cleanup process to physically remove them. The range_scan_count column represents the number of range or table scans that have been performed against an index. The forwarded_fetch_count column represents the number of rows that were returned from a forwarding row pointer. The row_lock_count and row_lock_wait_count represent the number of row locks that have been requested for an index and the number of times SQL has had to wait on a row lock respectively. The page_lock_count and page_lock_wait_count represent the number of page locks that have been requested for an index and the number of times SQL has had to wait on a page lock respectively. The index_lock_promotion_attempt_count represents the number of times the database engine has attempted to promote a lock to the index level. The index_lock_promotion_count column displays how many times that index lock promotion was successful. Lastly the page_compression_attempt_count and page_compression_success_count represents how many times a page was attempted to be compressed and how many times the attempt was successful. As you can see there is a ton of information returned from this DMV. The DMV we reviewed on yesterday (sys.dm_db_index_usage_stats) provided you with good information on when and how indexes have been used, but this DMF takes an even deeper dive into these statistics. If you are interested in performing a very detailed analysis on the operational stats of your indexes, this is not only a good place to start, but more than likely the best place. For more information on this Dynamic Management Function, please see the below Books Online link: http://msdn.microsoft.com/en-us/library/ms174281.aspx Follow me on Twitter @PrimeTimeDBA

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  • BAM design pointers

    - by Kavitha Srinivasan
    In working recently with a large Oracle customer on SOA and BAM, I discovered that some BAM best practices are not quite well known as I had always assumed ! There is a doc bug out to formally incorporate those learnings but here are a few notes..  EMS-DO parity When using EMS (Enterprise Message Source) as a BAM feed, the best practice is to use one EMS to write to one Data Object. There is a possibility of collisions and duplicates when multiple EMS write to the same row of a DO at the same time. This customer had 17 EMS writing to one DO at the same time. Every sensor in their BPEL process writes to one topic but the Topic was read by 1 EMS corresponding to one sensor. They then used XSL within BAM to transform the payload into the BAM DO format. And hence for a given BPEL instance, 17 sensors fired, populated 1 JMS topic, was consumed by 17 EMS which in turn wrote to 1 DataObject.(You can image what would happen for later versions of the application that needs to send more information to BAM !).  We modified their design to use one Master XSL based on sensorname for all sensors relating to a DO- say Data Object 'Orders' and were able to thus reduce the 17 EMS to 1 with a master XSL. For those of you wondering about how squeaky clean this design is, you are right ! This is indeed not squeaky clean and that brings us to yet another 'inferred' best practice. (I try very hard not to state the obvious in my blogs with the hope that everytime I blog, it is very useful but this one is an exception.) Transformations and Calculations It is optimal to do transformations within an engine like BPEL. Not only does this provide modelling ease with a nice GUI XSL mapper in JDeveloper, the XSL engine in BPEL is quite efficient at runtime as well. And so, doing XSL transformations in BAM is not quite prudent.  The same is true for any non-trivial calculations as well. It is best to do all transformations,calcuations and sanitize the data in a BPEL or like layer and then send this to BAM (via JMS, WS etc.) This then delegates simply the function of report rendering and mechanics of real-time reporting to the Oracle BAM reporting tool which it is most suited to do. All nulls are not created equal Here is yet another possibly known fact but reiterated here. For an EMS with an Upsert operation: a) If Empty tags or tags with no value are sent like <Tag1/> or <Tag1></Tag1>, the DO will be overwritten with --null-- b) If Empty tags are suppressed ie not generated at all, the corresponding DO field will NOT be overwritten. The field will have whatever value existed previously.  For an EMS with an Insert operation, both tags with an empty value and no tags result in –null-- being written to the DO. Hope this helps .. Happy 4th!

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  • Microsoft MVP for the year 2011

    - by vik20000in
    It’s been three year in a row now. I am MVP for the year 2011 also. It feels so great to get the news that I have been MVP again. Very big thanks to the MVP Team, My MVP Lead and Microsoft for giving the MVP award to me for 3 year in a row. Also a great thanks to all the friends, Family, developers, community members that have worked with me. Without your support this would not have been possible. I will try and continue the work in 2011 alsoVikram

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  • How do I make my purchased music be synchronized on Rhythmbox and in ~./ubuntuone/Purchased from Ubuntu One?

    - by dln9
    I am signed up for the Ubuntu One service, and have my computer added. Under System ? Preferences ? Ubuntu One, I have enabled all synchronizations, including for music. System ? Prefereneces ? Ubuntu One, it shows this message: "Synchronization Complete". But, when (via Rhythmbox) I purchase a song, no synchronization occurs. I can see the purchased song on the Ubuntu One web page, but the "Purchased Music" folder in Rhythmbox is empty, and the folder ~/.ubuntuone/Purchased from Ubuntu One is also empty. (So, the only way I can get at the song is to manually download it from the Ubuntu One web site to my computer.) I thought that these synchronizations should just happen automatically, but it appears that is not the case for me, and I can't figure out why. Thanks in advance for any help.

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  • SQL SERVER – Introduction to FIRST _VALUE and LAST_VALUE – Analytic Functions Introduced in SQL Server 2012

    - by pinaldave
    SQL Server 2012 introduces new analytical functions FIRST_VALUE() and LAST_VALUE(). This function returns first and last value from the list. It will be very difficult to explain this in words so I’d like to attempt to explain its function through a brief example. Instead of creating a new table, I will be using the AdventureWorks sample database as most developers use that for experiment purposes. Now let’s have fun following query: USE AdventureWorks GO SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty, FIRST_VALUE(SalesOrderDetailID) OVER (ORDER BY SalesOrderDetailID) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (ORDER BY SalesOrderDetailID) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty GO The above query will give us the following result: What’s the most interesting thing here is that as we go from row 1 to row 10, the value of the FIRST_VALUE() remains the same but the value of the LAST_VALUE is increasing. The reason behind this is that as we progress in every line – considering that line and all the other lines before it, the last value will be of the row where we are currently looking at. To fully understand this statement, see the following figure: This may be useful in some cases; but not always. However, when we use the same thing with PARTITION BY, the same query starts showing the result which can be easily used in analytical algorithms and needs. Let us have fun through the following query: Let us fun following query. USE AdventureWorks GO SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty, FIRST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty GO The above query will give us the following result: Let us understand how PARTITION BY windows the resultset. I have used PARTITION BY SalesOrderID in my query. This will create small windows of the resultset from the original resultset and will follow the logic or FIRST_VALUE and LAST_VALUE in this resultset. Well, this is just an introduction to these functions. In the future blog posts we will go deeper to discuss the usage of these two functions. By the way, these functions can be applied over VARCHAR fields as well and are not limited to the numeric field only. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • How to nest transactions nicely - &quot;begin transaction&quot; vs &quot;save transaction&quot; and SQL Server

    - by Brian Biales
    Do you write stored procedures that might be used by others?  And those others may or may not have already started a transaction?  And your SP does several things, but if any of them fail, you have to undo them all and return with a code indicating it failed? Well, I have written such code, and it wasn’t working right until I finally figured out how to handle the case when we are already in a transaction, as well as the case where the caller did not start a transaction.  When a problem occurred, my “ROLLBACK TRANSACTION” would roll back not just my nested transaction, but the caller’s transaction as well.  So when I tested the procedure stand-alone, it seemed to work fine, but when others used it, it would cause a problem if it had to rollback.  When something went wrong in my procedure, their entire transaction was rolled back.  This was not appreciated. Now, I knew one could "nest" transactions, but the technical documentation was very confusing.  And I still have not found the approach below documented anywhere.  So here is a very brief description of how I got it to work, I hope you find this helpful. My example is a stored procedure that must figure out on its own if the caller has started a transaction or not.  This can be done in SQL Server by checking the @@TRANCOUNT value.  If no BEGIN TRANSACTION has occurred yet, this will have a value of 0.  Any number greater than zero means that a transaction is in progress.  If there is no current transaction, my SP begins a transaction. But if a transaction is already in progress, my SP uses SAVE TRANSACTION and gives it a name.  SAVE TRANSACTION creates a “save point”.  Note that creating a save point has no effect on @@TRANCOUNT.  So my SP starts with something like this: DECLARE @startingTranCount int SET @startingTranCount = @@TRANCOUNT IF @startingTranCount > 0 SAVE TRANSACTION mySavePointName ELSE BEGIN TRANSACTION -- … Then, when ready to commit the changes, you only need to commit if we started the transaction ourselves: IF @startingTranCount = 0 COMMIT TRANSACTION And finally, to roll back just your changes so far: -- Roll back changes... IF @startingTranCount > 0 ROLLBACK TRANSACTION MySavePointName ELSE ROLLBACK TRANSACTION Here is some code that you can try that will demonstrate how the save points work inside a transaction. This sample code creates a temporary table, then executes selects and updates, documenting what is going on, then deletes the temporary table. if running in SQL Management Studio, set Query Results to: Text for best readability of the results. -- Create a temporary table to test with, we'll drop it at the end. CREATE TABLE #ATable( [Column_A] [varchar](5) NULL ) ON [PRIMARY] GO SET NOCOUNT ON -- Ensure just one row - delete all rows, add one DELETE #ATable -- Insert just one row INSERT INTO #ATable VALUES('000') SELECT 'Before TRANSACTION starts, value in table is: ' AS Note, * FROM #ATable SELECT @@trancount AS CurrentTrancount --insert into a values ('abc') UPDATE #ATable SET Column_A = 'abc' SELECT 'UPDATED without a TRANSACTION, value in table is: ' AS Note, * FROM #ATable BEGIN TRANSACTION SELECT 'BEGIN TRANSACTION, trancount is now ' AS Note, @@TRANCOUNT AS TranCount UPDATE #ATable SET Column_A = '123' SELECT 'Row updated inside TRANSACTION, value in table is: ' AS Note, * FROM #ATable SAVE TRANSACTION MySavepoint SELECT 'Save point MySavepoint created, transaction count now:' as Note, @@TRANCOUNT AS TranCount UPDATE #ATable SET Column_A = '456' SELECT 'Updated after MySavepoint created, value in table is: ' AS Note, * FROM #ATable SAVE TRANSACTION point2 SELECT 'Save point point2 created, transaction count now:' as Note, @@TRANCOUNT AS TranCount UPDATE #ATable SET Column_A = '789' SELECT 'Updated after point2 savepoint created, value in table is: ' AS Note, * FROM #ATable ROLLBACK TRANSACTION point2 SELECT 'Just rolled back savepoint "point2", value in table is: ' AS Note, * FROM #ATable ROLLBACK TRANSACTION MySavepoint SELECT 'Just rolled back savepoint "MySavepoint", value in table is: ' AS Note, * FROM #ATable SELECT 'Both save points were rolled back, transaction count still:' as Note, @@TRANCOUNT AS TranCount ROLLBACK TRANSACTION SELECT 'Just rolled back the entire transaction..., value in table is: ' AS Note, * FROM #ATable DROP TABLE #ATable The output should look like this: Note                                           Column_A ---------------------------------------------- -------- Before TRANSACTION starts, value in table is:  000 CurrentTrancount ---------------- 0 Note                                               Column_A -------------------------------------------------- -------- UPDATED without a TRANSACTION, value in table is:  abc Note                                 TranCount ------------------------------------ ----------- BEGIN TRANSACTION, trancount is now  1 Note                                                Column_A --------------------------------------------------- -------- Row updated inside TRANSACTION, value in table is:  123 Note                                                   TranCount ------------------------------------------------------ ----------- Save point MySavepoint created, transaction count now: 1 Note                                                   Column_A ------------------------------------------------------ -------- Updated after MySavepoint created, value in table is:  456 Note                                              TranCount ------------------------------------------------- ----------- Save point point2 created, transaction count now: 1 Note                                                        Column_A ----------------------------------------------------------- -------- Updated after point2 savepoint created, value in table is:  789 Note                                                     Column_A -------------------------------------------------------- -------- Just rolled back savepoint "point2", value in table is:  456 Note                                                          Column_A ------------------------------------------------------------- -------- Just rolled back savepoint "MySavepoint", value in table is:  123 Note                                                        TranCount ----------------------------------------------------------- ----------- Both save points were rolled back, transaction count still: 1 Note                                                            Column_A --------------------------------------------------------------- -------- Just rolled back the entire transaction..., value in table is:  abc

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  • PTLQueue : a scalable bounded-capacity MPMC queue

    - by Dave
    Title: Fast concurrent MPMC queue -- I've used the following concurrent queue algorithm enough that it warrants a blog entry. I'll sketch out the design of a fast and scalable multiple-producer multiple-consumer (MPSC) concurrent queue called PTLQueue. The queue has bounded capacity and is implemented via a circular array. Bounded capacity can be a useful property if there's a mismatch between producer rates and consumer rates where an unbounded queue might otherwise result in excessive memory consumption by virtue of the container nodes that -- in some queue implementations -- are used to hold values. A bounded-capacity queue can provide flow control between components. Beware, however, that bounded collections can also result in resource deadlock if abused. The put() and take() operators are partial and wait for the collection to become non-full or non-empty, respectively. Put() and take() do not allocate memory, and are not vulnerable to the ABA pathologies. The PTLQueue algorithm can be implemented equally well in C/C++ and Java. Partial operators are often more convenient than total methods. In many use cases if the preconditions aren't met, there's nothing else useful the thread can do, so it may as well wait via a partial method. An exception is in the case of work-stealing queues where a thief might scan a set of queues from which it could potentially steal. Total methods return ASAP with a success-failure indication. (It's tempting to describe a queue or API as blocking or non-blocking instead of partial or total, but non-blocking is already an overloaded concurrency term. Perhaps waiting/non-waiting or patient/impatient might be better terms). It's also trivial to construct partial operators by busy-waiting via total operators, but such constructs may be less efficient than an operator explicitly and intentionally designed to wait. A PTLQueue instance contains an array of slots, where each slot has volatile Turn and MailBox fields. The array has power-of-two length allowing mod/div operations to be replaced by masking. We assume sensible padding and alignment to reduce the impact of false sharing. (On x86 I recommend 128-byte alignment and padding because of the adjacent-sector prefetch facility). Each queue also has PutCursor and TakeCursor cursor variables, each of which should be sequestered as the sole occupant of a cache line or sector. You can opt to use 64-bit integers if concerned about wrap-around aliasing in the cursor variables. Put(null) is considered illegal, but the caller or implementation can easily check for and convert null to a distinguished non-null proxy value if null happens to be a value you'd like to pass. Take() will accordingly convert the proxy value back to null. An advantage of PTLQueue is that you can use atomic fetch-and-increment for the partial methods. We initialize each slot at index I with (Turn=I, MailBox=null). Both cursors are initially 0. All shared variables are considered "volatile" and atomics such as CAS and AtomicFetchAndIncrement are presumed to have bidirectional fence semantics. Finally T is the templated type. I've sketched out a total tryTake() method below that allows the caller to poll the queue. tryPut() has an analogous construction. Zebra stripping : alternating row colors for nice-looking code listings. See also google code "prettify" : https://code.google.com/p/google-code-prettify/ Prettify is a javascript module that yields the HTML/CSS/JS equivalent of pretty-print. -- pre:nth-child(odd) { background-color:#ff0000; } pre:nth-child(even) { background-color:#0000ff; } border-left: 11px solid #ccc; margin: 1.7em 0 1.7em 0.3em; background-color:#BFB; font-size:12px; line-height:65%; " // PTLQueue : Put(v) : // producer : partial method - waits as necessary assert v != null assert Mask = 1 && (Mask & (Mask+1)) == 0 // Document invariants // doorway step // Obtain a sequence number -- ticket // As a practical concern the ticket value is temporally unique // The ticket also identifies and selects a slot auto tkt = AtomicFetchIncrement (&PutCursor, 1) slot * s = &Slots[tkt & Mask] // waiting phase : // wait for slot's generation to match the tkt value assigned to this put() invocation. // The "generation" is implicitly encoded as the upper bits in the cursor // above those used to specify the index : tkt div (Mask+1) // The generation serves as an epoch number to identify a cohort of threads // accessing disjoint slots while s-Turn != tkt : Pause assert s-MailBox == null s-MailBox = v // deposit and pass message Take() : // consumer : partial method - waits as necessary auto tkt = AtomicFetchIncrement (&TakeCursor,1) slot * s = &Slots[tkt & Mask] // 2-stage waiting : // First wait for turn for our generation // Acquire exclusive "take" access to slot's MailBox field // Then wait for the slot to become occupied while s-Turn != tkt : Pause // Concurrency in this section of code is now reduced to just 1 producer thread // vs 1 consumer thread. // For a given queue and slot, there will be most one Take() operation running // in this section. // Consumer waits for producer to arrive and make slot non-empty // Extract message; clear mailbox; advance Turn indicator // We have an obvious happens-before relation : // Put(m) happens-before corresponding Take() that returns that same "m" for T v = s-MailBox if v != null : s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 // unlock slot to admit next producer and consumer return v Pause tryTake() : // total method - returns ASAP with failure indication for auto tkt = TakeCursor slot * s = &Slots[tkt & Mask] if s-Turn != tkt : return null T v = s-MailBox // presumptive return value if v == null : return null // ratify tkt and v values and commit by advancing cursor if CAS (&TakeCursor, tkt, tkt+1) != tkt : continue s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 return v The basic idea derives from the Partitioned Ticket Lock "PTL" (US20120240126-A1) and the MultiLane Concurrent Bag (US8689237). The latter is essentially a circular ring-buffer where the elements themselves are queues or concurrent collections. You can think of the PTLQueue as a partitioned ticket lock "PTL" augmented to pass values from lock to unlock via the slots. Alternatively, you could conceptualize of PTLQueue as a degenerate MultiLane bag where each slot or "lane" consists of a simple single-word MailBox instead of a general queue. Each lane in PTLQueue also has a private Turn field which acts like the Turn (Grant) variables found in PTL. Turn enforces strict FIFO ordering and restricts concurrency on the slot mailbox field to at most one simultaneous put() and take() operation. PTL uses a single "ticket" variable and per-slot Turn (grant) fields while MultiLane has distinct PutCursor and TakeCursor cursors and abstract per-slot sub-queues. Both PTL and MultiLane advance their cursor and ticket variables with atomic fetch-and-increment. PTLQueue borrows from both PTL and MultiLane and has distinct put and take cursors and per-slot Turn fields. Instead of a per-slot queues, PTLQueue uses a simple single-word MailBox field. PutCursor and TakeCursor act like a pair of ticket locks, conferring "put" and "take" access to a given slot. PutCursor, for instance, assigns an incoming put() request to a slot and serves as a PTL "Ticket" to acquire "put" permission to that slot's MailBox field. To better explain the operation of PTLQueue we deconstruct the operation of put() and take() as follows. Put() first increments PutCursor obtaining a new unique ticket. That ticket value also identifies a slot. Put() next waits for that slot's Turn field to match that ticket value. This is tantamount to using a PTL to acquire "put" permission on the slot's MailBox field. Finally, having obtained exclusive "put" permission on the slot, put() stores the message value into the slot's MailBox. Take() similarly advances TakeCursor, identifying a slot, and then acquires and secures "take" permission on a slot by waiting for Turn. Take() then waits for the slot's MailBox to become non-empty, extracts the message, and clears MailBox. Finally, take() advances the slot's Turn field, which releases both "put" and "take" access to the slot's MailBox. Note the asymmetry : put() acquires "put" access to the slot, but take() releases that lock. At any given time, for a given slot in a PTLQueue, at most one thread has "put" access and at most one thread has "take" access. This restricts concurrency from general MPMC to 1-vs-1. We have 2 ticket locks -- one for put() and one for take() -- each with its own "ticket" variable in the form of the corresponding cursor, but they share a single "Grant" egress variable in the form of the slot's Turn variable. Advancing the PutCursor, for instance, serves two purposes. First, we obtain a unique ticket which identifies a slot. Second, incrementing the cursor is the doorway protocol step to acquire the per-slot mutual exclusion "put" lock. The cursors and operations to increment those cursors serve double-duty : slot-selection and ticket assignment for locking the slot's MailBox field. At any given time a slot MailBox field can be in one of the following states: empty with no pending operations -- neutral state; empty with one or more waiting take() operations pending -- deficit; occupied with no pending operations; occupied with one or more waiting put() operations -- surplus; empty with a pending put() or pending put() and take() operations -- transitional; or occupied with a pending take() or pending put() and take() operations -- transitional. The partial put() and take() operators can be implemented with an atomic fetch-and-increment operation, which may confer a performance advantage over a CAS-based loop. In addition we have independent PutCursor and TakeCursor cursors. Critically, a put() operation modifies PutCursor but does not access the TakeCursor and a take() operation modifies the TakeCursor cursor but does not access the PutCursor. This acts to reduce coherence traffic relative to some other queue designs. It's worth noting that slow threads or obstruction in one slot (or "lane") does not impede or obstruct operations in other slots -- this gives us some degree of obstruction isolation. PTLQueue is not lock-free, however. The implementation above is expressed with polite busy-waiting (Pause) but it's trivial to implement per-slot parking and unparking to deschedule waiting threads. It's also easy to convert the queue to a more general deque by replacing the PutCursor and TakeCursor cursors with Left/Front and Right/Back cursors that can move either direction. Specifically, to push and pop from the "left" side of the deque we would decrement and increment the Left cursor, respectively, and to push and pop from the "right" side of the deque we would increment and decrement the Right cursor, respectively. We used a variation of PTLQueue for message passing in our recent OPODIS 2013 paper. ul { list-style:none; padding-left:0; padding:0; margin:0; margin-left:0; } ul#myTagID { padding: 0px; margin: 0px; list-style:none; margin-left:0;} -- -- There's quite a bit of related literature in this area. I'll call out a few relevant references: Wilson's NYU Courant Institute UltraComputer dissertation from 1988 is classic and the canonical starting point : Operating System Data Structures for Shared-Memory MIMD Machines with Fetch-and-Add. Regarding provenance and priority, I think PTLQueue or queues effectively equivalent to PTLQueue have been independently rediscovered a number of times. See CB-Queue and BNPBV, below, for instance. But Wilson's dissertation anticipates the basic idea and seems to predate all the others. Gottlieb et al : Basic Techniques for the Efficient Coordination of Very Large Numbers of Cooperating Sequential Processors Orozco et al : CB-Queue in Toward high-throughput algorithms on many-core architectures which appeared in TACO 2012. Meneghin et al : BNPVB family in Performance evaluation of inter-thread communication mechanisms on multicore/multithreaded architecture Dmitry Vyukov : bounded MPMC queue (highly recommended) Alex Otenko : US8607249 (highly related). John Mellor-Crummey : Concurrent queues: Practical fetch-and-phi algorithms. Technical Report 229, Department of Computer Science, University of Rochester Thomasson : FIFO Distributed Bakery Algorithm (very similar to PTLQueue). Scott and Scherer : Dual Data Structures I'll propose an optimization left as an exercise for the reader. Say we wanted to reduce memory usage by eliminating inter-slot padding. Such padding is usually "dark" memory and otherwise unused and wasted. But eliminating the padding leaves us at risk of increased false sharing. Furthermore lets say it was usually the case that the PutCursor and TakeCursor were numerically close to each other. (That's true in some use cases). We might still reduce false sharing by incrementing the cursors by some value other than 1 that is not trivially small and is coprime with the number of slots. Alternatively, we might increment the cursor by one and mask as usual, resulting in a logical index. We then use that logical index value to index into a permutation table, yielding an effective index for use in the slot array. The permutation table would be constructed so that nearby logical indices would map to more distant effective indices. (Open question: what should that permutation look like? Possibly some perversion of a Gray code or De Bruijn sequence might be suitable). As an aside, say we need to busy-wait for some condition as follows : "while C == 0 : Pause". Lets say that C is usually non-zero, so we typically don't wait. But when C happens to be 0 we'll have to spin for some period, possibly brief. We can arrange for the code to be more machine-friendly with respect to the branch predictors by transforming the loop into : "if C == 0 : for { Pause; if C != 0 : break; }". Critically, we want to restructure the loop so there's one branch that controls entry and another that controls loop exit. A concern is that your compiler or JIT might be clever enough to transform this back to "while C == 0 : Pause". You can sometimes avoid this by inserting a call to a some type of very cheap "opaque" method that the compiler can't elide or reorder. On Solaris, for instance, you could use :"if C == 0 : { gethrtime(); for { Pause; if C != 0 : break; }}". It's worth noting the obvious duality between locks and queues. If you have strict FIFO lock implementation with local spinning and succession by direct handoff such as MCS or CLH,then you can usually transform that lock into a queue. Hidden commentary and annotations - invisible : * And of course there's a well-known duality between queues and locks, but I'll leave that topic for another blog post. * Compare and contrast : PTLQ vs PTL and MultiLane * Equivalent : Turn; seq; sequence; pos; position; ticket * Put = Lock; Deposit Take = identify and reserve slot; wait; extract & clear; unlock * conceptualize : Distinct PutLock and TakeLock implemented as ticket lock or PTL Distinct arrival cursors but share per-slot "Turn" variable provides exclusive role-based access to slot's mailbox field put() acquires exclusive access to a slot for purposes of "deposit" assigns slot round-robin and then acquires deposit access rights/perms to that slot take() acquires exclusive access to slot for purposes of "withdrawal" assigns slot round-robin and then acquires withdrawal access rights/perms to that slot At any given time, only one thread can have withdrawal access to a slot at any given time, only one thread can have deposit access to a slot Permissible for T1 to have deposit access and T2 to simultaneously have withdrawal access * round-robin for the purposes of; role-based; access mode; access role mailslot; mailbox; allocate/assign/identify slot rights; permission; license; access permission; * PTL/Ticket hybrid Asymmetric usage ; owner oblivious lock-unlock pairing K-exclusion add Grant cursor pass message m from lock to unlock via Slots[] array Cursor performs 2 functions : + PTL ticket + Assigns request to slot in round-robin fashion Deconstruct protocol : explication put() : allocate slot in round-robin fashion acquire PTL for "put" access store message into slot associated with PTL index take() : Acquire PTL for "take" access // doorway step seq = fetchAdd (&Grant, 1) s = &Slots[seq & Mask] // waiting phase while s-Turn != seq : pause Extract : wait for s-mailbox to be full v = s-mailbox s-mailbox = null Release PTL for both "put" and "take" access s-Turn = seq + Mask + 1 * Slot round-robin assignment and lock "doorway" protocol leverage the same cursor and FetchAdd operation on that cursor FetchAdd (&Cursor,1) + round-robin slot assignment and dispersal + PTL/ticket lock "doorway" step waiting phase is via "Turn" field in slot * PTLQueue uses 2 cursors -- put and take. Acquire "put" access to slot via PTL-like lock Acquire "take" access to slot via PTL-like lock 2 locks : put and take -- at most one thread can access slot's mailbox Both locks use same "turn" field Like multilane : 2 cursors : put and take slot is simple 1-capacity mailbox instead of queue Borrow per-slot turn/grant from PTL Provides strict FIFO Lock slot : put-vs-put take-vs-take at most one put accesses slot at any one time at most one put accesses take at any one time reduction to 1-vs-1 instead of N-vs-M concurrency Per slot locks for put/take Release put/take by advancing turn * is instrumental in ... * P-V Semaphore vs lock vs K-exclusion * See also : FastQueues-excerpt.java dice-etc/queue-mpmc-bounded-blocking-circular-xadd/ * PTLQueue is the same as PTLQB - identical * Expedient return; ASAP; prompt; immediately * Lamport's Bakery algorithm : doorway step then waiting phase Threads arriving at doorway obtain a unique ticket number Threads enter in ticket order * In the terminology of Reed and Kanodia a ticket lock corresponds to the busy-wait implementation of a semaphore using an eventcount and a sequencer It can also be thought of as an optimization of Lamport's bakery lock was designed for fault-tolerance rather than performance Instead of spinning on the release counter, processors using a bakery lock repeatedly examine the tickets of their peers --

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  • New Tabs at End Opens New Tabs at the End of the Chrome Tab Bar

    - by Jason Fitzpatrick
    Chrome: If you’d prefer to have new tabs open at the end of the row instead of next to their parent tab, New Tabs at End is a simple Google Chrome extension that will scoot your tabs where you want them. It’s a minor thing, to be sure, but many users prefer to have tabs open at the end of the row–I know it took me quite awhile as a new Chrome user to get used to the default next-to-parent action. If you’d prefer to have the new tabs open at the end, hit up the link below to install New Tabs at End to tweak your tab bar workflow. New Tabs at End [via Addictive Tips] How To Be Your Own Personal Clone Army (With a Little Photoshop) How To Properly Scan a Photograph (And Get An Even Better Image) The HTG Guide to Hiding Your Data in a TrueCrypt Hidden Volume

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  • Microsoft Introduces WebMatrix

    - by Rick Strahl
    originally published in CoDe Magazine Editorial Microsoft recently released the first CTP of a new development environment called WebMatrix, which along with some of its supporting technologies are squarely aimed at making the Microsoft Web Platform more approachable for first-time developers and hobbyists. But in the process, it also provides some updated technologies that can make life easier for existing .NET developers. Let’s face it: ASP.NET development isn’t exactly trivial unless you already have a fair bit of familiarity with sophisticated development practices. Stick a non-developer in front of Visual Studio .NET or even the Visual Web Developer Express edition and it’s not likely that the person in front of the screen will be very productive or feel inspired. Yet other technologies like PHP and even classic ASP did provide the ability for non-developers and hobbyists to become reasonably proficient in creating basic web content quickly and efficiently. WebMatrix appears to be Microsoft’s attempt to bring back some of that simplicity with a number of technologies and tools. The key is to provide a friendly and fully self-contained development environment that provides all the tools needed to build an application in one place, as well as tools that allow publishing of content and databases easily to the web server. WebMatrix is made up of several components and technologies: IIS Developer Express IIS Developer Express is a new, self-contained development web server that is fully compatible with IIS 7.5 and based on the same codebase that IIS 7.5 uses. This new development server replaces the much less compatible Cassini web server that’s been used in Visual Studio and the Express editions. IIS Express addresses a few shortcomings of the Cassini server such as the inability to serve custom ISAPI extensions (i.e., things like PHP or ASP classic for example), as well as not supporting advanced authentication. IIS Developer Express provides most of the IIS 7.5 feature set providing much better compatibility between development and live deployment scenarios. SQL Server Compact 4.0 Database access is a key component for most web-driven applications, but on the Microsoft stack this has mostly meant you have to use SQL Server or SQL Server Express. SQL Server Compact is not new-it’s been around for a few years, but it’s been severely hobbled in the past by terrible tool support and the inability to support more than a single connection in Microsoft’s attempt to avoid losing SQL Server licensing. The new release of SQL Server Compact 4.0 supports multiple connections and you can run it in ASP.NET web applications simply by installing an assembly into the bin folder of the web application. In effect, you don’t have to install a special system configuration to run SQL Compact as it is a drop-in database engine: Copy the small assembly into your BIN folder (or from the GAC if installed fully), create a connection string against a local file-based database file, and then start firing SQL requests. Additionally WebMatrix includes nice tools to edit the database tables and files, along with tools to easily upsize (and hopefully downsize in the future) to full SQL Server. This is a big win, pending compatibility and performance limits. In my simple testing the data engine performed well enough for small data sets. This is not only useful for web applications, but also for desktop applications for which a fully installed SQL engine like SQL Server would be overkill. Having a local data store in those applications that can potentially be accessed by multiple users is a welcome feature. ASP.NET Razor View Engine What? Yet another native ASP.NET view engine? We already have Web Forms and various different flavors of using that view engine with Web Forms and MVC. Do we really need another? Microsoft thinks so, and Razor is an implementation of a lightweight, script-only view engine. Unlike the Web Forms view engine, Razor works only with inline code, snippets, and markup; therefore, it is more in line with current thinking of what a view engine should represent. There’s no support for a “page model” or any of the other Web Forms features of the full-page framework, but just a lightweight scripting engine that works with plain markup plus embedded expressions and code. The markup syntax for Razor is geared for minimal typing, plus some progressive detection of where a script block/expression starts and ends. This results in a much leaner syntax than the typical ASP.NET Web Forms alligator (<% %>) tags. Razor uses the @ sign plus standard C# (or Visual Basic) block syntax to delineate code snippets and expressions. Here’s a very simple example of what Razor markup looks like along with some comment annotations: <!DOCTYPE html> <html>     <head>         <title></title>     </head>     <body>     <h1>Razor Test</h1>          <!-- simple expressions -->     @DateTime.Now     <hr />     <!-- method expressions -->     @DateTime.Now.ToString("T")          <!-- code blocks -->     @{         List<string> names = new List<string>();         names.Add("Rick");         names.Add("Markus");         names.Add("Claudio");         names.Add("Kevin");     }          <!-- structured block statements -->     <ul>     @foreach(string name in names){             <li>@name</li>     }     </ul>           <!-- Conditional code -->        @if(true) {                        <!-- Literal Text embedding in code -->        <text>         true        </text>;    }    else    {        <!-- Literal Text embedding in code -->       <text>       false       </text>;    }    </body> </html> Like the Web Forms view engine, Razor parses pages into code, and then executes that run-time compiled code. Effectively a “page” becomes a code file with markup becoming literal text written into the Response stream, code snippets becoming raw code, and expressions being written out with Response.Write(). The code generated from Razor doesn’t look much different from similar Web Forms code that only uses script tags; so although the syntax may look different, the operational model is fairly similar to the Web Forms engine minus the overhead of the large Page object model. However, there are differences: -Razor pages are based on a new base class, Microsoft.WebPages.WebPage, which is hosted in the Microsoft.WebPages assembly that houses all the Razor engine parsing and processing logic. Browsing through the assembly (in the generated ASP.NET Temporary Files folder or GAC) will give you a good idea of the functionality that Razor provides. If you look closely, a lot of the feature set matches ASP.NET MVC’s view implementation as well as many of the helper classes found in MVC. It’s not hard to guess the motivation for this sort of view engine: For beginning developers the simple markup syntax is easier to work with, although you obviously still need to have some understanding of the .NET Framework in order to create dynamic content. The syntax is easier to read and grok and much shorter to type than ASP.NET alligator tags (<% %>) and also easier to understand aesthetically what’s happening in the markup code. Razor also is a better fit for Microsoft’s vision of ASP.NET MVC: It’s a new view engine without the baggage of Web Forms attached to it. The engine is more lightweight since it doesn’t carry all the features and object model of Web Forms with it and it can be instantiated directly outside of the HTTP environment, which has been rather tricky to do for the Web Forms view engine. Having a standalone script parser is a huge win for other applications as well – it makes it much easier to create script or meta driven output generators for many types of applications from code/screen generators, to simple form letters to data merging applications with user customizability. For me personally this is very useful side effect and who knows maybe Microsoft will actually standardize they’re scripting engines (die T4 die!) on this engine. Razor also better fits the “view-based” approach where the view is supposed to be mostly a visual representation that doesn’t hold much, if any, code. While you can still use code, the code you do write has to be self-contained. Overall I wouldn’t be surprised if Razor will become the new standard view engine for MVC in the future – and in fact there have been announcements recently that Razor will become the default script engine in ASP.NET MVC 3.0. Razor can also be used in existing Web Forms and MVC applications, although that’s not working currently unless you manually configure the script mappings and add the appropriate assemblies. It’s possible to do it, but it’s probably better to wait until Microsoft releases official support for Razor scripts in Visual Studio. Once that happens, you can simply drop .cshtml and .vbhtml pages into an existing ASP.NET project and they will work side by side with classic ASP.NET pages. WebMatrix Development Environment To tie all of these three technologies together, Microsoft is shipping WebMatrix with an integrated development environment. An integrated gallery manager makes it easy to download and load existing projects, and then extend them with custom functionality. It seems to be a prominent goal to provide community-oriented content that can act as a starting point, be it via a custom templates or a complete standard application. The IDE includes a project manager that works with a single project and provides an integrated IDE/editor for editing the .cshtml and .vbhtml pages. A run button allows you to quickly run pages in the project manager in a variety of browsers. There’s no debugging support for code at this time. Note that Razor pages don’t require explicit compilation, so making a change, saving, and then refreshing your page in the browser is all that’s needed to see changes while testing an application locally. It’s essentially using the auto-compiling Web Project that was introduced with .NET 2.0. All code is compiled during run time into dynamically created assemblies in the ASP.NET temp folder. WebMatrix also has PHP Editing support with syntax highlighting. You can load various PHP-based applications from the WebMatrix Web Gallery directly into the IDE. Most of the Web Gallery applications are ready to install and run without further configuration, with Wizards taking you through installation of tools, dependencies, and configuration of the database as needed. WebMatrix leverages the Web Platform installer to pull the pieces down from websites in a tight integration of tools that worked nicely for the four or five applications I tried this out on. Click a couple of check boxes and fill in a few simple configuration options and you end up with a running application that’s ready to be customized. Nice! You can easily deploy completed applications via WebDeploy (to an IIS server) or FTP directly from within the development environment. The deploy tool also can handle automatically uploading and installing the database and all related assemblies required, making deployment a simple one-click install step. Simplified Database Access The IDE contains a database editor that can edit SQL Compact and SQL Server databases. There is also a Database helper class that facilitates database access by providing easy-to-use, high-level query execution and iteration methods: @{       var db = Database.OpenFile("FirstApp.sdf");     string sql = "select * from customers where Id > @0"; } <ul> @foreach(var row in db.Query(sql,1)){         <li>@row.FirstName @row.LastName</li> } </ul> The query function takes a SQL statement plus any number of positional (@0,@1 etc.) SQL parameters by simple values. The result is returned as a collection of rows which in turn have a row object with dynamic properties for each of the columns giving easy (though untyped) access to each of the fields. Likewise Execute and ExecuteNonQuery allow execution of more complex queries using similar parameter passing schemes. Note these queries use string-based queries rather than LINQ or Entity Framework’s strongly typed LINQ queries. While this may seem like a step back, it’s also in line with the expectations of non .NET script developers who are quite used to writing and using SQL strings in code rather than using OR/M frameworks. The only question is why was something not included from the beginning in .NET and Microsoft made developers build custom implementations of these basic building blocks. The implementation looks a lot like a DataTable-style data access mechanism, but to be fair, this is a common approach in scripting languages. This type of syntax that uses simple, static, data object methods to perform simple data tasks with one line of code are common in scripting languages and are a good match for folks working in PHP/Python, etc. Seems like Microsoft has taken great advantage of .NET 4.0’s dynamic typing to provide this sort of interface for row iteration where each row has properties for each field. FWIW, all the examples demonstrate using local SQL Compact files - I was unable to get a SQL Server connection string to work with the Database class (the connection string wasn’t accepted). However, since the code in the page is still plain old .NET, you can easily use standard ADO.NET code or even LINQ or Entity Framework models that are created outside of WebMatrix in separate assemblies as required. The good the bad the obnoxious - It’s still .NET The beauty (or curse depending on how you look at it :)) of Razor and the compilation model is that, behind it all, it’s still .NET. Although the syntax may look foreign, it’s still all .NET behind the scenes. You can easily access existing tools, helpers, and utilities simply by adding them to the project as references or to the bin folder. Razor automatically recognizes any assembly reference from assemblies in the bin folder. In the default configuration, Microsoft provides a host of helper functions in a Microsoft.WebPages assembly (check it out in the ASP.NET temp folder for your application), which includes a host of HTML Helpers. If you’ve used ASP.NET MVC before, a lot of the helpers should look familiar. Documentation at the moment is sketchy-there’s a very rough API reference you can check out here: http://www.asp.net/webmatrix/tutorials/asp-net-web-pages-api-reference Who needs WebMatrix? Uhm… good Question Clearly Microsoft is trying hard to create an environment with WebMatrix that is easy to use for newbie developers. The goal seems to be simplicity in providing a minimal development environment and an easy-to-use script engine/language that makes it easy to get started with. There’s also some focus on community features that can be used as starting points, such as Web Gallery applications and templates. The community features in particular are very nice and something that would be nice to eventually see in Visual Studio as well. The question is whether this is too little too late. Developers who have been clamoring for a simpler development environment on the .NET stack have mostly left for other simpler platforms like PHP or Python which are catering to the down and dirty developer. Microsoft will be hard pressed to win those folks-and other hardcore PHP developers-back. Regardless of how much you dress up a script engine fronted by the .NET Framework, it’s still the .NET Framework and all the complexity that drives it. While .NET is a fine solution in its breadth and features once you get a basic handle on the core features, the bar of entry to being productive with the .NET Framework is still pretty high. The MVC style helpers Microsoft provides are a good step in the right direction, but I suspect it’s not enough to shield new developers from having to delve much deeper into the Framework to get even basic applications built. Razor and its helpers is trying to make .NET more accessible but the reality is that in order to do useful stuff that goes beyond the handful of simple helpers you still are going to have to write some C# or VB or other .NET code. If the target is a hobby/amateur/non-programmer the learning curve isn’t made any easier by WebMatrix it’s just been shifted a tad bit further along in your development endeavor when you run out of canned components that are supplied either by Microsoft or the community. The database helpers are interesting and actually I’ve heard a lot of discussion from various developers who’ve been resisting .NET for a really long time perking up at the prospect of easier data access in .NET than the ridiculous amount of code it takes to do even simple data access with raw ADO.NET. It seems sad that such a simple concept and implementation should trigger this sort of response (especially since it’s practically trivial to create helpers like these or pick them up from countless libraries available), but there it is. It also shows that there are plenty of developers out there who are more interested in ‘getting stuff done’ easily than necessarily following the latest and greatest practices which are overkill for many development scenarios. Sometimes it seems that all of .NET is focused on the big life changing issues of development, rather than the bread and butter scenarios that many developers are interested in to get their work accomplished. And that in the end may be WebMatrix’s main raison d'être: To bring some focus back at Microsoft that simpler and more high level solutions are actually needed to appeal to the non-high end developers as well as providing the necessary tools for the high end developers who want to follow the latest and greatest trends. The current version of WebMatrix hits many sweet spots, but it also feels like it has a long way to go before it really can be a tool that a beginning developer or an accomplished developer can feel comfortable with. Although there are some really good ideas in the environment (like the gallery for downloading apps and components) which would be a great addition for Visual Studio as well, the rest of the development environment just feels like crippleware with required functionality missing especially debugging and Intellisense, but also general editor support. It’s not clear whether these are because the product is still in an early alpha release or whether it’s simply designed that way to be a really limited development environment. While simple can be good, nobody wants to feel left out when it comes to necessary tool support and WebMatrix just has that left out feeling to it. If anything WebMatrix’s technology pieces (which are really independent of the WebMatrix product) are what are interesting to developers in general. The compact IIS implementation is a nice improvement for development scenarios and SQL Compact 4.0 seems to address a lot of concerns that people have had and have complained about for some time with previous SQL Compact implementations. By far the most interesting and useful technology though seems to be the Razor view engine for its light weight implementation and it’s decoupling from the ASP.NET/HTTP pipeline to provide a standalone scripting/view engine that is pluggable. The first winner of this is going to be ASP.NET MVC which can now have a cleaner view model that isn’t inconsistent due to the baggage of non-implemented WebForms features that don’t work in MVC. But I expect that Razor will end up in many other applications as a scripting and code generation engine eventually. Visual Studio integration for Razor is currently missing, but is promised for a later release. The ASP.NET MVC team has already mentioned that Razor will eventually become the default MVC view engine, which will guarantee continued growth and development of this tool along those lines. And the Razor engine and support tools actually inherit many of the features that MVC pioneered, so there’s some synergy flowing both ways between Razor and MVC. As an existing ASP.NET developer who’s already familiar with Visual Studio and ASP.NET development, the WebMatrix IDE doesn’t give you anything that you want. The tools provided are minimal and provide nothing that you can’t get in Visual Studio today, except the minimal Razor syntax highlighting, so there’s little need to take a step back. With Visual Studio integration coming later there’s little reason to look at WebMatrix for tooling. It’s good to see that Microsoft is giving some thought about the ease of use of .NET as a platform For so many years, we’ve been piling on more and more new features without trying to take a step back and see how complicated the development/configuration/deployment process has become. Sometimes it’s good to take a step - or several steps - back and take another look and realize just how far we’ve come. WebMatrix is one of those reminders and one that likely will result in some positive changes on the platform as a whole. © Rick Strahl, West Wind Technologies, 2005-2010Posted in ASP.NET   IIS7  

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  • Space partitioning when everything is moving

    - by Roy T.
    Background Together with a friend I'm working on a 2D game that is set in space. To make it as immersive and interactive as possible we want there to be thousands of objects freely floating around, some clustered together, others adrift in empty space. Challenge To unburden the rendering and physics engine we need to implement some sort of spatial partitioning. There are two challenges we have to overcome. The first challenge is that everything is moving so reconstructing/updating the data structure has to be extremely cheap since it will have to be done every frame. The second challenge is the distribution of objects, as said before there might be clusters of objects together and vast bits of empty space and to make it even worse there is no boundary to space. Existing technologies I've looked at existing techniques like BSP-Trees, QuadTrees, kd-Trees and even R-Trees but as far as I can tell these data structures aren't a perfect fit since updating a lot of objects that have moved to other cells is relatively expensive. What I've tried I made the decision that I need a data structure that is more geared toward rapid insertion/update than on giving back the least amount of possible hits given a query. For that purpose I made the cells implicit so each object, given it's position, can calculate in which cell(s) it should be. Then I use a HashMap that maps cell-coordinates to an ArrayList (the contents of the cell). This works fairly well since there is no memory lost on 'empty' cells and its easy to calculate which cells to inspect. However creating all those ArrayLists (worst case N) is expensive and so is growing the HashMap a lot of times (although that is slightly mitigated by giving it a large initial capacity). Problem OK so this works but still isn't very fast. Now I can try to micro-optimize the JAVA code. However I'm not expecting too much of that since the profiler tells me that most time is spent in creating all those objects that I use to store the cells. I'm hoping that there are some other tricks/algorithms out there that make this a lot faster so here is what my ideal data structure looks like: The number one priority is fast updating/reconstructing of the entire data structure Its less important to finely divide the objects into equally sized bins, we can draw a few extra objects and do a few extra collision checks if that means that updating is a little bit faster Memory is not really important (PC game)

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  • Store a formula in a table and use the formula in a javascript/PHP function

    - by Muhaimin Abdul
    I have a MySql database where part of it handles instrument's depth of water. Each instrument has its own formula of calculation how depth the water when the operator collect the reading I stored the formula for each instrument in database/MySql. Example formula: [55-57] this is the simple minus operation, where the number is actually represent the id of a row. How do I represent those number with id of a row and later convert it to javascript readable code. I simply want to do keyup event where everytime user key in something into text field then the other part of HTML would reflect changes based on formula that I fetched from database FYI, I'm using BackboneJS together with RequireJS

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  • Running Multiple Queries in Oracle SQL Developer

    - by thatjeffsmith
    There are two methods for running queries in SQL Developer: Run Statement Run Statement, Shift+Enter, F9, or this button Run Script No grids, just script (SQL*Plus like) ouput is fine, thank you very much! What’s the Difference? There are some obvious differences between the two features, the most obvious being the format of the output delivered. But there are some other, more subtle differences here, primarily around fetching. What is Fetch? After you run send your query to Oracle, it has to do 3 things: Parse Execute Fetch Technically it has to do at least 2 things, and sometimes only 1. But, to get the data back to the user, the fetch must occur. If you have a 10 row query or a 1,000,000 row query, this can mean 1 or many fetches in groups of records. Ok, before I went on the Fetch tangent, I said there were two ways to run statements in SQL Developer: Run Statement Run statement brings your query results to a grid with a single fetch. The user sees 50, 100, 500, etc rows come back, but SQL Developer and the database know that there are more rows waiting to be retrieved. The process on the server that was used to execute the query is still hanging around too. To alleviate this, increase your fetch size to 500. Every query ran will come back with the first 500 rows, and rows will be continued to be fetched in 500 row increments. You’ll then see most of your ad hoc queries complete with a single fetch. Scroll down, or hit Ctrl+End to force a full fetch and get all your rows back. Run Script Run Script runs the contents of the worksheet (or what’s highlighted) as a ‘script.’ What does that mean exactly? Think of this as being equivalent to running this in SQL*Plus: @my_script.sql; Each statement is executed. Also, ALL rows are fetched. So once it’s finished executing, there are no open cursors left around. The more obvious difference here is that the output comes back formatted as plain old text. Run one or more commands plus SQL*Plus commands like SET and SPOOL The Trick: Run Statement Works With Multiple Statements! It says ‘run statement,’ but if you select more than one with your mouse and hit the button – it will run each and throw the results to 1 grid for each statement. If you mouse hover over the Query Result panel tab, SQL Developer will tell you the query used to populate that grid. This will work regardless of what you have this preference set to: DATABASE – WORKSHEET – SHOW QUERY RESULTS IN NEW TABS Mind the fetch though! Close those cursors by bring back all the records or closing the grids when you’re done with them.

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  • Design review for application facing memory issues

    - by Mr Moose
    I apologise in advance for the length of this post, but I want to paint an accurate picture of the problems my app is facing and then pose some questions below; I am trying to address some self inflicted design pain that is now leading to my application crashing due to out of memory errors. An abridged description of the problem domain is as follows; The application takes in a “dataset” that consists of numerous text files containing related data An individual text file within the dataset usually contains approx 20 “headers” that contain metadata about the data it contains. It also contains a large tab delimited section containing data that is related to data in one of the other text files contained within the dataset. The number of columns per file is very variable from 2 to 256+ columns. The original application was written to allow users to load a dataset, map certain columns of each of the files which basically indicating key information on the files to show how they are related as well as identify a few expected column names. Once this is done, a validation process takes place to enforce various rules and ensure that all the relationships between the files are valid. Once that is done, the data is imported into a SQL Server database. The database design is an EAV (Entity-Attribute-Value) model used to cater for the variable columns per file. I know EAV has its detractors, but in this case, I feel it was a reasonable choice given the disparate data and variable number of columns submitted in each dataset. The memory problem Given the fact the combined size of all text files was at most about 5 megs, and in an effort to reduce the database transaction time, it was decided to read ALL the data from files into memory and then perform the following; perform all the validation whilst the data was in memory relate it using an object model Start DB transaction and write the key columns row by row, noting the Id of the written row (all tables in the database utilise identity columns), then the Id of the newly written row is applied to all related data Once all related data had been updated with the key information to which it relates, these records are written using SqlBulkCopy. Due to our EAV model, we essentially have; x columns by y rows to write, where x can by 256+ and rows are often into the tens of thousands. Once all the data is written without error (can take several minutes for large datasets), Commit the transaction. The problem now comes from the fact we are now receiving individual files containing over 30 megs of data. In a dataset, we can receive any number of files. We’ve started seen datasets of around 100 megs coming in and I expect it is only going to get bigger from here on in. With files of this size, data can’t even be read into memory without the app falling over, let alone be validated and imported. I anticipate having to modify large chunks of the code to allow validation to occur by parsing files line by line and am not exactly decided on how to handle the import and transactions. Potential improvements I’ve wondered about using GUIDs to relate the data rather than relying on identity fields. This would allow data to be related prior to writing to the database. This would certainly increase the storage required though. Especially in an EAV design. Would you think this is a reasonable thing to try, or do I simply persist with identity fields (natural keys can’t be trusted to be unique across all submitters). Use of staging tables to get data into the database and only performing the transaction to copy data from staging area to actual destination tables. Questions For systems like this that import large quantities of data, how to you go about keeping transactions small. I’ve kept them as small as possible in the current design, but they are still active for several minutes and write hundreds of thousands of records in one transaction. Is there a better solution? The tab delimited data section is read into a DataTable to be viewed in a grid. I don’t need the full functionality of a DataTable, so I suspect it is overkill. Is there anyway to turn off various features of DataTables to make them more lightweight? Are there any other obvious things you would do in this situation to minimise the memory footprint of the application described above? Thanks for your kind attention.

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  • xsltproc killed, out of memory

    - by David Parks
    I'm trying to split up a 13GB xml file into small ~50MB xml files with this XSLT style sheet. But this process kills xsltproc after I see it taking up over 1.7GB of memory (that's the total on the system). Is there any way to deal with huge XML files with xsltproc? Can I change my style sheet? Or should I use a different processor? Or am I just S.O.L.? <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0" xmlns:exsl="http://exslt.org/common" extension-element-prefixes="exsl" xmlns:fn="http://www.w3.org/2005/xpath-functions"> <xsl:output method="xml" indent="yes"/> <xsl:strip-space elements="*"/> <xsl:param name="block-size" select="75000"/> <xsl:template match="/"> <xsl:copy> <xsl:apply-templates select="mysqldump/database/table_data/row[position() mod $block-size = 1]" /> </xsl:copy> </xsl:template> <xsl:template match="row"> <exsl:document href="chunk-{position()}.xml"> <add> <xsl:for-each select=". | following-sibling::row[position() &lt; $block-size]" > <doc> <xsl:for-each select="field"> <field> <xsl:attribute name="name"><xsl:value-of select="./@name"/></xsl:attribute> <xsl:value-of select="."/> </field> <xsl:text>&#xa;</xsl:text> </xsl:for-each> </doc> </xsl:for-each> </add> </exsl:document> </xsl:template>

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  • 8-Puzzle Solution executes infinitely [migrated]

    - by Ashwin
    I am looking for a solution to 8-puzzle problem using the A* Algorithm. I found this project on the internet. Please see the files - proj1 and EightPuzzle. The proj1 contains the entry point for the program(the main() function) and EightPuzzle describes a particular state of the puzzle. Each state is an object of the 8-puzzle. I feel that there is nothing wrong in the logic. But it loops forever for these two inputs that I have tried : {8,2,7,5,1,6,3,0,4} and {3,1,6,8,4,5,7,2,0}. Both of them are valid input states. What is wrong with the code? Note For better viewing copy the code in a Notepad++ or some other text editor(which has the capability to recognize java source file) because there are lot of comments in the code. Since A* requires a heuristic, they have provided the option of using manhattan distance and a heuristic that calculates the number of misplaced tiles. And to ensure that the best heuristic is executed first, they have implemented a PriorityQueue. The compareTo() function is implemented in the EightPuzzle class. The input to the program can be changed by changing the value of p1d in the main() function of proj1 class. The reason I am telling that there exists solution for the two my above inputs is because the applet here solves them. Please ensure that you select 8-puzzle from teh options in the applet. EDITI gave this input {0,5,7,6,8,1,2,4,3}. It took about 10 seconds and gave a result with 26 moves. But the applet gave a result with 24 moves in 0.0001 seconds with A*. For quick reference I have pasted the the two classes without the comments : EightPuzzle import java.util.*; public class EightPuzzle implements Comparable <Object> { int[] puzzle = new int[9]; int h_n= 0; int hueristic_type = 0; int g_n = 0; int f_n = 0; EightPuzzle parent = null; public EightPuzzle(int[] p, int h_type, int cost) { this.puzzle = p; this.hueristic_type = h_type; this.h_n = (h_type == 1) ? h1(p) : h2(p); this.g_n = cost; this.f_n = h_n + g_n; } public int getF_n() { return f_n; } public void setParent(EightPuzzle input) { this.parent = input; } public EightPuzzle getParent() { return this.parent; } public int inversions() { /* * Definition: For any other configuration besides the goal, * whenever a tile with a greater number on it precedes a * tile with a smaller number, the two tiles are said to be inverted */ int inversion = 0; for(int i = 0; i < this.puzzle.length; i++ ) { for(int j = 0; j < i; j++) { if(this.puzzle[i] != 0 && this.puzzle[j] != 0) { if(this.puzzle[i] < this.puzzle[j]) inversion++; } } } return inversion; } public int h1(int[] list) // h1 = the number of misplaced tiles { int gn = 0; for(int i = 0; i < list.length; i++) { if(list[i] != i && list[i] != 0) gn++; } return gn; } public LinkedList<EightPuzzle> getChildren() { LinkedList<EightPuzzle> children = new LinkedList<EightPuzzle>(); int loc = 0; int temparray[] = new int[this.puzzle.length]; EightPuzzle rightP, upP, downP, leftP; while(this.puzzle[loc] != 0) { loc++; } if(loc % 3 == 0){ temparray = this.puzzle.clone(); temparray[loc] = temparray[loc + 1]; temparray[loc + 1] = 0; rightP = new EightPuzzle(temparray, this.hueristic_type, this.g_n + 1); rightP.setParent(this); children.add(rightP); }else if(loc % 3 == 1){ //add one child swaps with right temparray = this.puzzle.clone(); temparray[loc] = temparray[loc + 1]; temparray[loc + 1] = 0; rightP = new EightPuzzle(temparray, this.hueristic_type, this.g_n + 1); rightP.setParent(this); children.add(rightP); //add one child swaps with left temparray = this.puzzle.clone(); temparray[loc] = temparray[loc - 1]; temparray[loc - 1] = 0; leftP = new EightPuzzle(temparray, this.hueristic_type, this.g_n + 1); leftP.setParent(this); children.add(leftP); }else if(loc % 3 == 2){ // add one child swaps with left temparray = this.puzzle.clone(); temparray[loc] = temparray[loc - 1]; temparray[loc - 1] = 0; leftP = new EightPuzzle(temparray, this.hueristic_type, this.g_n + 1); leftP.setParent(this); children.add(leftP); } if(loc / 3 == 0){ //add one child swaps with lower temparray = this.puzzle.clone(); temparray[loc] = temparray[loc + 3]; temparray[loc + 3] = 0; downP = new EightPuzzle(temparray, this.hueristic_type, this.g_n + 1); downP.setParent(this); children.add(downP); }else if(loc / 3 == 1 ){ //add one child, swap with upper temparray = this.puzzle.clone(); temparray[loc] = temparray[loc - 3]; temparray[loc - 3] = 0; upP = new EightPuzzle(temparray, this.hueristic_type, this.g_n + 1); upP.setParent(this); children.add(upP); //add one child, swap with lower temparray = this.puzzle.clone(); temparray[loc] = temparray[loc + 3]; temparray[loc + 3] = 0; downP = new EightPuzzle(temparray, this.hueristic_type, this.g_n + 1); downP.setParent(this); children.add(downP); }else if (loc / 3 == 2 ){ //add one child, swap with upper temparray = this.puzzle.clone(); temparray[loc] = temparray[loc - 3]; temparray[loc - 3] = 0; upP = new EightPuzzle(temparray, this.hueristic_type, this.g_n + 1); upP.setParent(this); children.add(upP); } return children; } public int h2(int[] list) // h2 = the sum of the distances of the tiles from their goal positions // for each item find its goal position // calculate how many positions it needs to move to get into that position { int gn = 0; int row = 0; int col = 0; for(int i = 0; i < list.length; i++) { if(list[i] != 0) { row = list[i] / 3; col = list[i] % 3; row = Math.abs(row - (i / 3)); col = Math.abs(col - (i % 3)); gn += row; gn += col; } } return gn; } public String toString() { String x = ""; for(int i = 0; i < this.puzzle.length; i++){ x += puzzle[i] + " "; if((i + 1) % 3 == 0) x += "\n"; } return x; } public int compareTo(Object input) { if (this.f_n < ((EightPuzzle) input).getF_n()) return -1; else if (this.f_n > ((EightPuzzle) input).getF_n()) return 1; return 0; } public boolean equals(EightPuzzle test){ if(this.f_n != test.getF_n()) return false; for(int i = 0 ; i < this.puzzle.length; i++) { if(this.puzzle[i] != test.puzzle[i]) return false; } return true; } public boolean mapEquals(EightPuzzle test){ for(int i = 0 ; i < this.puzzle.length; i++) { if(this.puzzle[i] != test.puzzle[i]) return false; } return true; } } proj1 import java.util.*; public class proj1 { /** * @param args */ public static void main(String[] args) { int[] p1d = {1, 4, 2, 3, 0, 5, 6, 7, 8}; int hueristic = 2; EightPuzzle start = new EightPuzzle(p1d, hueristic, 0); int[] win = { 0, 1, 2, 3, 4, 5, 6, 7, 8}; EightPuzzle goal = new EightPuzzle(win, hueristic, 0); astar(start, goal); } public static void astar(EightPuzzle start, EightPuzzle goal) { if(start.inversions() % 2 == 1) { System.out.println("Unsolvable"); return; } // function A*(start,goal) // closedset := the empty set // The set of nodes already evaluated. LinkedList<EightPuzzle> closedset = new LinkedList<EightPuzzle>(); // openset := set containing the initial node // The set of tentative nodes to be evaluated. priority queue PriorityQueue<EightPuzzle> openset = new PriorityQueue<EightPuzzle>(); openset.add(start); while(openset.size() > 0){ // x := the node in openset having the lowest f_score[] value EightPuzzle x = openset.peek(); // if x = goal if(x.mapEquals(goal)) { // return reconstruct_path(came_from, came_from[goal]) Stack<EightPuzzle> toDisplay = reconstruct(x); System.out.println("Printing solution... "); System.out.println(start.toString()); print(toDisplay); return; } // remove x from openset // add x to closedset closedset.add(openset.poll()); LinkedList <EightPuzzle> neighbor = x.getChildren(); // foreach y in neighbor_nodes(x) while(neighbor.size() > 0) { EightPuzzle y = neighbor.removeFirst(); // if y in closedset if(closedset.contains(y)){ // continue continue; } // tentative_g_score := g_score[x] + dist_between(x,y) // // if y not in openset if(!closedset.contains(y)){ // add y to openset openset.add(y); // } // } // } } public static void print(Stack<EightPuzzle> x) { while(!x.isEmpty()) { EightPuzzle temp = x.pop(); System.out.println(temp.toString()); } } public static Stack<EightPuzzle> reconstruct(EightPuzzle winner) { Stack<EightPuzzle> correctOutput = new Stack<EightPuzzle>(); while(winner.getParent() != null) { correctOutput.add(winner); winner = winner.getParent(); } return correctOutput; } }

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  • lock screen before hibernating [12.04]

    - by Emanuel Ey
    So when i hibernate my laptop the screen doesn't lock automatically. To solve this if changed /etc/acpi/powerbtn.sh to contain: su - myUsername -c "gnome-screensaver-command -l" sudo pm-hibernate exit 0 When running this file from a command line it works as intended (ie, lock the screen and then hibernate). Unfortunately, when pressing the power button, it still just hibernates without locking the screen -what am I missing? EDIT: I've added the line whoami>>~/Desktop/test.txt to verify which user is executing the /etc/acpi/powerbtn.shscript. When pressing the power button, the file test.txt is created, but is empty. From this i conclude that the script is in fact being called when pressing the power button. What i do not understand is how the output of whoami can be empty...

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  • deciphering columnar transposition cipher

    - by Arfan M
    I am looking for an idea on how to decipher a columnar transposition cipher without knowing the key or the length of the key. When I take the cipher text as input to my algorithm I will guess the length of the key to be the factors of the length of the cipher text. I will take the first factor suppose the length was 20 letters so I will take 2*10 (2 rows and 10 columns). Now I want to arrange the cipher text in the columns and read it row wise to see if there is any word forming and match it with a dictionary if it is something sensible. If it matches the dictionary then it means it is in correct order or else I want to know how to make other combinations of the columns and read the string again row wise. Please suggest another approach that is more efficient.

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  • Slick2D: Animation not being parsed from spritesheet correctly

    - by user2066880
    I have a 960x960 spritesheet with each tile being 192x192. I initialized my spritesheet and animation like so: spritesheet = new SpriteSheet("resources/spritesheets/player.png", 192, 192); walkingLeft = new Animation(spritesheet, 3, 0, 0, 1, true, 20, true); When I attempt to render the animation, I get a java.lang.ArrayIndexOutOfBoundsException: -1 error. This error doesn't occur when I'm creating an animation from images in the same row. Therefore, I'm assuming that the error is being caused because of the way Slick is handling horizontal scanning (going to the next row after reaching the end).

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  • A WPF Image/Text Button

    - by psheriff
    Some of our customers are asking us to give them a Windows 8 look and feel for their applications. This includes things like buttons, tiles, application bars, and other features. In this blog post I will describe how to create a button that looks similar to those you will find in a Windows 8 application bar. In Figure 1 you can see two different kinds of buttons. In the top row is a WPF button where the content of the button includes a Border, an Image and a TextBlock. In the bottom row are four...(read more)

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  • Basic Form Properties and Modality in VB.NET

    Creating your First VB.NET Form 1. Launch Microsoft Visual Basic 2008 Express Edition. If you do not have this program, then you cannot create VB.NET forms. You can read an introductory tutorial on how to install Visual Basic on your computer: http://www.aspfree.com/c/a/VB.NET/Visual-Basic-for-Beginners/ 2. Go to File - gt; New Project. 3. Since you will be creating a form, select Windows Forms Application. 4. Select a name for your form project, e.g. MyFirstForm. 5. Hit OK to get started. 6. You will then see an empty form -- just like an empty canvas when you paint. It looks like th...

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  • To Bit or Not To Bit

    - by Johnm
    'Twas a long day of troubleshooting and firefighting and now, with most of the office vacant, you face a blank scripting window to create a new table in his database. Many questions circle your mind like dirty water gurgling down the bathtub drain: "How normalized should this table be?", "Should I use an identity column?", "NVarchar or Varchar?", "Should this column be NULLABLE?", "I wonder what apple blue cheese bacon cheesecake tastes like?" Well, there are times when the mind goes it's own direction. A Bit About Bit At some point during your table creation efforts you will encounter the decision of whether to use the bit data type for a column. The bit data type is an integer data type that recognizes only the values of 1, 0 and NULL as valid. This data type is often utilized to store yes/no or true/false values. An example of its use would be a column called [IsGasoline] which would be intended to contain the value of 1 if the row's subject (a car) had a gasoline engine and a 0 if the subject did not have a gasoline engine. The bit data type can even be found in some of the system tables of SQL Server. For example, the sysssispackages table in the msdb database which contains SQL Server Integration Services Package information for the packages stored in SQL Server. This table contains a column called [IsEncrypted]. A value of 1 indicates that the package has been encrypted while the value of 0 indicates that it is not. I have learned that the most effective way to disperse the crowd that surrounds the office coffee machine is to engage into SQL Server debates. The bit data type has been one of the most reoccurring, as well as the most enjoyable, of these topics. It contains a practical side and a philosophical side. Practical Consideration This data type certainly has its place and is a valuable option for database design; but it is often used in situations where the answer is really not a pure true/false response. In addition, true/false values are not very informative or scalable. Let's use the previously noted [IsGasoline] column for illustration. While on the surface it appears to be a rather simple question when evaluating a car: "Does the car have a gasoline engine?" If the person entering data is entering a row for a Jeep Liberty, the response would be a 1 since it has a gasoline engine. If the person is entering data is entering a row for a Chevrolet Volt, the response would be a 0 since it is an electric engine. What happens when a person is entering a row for the gasoline/electric hybrid Toyota Prius? Would one person's conclusion be consistent with another person's conclusion? The argument could be made that the current intent for the database is to be used only for pure gasoline and pure electric engines; but this is where the scalability issue comes into play. With the use of a bit data type a database modification and data conversion would be required if the business decided to take on hybrid engines. Whereas, alternatively, if the int data type were used as a foreign key to a reference table containing the engine type options, the change to include the hybrid option would only require an entry into the reference table. Philosophical Consideration Since the bit data type is often used for true/false or yes/no data (also called Boolean) it presents a philosophical conundrum of what to do about the allowance of the NULL value. The inclusion of NULL in a true/false or yes/no response simply violates the logical principle of bivalence which states that "every proposition is either true or false". If NULL is not true, then it must be false. The mathematical laws of Boolean logic support this concept by stating that the only valid values of this scenario are 1 and 0. There is another way to look at this conundrum: NULL is also considered to be the absence of a response. In other words, it is the equivalent to "undecided". Anyone who watches the news can tell you that polls always include an "undecided" option. This could be considered a valid option in the world of yes/no/dunno. Through out all of these considerations I have discovered one absolute certainty: When you have found a person, or group of persons, who are willing to entertain a philosophical debate of the bit data type, you have found some true friends.

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  • Anatomy of a .NET Assembly - CLR metadata 2

    - by Simon Cooper
    Before we look any further at the CLR metadata, we need a quick diversion to understand how the metadata is actually stored. Encoding table information As an example, we'll have a look at a row in the TypeDef table. According to the spec, each TypeDef consists of the following: Flags specifying various properties of the class, including visibility. The name of the type. The namespace of the type. What type this type extends. The field list of this type. The method list of this type. How is all this data actually represented? Offset & RID encoding Most assemblies don't need to use a 4 byte value to specify heap offsets and RIDs everywhere, however we can't hard-code every offset and RID to be 2 bytes long as there could conceivably be more than 65535 items in a heap or more than 65535 fields or types defined in an assembly. So heap offsets and RIDs are only represented in the full 4 bytes if it is required; in the header information at the top of the #~ stream are 3 bits indicating if the #Strings, #GUID, or #Blob heaps use 2 or 4 bytes (the #US stream is not accessed from metadata), and the rowcount of each table. If the rowcount for a particular table is greater than 65535 then all RIDs referencing that table throughout the metadata use 4 bytes, else only 2 bytes are used. Coded tokens Not every field in a table row references a single predefined table. For example, in the TypeDef extends field, a type can extend another TypeDef (a type in the same assembly), a TypeRef (a type in a different assembly), or a TypeSpec (an instantiation of a generic type). A token would have to be used to let us specify the table along with the RID. Tokens are always 4 bytes long; again, this is rather wasteful of space. Cutting the RID down to 2 bytes would make each token 3 bytes long, which isn't really an optimum size for computers to read from memory or disk. However, every use of a token in the metadata tables can only point to a limited subset of the metadata tables. For the extends field, we only need to be able to specify one of 3 tables, which we can do using 2 bits: 0x0: TypeDef 0x1: TypeRef 0x2: TypeSpec We could therefore compress the 4-byte token that would otherwise be needed into a coded token of type TypeDefOrRef. For each type of coded token, the least significant bits encode the table the token points to, and the rest of the bits encode the RID within that table. We can work out whether each type of coded token needs 2 or 4 bytes to represent it by working out whether the maximum RID of every table that the coded token type can point to will fit in the space available. The space available for the RID depends on the type of coded token; a TypeOrMethodDef coded token only needs 1 bit to specify the table, leaving 15 bits available for the RID before a 4-byte representation is needed, whereas a HasCustomAttribute coded token can point to one of 18 different tables, and so needs 5 bits to specify the table, only leaving 11 bits for the RID before 4 bytes are needed to represent that coded token type. For example, a 2-byte TypeDefOrRef coded token with the value 0x0321 has the following bit pattern: 0 3 2 1 0000 0011 0010 0001 The first two bits specify the table - TypeRef; the other bits specify the RID. Because we've used the first two bits, we've got to shift everything along two bits: 000000 1100 1000 This gives us a RID of 0xc8. If any one of the TypeDef, TypeRef or TypeSpec tables had more than 16383 rows (2^14 - 1), then 4 bytes would need to be used to represent all TypeDefOrRef coded tokens throughout the metadata tables. Lists The third representation we need to consider is 1-to-many references; each TypeDef refers to a list of FieldDef and MethodDef belonging to that type. If we were to specify every FieldDef and MethodDef individually then each TypeDef would be very large and a variable size, which isn't ideal. There is a way of specifying a list of references without explicitly specifying every item; if we order the MethodDef and FieldDef tables by the owning type, then the field list and method list in a TypeDef only have to be a single RID pointing at the first FieldDef or MethodDef belonging to that type; the end of the list can be inferred by the field list and method list RIDs of the next row in the TypeDef table. Going back to the TypeDef If we have a look back at the definition of a TypeDef, we end up with the following reprensentation for each row: Flags - always 4 bytes Name - a #Strings heap offset. Namespace - a #Strings heap offset. Extends - a TypeDefOrRef coded token. FieldList - a single RID to the FieldDef table. MethodList - a single RID to the MethodDef table. So, depending on the number of entries in the heaps and tables within the assembly, the rows in the TypeDef table can be as small as 14 bytes, or as large as 24 bytes. Now we've had a look at how information is encoded within the metadata tables, in the next post we can see how they are arranged on disk.

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