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  • Samba smbtree No output; failed to retrieve share list

    - by TomKat
    I'm using Ubuntu 12.10 on two machines, one laptop & one desktop. Faced the same problem when I used 12.04. When I try connecting to the other machine using 'Connect to Server', I give the correct user & workgroup details, but the system displays 'failed to retrieve server list' I've tried editing /etc/samba/smb.conf file to: name resolve order = lmhosts host wins bcast I also added the other machine to /etc/hosts But, nothing worked. The output of smbtree is naveen@tomkat:~$ smbtree Enter naveen's password: naveen@tomkat:~$ Used sources to solve problem myself: "Failed to retrieve share list from server" error when browsing a share with Nautilus http://ubuntuforums.org/showthread.php?t=1114038 All help will be appreciated. Thanks. UPDATE: After 'purging' samba and all its components (incl all config files), and reinstall, sharing workes in one direction (from Laptop to Desktop) but when I attempt to use the Desktop as server, same problem is still faced. UPDATE 2 dpkg -l|grep samba output: naveen@tomkat:~$ sudo dpkg -l|grep samba [sudo] password for naveen: ii libcrypt-smbhash-perl 0.12-3 all generate LM/NT hash of a password for samba ii samba 2:3.6.6-3ubuntu5 i386 SMB/CIFS file, print, and login server for Unix ii samba-common 2:3.6.6-3ubuntu5 all common files used by both the Samba server and client ii samba-common-bin 2:3.6.6-3ubuntu5 i386 common files used by both the Samba server and client

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  • Upgrade Your Existing BI Publisher 11g (11.1.1.3) to 11.1.1.5

    - by Kan Nishida
    It’s already more than a month now since BI Publisher 11.1.1.5 was released at beginning of May. Have you already tried out many of the great new features? If you are already running on the first version of BI Publisher 11g (11.1.1.3) you might wonder how to upgrade the existing BI Publisher to the 11.1.1.5 version. There are two ways to do this, one is ‘Out-Place’ and another is ‘In-Place’. The ‘Out-Place’ would be quite simple. Basically you will need to install the whole BI or just BI Publisher standalone R11.1.1.5 at a different location then you can switch the catalog to the existing one so that all the reports will be there in the new 11.1.1.5 environment. But sometimes things are not that simple, you might have some custom applications or configuration on the original environment and you want to keep all of them with the upgraded environment. For such scenarios, there is the ‘In-Place’ upgrade, which overrides on top of the original environment only the parts relevant for BI and BI Publisher, and that’s what I’m going to talk about today. Here is the basic steps of the ‘In-Place’ upgrade. Upgrade WebLogic Server to 10.3.5 Upgrade BI System to 11.1.1.5 Upgrade Database Schema Re-register BI Components Upgrade FMW (Fusion Middleware) Configuration Upgrade BI Catalog There is a section that talks about this upgrade from 11.1.1.3 to 11.1.1.5 as part of the overall upgrade document. But I hope my blog post summarized it and made it simple for you to cover only what’s necessary. Upgrade Document: http://download.oracle.com/docs/cd/E21764_01/bi.1111/e16452/bi_plan.htm#BABECJJH Before You Start Stop BI System and Backup I can’t emphasize enough, but before you start PLEASE make sure you take a backup of the existing environments first. You want to stop all WebLogic Servers, Node Manager, OPMN, and OPMN-managed system components that are part of your Oracle BI domains. If you’re on Windows you can do this by simply selecting ‘Stop BI Services’ menu. Then backup the whole system. Upgrade WebLogic Server to 10.3.5 Download WebLogic Server 10.3.5 Upgrade Installer With BI 11.1.1.3 installation your WebLogic Server (WLS) is 10.3.3 and you need to upgrade this to 10.3.5 before upgrading the BI part. In order to upgrade you will need this 10.3.5 upgrade version of WLS, which you can download from our support web site (https://support.oracle.com) You can find the detail information about the installation and the patch numbers for the WLS upgrade installer on this document. Just for your short cut, if you are running on Windows or Linux (x86) here is the patch number for your platform. Windows 32 bit: 12395517: Linux: 12395517 Upgrade WebLogic Server 1. After unzip the downloaded file, launch wls1035_upgrade_win32.exe if you’re on Windows. 2. Accept all the default values and keep ‘Next’ till end, and start the upgrade. Once the upgrade process completes you’ll see the following window. Now let’s move to the BI upgrade. Upgrade BI Platform to 11.1.1.5 with Software Only Install Download BI 11.1.1.5 You can download the 11.1.1.5 version from our OTN page for your evaluation or development. For the production use it’s recommended to download from eDelivery. 1. Launch the installer by double click ‘setup.exe’ (for Windows) 2. Select ‘Software Only Install’ option 3. Select your original Oracle Home where you installed BI 11.1.1.3. 4. Click ‘Install’ button to start the installation. And now the software part of the BI has been upgraded to 11.1.1.5. Now let’s move to the database schema upgrade. Upgrade Database Schema with Patch Assistant You need to upgrade the BIPLATFORM and MDS Schemas. You can use the Patch Assistant utility to do this, and here is an example assuming you’ve created the schema with ‘DEV’ prefix, otherwise change it with yours accordingly. Upgrade BIPLATFORM schema (if you created this schema with DEV_ prev) psa.bat -dbConnectString localhost:1521:orcl -dbaUserName sys -schemaUserName DEV_BIPLATFORM Upgrade MDS schema (if you created this schema with DEV_ prev) psa.bat -dbConnectString localhost:1521:orcl -dbaUserName sys -schemaUserName DEV_MDS Re-register BI System components Now you need to re-register your BI system components such as BI Server, BI Presentation Server, etc to the Fusion Middleware system. You can do this by running ‘upgradenonj2eeapp.bat (or .sh)’ command, which can be found at %ORACLE_HOME%/opmn/bin. Before you run, you need to start the WLS Server and make sure your WLS environment is not locked. If it’s locked then you need to release the system from the Fusion Middleware console before you run the following command. Here is the syntax for the ‘upgradenonj2eeapp.bat (or .sh) command.  upgradenonj2eeapp.bat    -oracleInstance Instance_Home_Location    -adminHost WebLogic_Server_Host_Name    -adminPort administration_server_port_number    -adminUsername administration_server_user And here is an example: cd %BI_HOME%\opmn\bin upgradenonj2eeapp.bat -oracleInstance C:\biee11\instances\instance1 -adminHost localhost -adminPort 7001 -adminUsername weblogic Upgrade Fusion Middleware Configuration There are a couple things on the Fusion Middleware need to be upgraded for the BI system to work. Here is a list of the components to upgrade. Upgrade Shared Library (JRF) Upgrade Fusion Middleware Security (OPSS) Upgrade Code Grants Upgrade OWSM Policy Repository Before moving forward, you need to stop the WebLogic Server. Here is an example. cd %MW_HOME%user_projects\domains\bifoundation_domain\binstopWebLogic.cmd And, let’s start with ‘Upgrade Shared Library (JRF)’. Upgrade Shared Library (JRF) You can use updateJRF() WLST command to upgrade the shared libraries in your domain. Before you do this, you need to stop all running instances, Managed Servers, Administration Server, and Node Manager in the domain. Here is an example of the ‘upgradeJRF()’ command: cd %MW_HOME%\oracle_common\common\bin wlst.cmd upgradeJRF('C:/biee11/user_projects/domains/bifoundation_domain') Upgrade Fusion Middleware Security (OPSS) This step is to upgrade the Fusion Middleware security piece. You can use ‘upgradeOpss()’ WLST command. Here is a syntax for the command. upgradeOpss(jpsConfig="existing_jps_config_file", jaznData="system_jazn_data_file") The ‘existing jps-config.xml file can be found under %DOMAIN_HOME%/config/fmwconfig/jps-config.xml and the ‘system_jazn_data_file’ can be found under %MW_HOME%/oracle_common/modules/oracle.jps_11.1.1/domain_config/system-jazn-data.xml. And here is an example: cd %MW_HOME%\oracle_common\common\bin wlst.cmd upgradeOpss(jpsConfig="c:/biee11/user_projects/domains/bifoundation_domain/config/fmwconfig/jps-config.xml", jaznData="c:/biee11/oracle_common/modules/oracle.jps_11.1.1/domain_config/system-jazn-data.xml") exit() Upgrade Code Grants for Oracle BI Domain And this is the last step for the Fusion Middleware platform upgrade task. You need to run this python script ‘bi-upgrade.py‘ script to configure the code grants necessary to ensure that SSL works correctly for Oracle BI. However, even if you don’t use SSL, you still need to run this script. And if you have multiple BI domains (Enterprise deployment) then you need to run this on each domain. Here is an example: cd %MW_HOME%\oracle_common\common\bin wlst c:\biee11\Oracle_BI1\bin\bi-upgrade.py --bioraclehome c:\biee11\Oracle_BI1 --domainhome c:\biee11\user_projects\domains\bifoundation_domain Upgrade OWSM Policy Repository This is to upgrade OWSM (Oracle Web Service Manager) policy repository, you can use WLST command ‘upgradeWSMPolicyRepository()’. In order to run this command you need to have your WebLogic Server up-and-running. Here is an example. cd %MW_HOME%user_projects\domains\bifoundation_domain\binstopWebLogic.cmd cd %MW_HOME%\oracle_common\common\bin wlst.cmd connect ('weblogic','welcome1','t3://localhost:7001') upgradeWSMPolicyRepository() exit() Upgrade BI Catalogs This step is required only when you have your BI Publisher integrated with BIEE. If your BI Publisher is deployed as a standalone then you don’t need to follow this step. Now finally, you can upgrade the BI catalog. This won’t upgrade your BI Publisher reports themselves, but it just upgrades some attributes information inside the catalog. Before you do this upgrade, make sure the BI system components are not running. You can check the status by the command below. opmnctl status You can do the upgrade by updating a configuration file ‘instanceconfig.xml’, which can be found at %BI_HOME%\instances\instance1\config\coreapplication_obips1, and change the value of ‘UpgradeAndExit’ to be ‘true’. Here is an example: <ps:Catalog xmlns:ps="oracle.bi.presentation.services/config/v1.1"> <ps:UpgradeAndExit>true</ps:UpgradeAndExit> </ps:Catalog> After you made the change and save the file, you need to start the BI Presentation Server. This time you want to start only the BI Presentation Server instead of starting all the servers. You can use ‘opmnctl’ to do so, and here is an example. cd %ORACLE_INSTANCE%\bin opmnctl startproc ias-component=coreapplication_obips1 This would upgrade your BI Catalog to be 11.1.1.5. After the catalog is updated, you can stop the BI Presentation Server so that you can modify the instanceconfig.xml file again to revert the upgradeAndExit value back to ‘false’. Start Explore BI Publisher 11.1.1.5 After all the above steps, you can start all the BI Services, access to the same URL, now you have your BI Publisher and/or BI 11.1.1.5 in your hands. Have fun exploring all the new features of R11.1.1.5!

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  • Queued Loadtest to remove Concurrency issues using Shared Data Service in OpenScript

    - by stefan.thieme(at)oracle.com
    Queued Processing to remove Concurrency issues in Loadtest ScriptsSome scripts act on information returned by the server, e.g. act on first item in the returned list of pending tasks/actions. This may lead to concurrency issues if the virtual users simulated in a load test scenario are not synchronized in some way.As the load test cases should be carried out in a comparable and straight forward manner simply cancel a transaction in case a collision occurs is clearly not an option. In case you increase the number of virtual users this approach would lead to a high number of requests for the early steps in your transaction (e.g. login, retrieve list of action points, assign an action point to the virtual user) but later steps would be rarely visited successfully or at all, depending on the application logic.A way to tackle this problem is to enqueue the virtual users in a Shared Data Service queue. Only the first virtual user in this queue will be allowed to carry out the critical steps (retrieve list of action points, assign an action point to the virtual user) in your transaction at any one time.Once a virtual user has passed the critical path it will dequeue himself from the head of the queue and continue with his actions. This does theoretically allow virtual users to run in parallel all steps of the transaction which are not part of the critical path.In practice it has been seen this is rarely the case, though it does not allow adding more than N users to perform a transaction without causing delays due to virtual users waiting in the queue. N being the time of the total transaction divided by the sum of the time of all critical steps in this transaction.While this problem can be circumvented by allowing multiple queues to act on individual segments of the list of actions, e.g. per country filter, ends with 0..9 filter, etc.This would require additional handling of these additional queues of slots for the virtual users at the head of the queue in order to maintain the mutually exclusive access to the first element in the list returned by the server at any one time of the load test. Such an improved handling of multiple queues and/or multiple slots is above the subject of this paper.Shared Data Services Pre-RequisitesStart WebLogic Server to host Shared Data ServicesYou will have to make sure that your WebLogic server is installed and started. Shared Data Services may not work if you installed only the minimal installation package for OpenScript. If however you installed the default package including OLT and OTM, you may follow the instructions below to start and verify WebLogic installation.To start the WebLogic Server deployed underneath of Oracle Load Testing and/or Oracle Test Manager you can go to your Start menu, Oracle Application Testing Suite and select the Restart Oracle Application Testing Suite Application Service entry from the Tools submenu.To verify the service has been started you can run the Microsoft Management Console for Services by Selecting Run from the Start Menu and entering services.msc. Look for the entry that reads Oracle Application Testing Suite Application Service, once it has changed it status from Starting to Started you can proceed to verify the login. Please note that this may take several minutes, I would say up to 10 minutes depending on the strength of your CPU horse-power.Verify WebLogic Server user credentialsYou will have to make sure that your WebLogic Server is installed and started. Next open the Oracle WebLogic Server Adminstration Console on http://localhost:8088/console.It may take a while until the application is deployed and started. It may display the following until the Administration Console has been deployed on the fly.Afterwards you can login using the username oats and the password that you selected during install time for your Application Testing Suite administrative purposes.This will bring up the Home page of you WebLogic Server. You have actually verified that you are able to login with these credentials already. However if you want to check the details, navigate to Security Realms, myrealm, Users and Groups tab.Here you could add users to your WebLogic Server which could be used in the later steps. Details on the Groups required for such a custom user to work are exceeding this quick overview and have to be selected with the WebLogic Server Adminstration Guide in mind.Shared Data Services pre-requisites for Load testingOpenScript Preferences have to be set to enable Encryption and provide a default Shared Data Service Connection for Playback.These are pre-requisites you want to use for load testing with Shared Data Services.Please note that the usage of the Connection Parameters (individual directive in the script) for Shared Data Services did not playback reliably in the current version 9.20.0370 of Oracle Load Testing (OLT) and encryption of credentials still seemed to be mandatory as well.General Encryption settingsSelect OpenScript Preferences from the View menu and navigate to the General, Encryption entry in the tree on the left. Select the Encrypt script data option from the list and enter the same password that you used for securing your WebLogic Server Administration Console.Enable global shared data access credentialsSelect OpenScript Preferences from the View menu and navigate to the Playback, Shared Data entry in the tree on the left. Enable the global shared data access credentials and enter the Address, User name and Password determined for your WebLogic Server to host Shared Data Services.Please note, that you may want to replace the localhost in Address with the hosts realname in case you plan to run load tests with Loadtest Agents running on remote systems.Queued Processing of TransactionsEnable Shared Data Services Module in Script PropertiesThe Shared Data Services Module has to be enabled for each Script that wants to employ the Shared Data Service Queue functionality in OpenScript. It can be enabled under the Script menu selecting Script Properties. On the Script Properties Dialog select the Modules section and check Shared Data to enable Shared Data Service Module for your script. Checking the Shared Data Services option will effectively add a line to your script code that adds the sharedData ScriptService to your script class of IteratingVUserScript.@ScriptService oracle.oats.scripting.modules.sharedData.api.SharedDataService sharedData;Record your scriptRecord your script as usual and then add the following things for Queue handling in the Initialize code block, before the first step and after the last step of your critical path and in the Finalize code block.The java code to be added at individual locations is explained in the following sections in full detail.Create a Shared Data Queue in InitializeTo create a Shared Data Queue go to the Java view of your script and enter the following statements to the initialize() code block.info("Create queueA with life time of 120 minutes");sharedData.createQueue("queueA", 120);This will create an instantiation of the Shared Data Queue object named queueA which is maintained for upto 120 minutes.If you want to use the code for multiple scripts, make sure to use a different queue name for each one here and in the subsequent steps. You may even consider to use a dynamic queueName based on filters of your result list being concurrently accessed.Prepare a unique id for each IterationIn order to keep track of individual virtual users in our queue we need to create a unique identifier from the virtual user id and the used username right after retrieving the next record from our databank file.getDatabank("Usernames").getNextDatabankRecord();getVariables().set("usernameValue1","VU_{{@vuid}}_{{@iterationnum}}_{{db.Usernames.Username}}_{{@timestamp}}_{{@random(10000)}}");String usernameValue = getVariables().get("usernameValue1");info("Now running virtual user " + usernameValue);As you can see from the above code block, we have set the OpenScript variable usernameValue1 to VU_{{@vuid}}_{{@iterationnum}}_{{db.Usernames.Username}}_{{@timestamp}}_{{@random(10000)}} which is a concatenation of the virtual user id and the iterationnumber for general uniqueness; as well as the username from our databank, the timestamp and a random number for making it further unique and ease spotting of errors.Not all of these fields are actually required to make it really unique, but adding the queue name may also be considered to help troubleshoot multiple queues.The value is then retrieved with the getVariables.get() method call and assigned to the usernameValue String used throughout the script.Please note that moving the getDatabank("Usernames").getNextDatabankRecord(); call to the initialize block was later considered to remove concurrency of multiple virtual users running with the same userid and therefor accessing the same "My Inbox" in step 6. This will effectively give each virtual user a userid from the databank file. Make sure you have enough userids to remove this second hurdle.Enqueue and attend Queue before Critical PathTo maintain the right order of virtual users being allowed into the critical path of the transaction the following pseudo step has to be added in front of the first critical step. In the case of this example this is right in front of the step where we retrieve the list of actions from which we select the first to be assigned to us.beginStep("[0] Waiting in the Queue", 0);{info("Enqueued virtual user " + usernameValue + " at the end of queueA");sharedData.offerLast("queueA", usernameValue);info("Wait until the user is the first in queueA");String queueValue1 = null;do {// we wait for at least 0.7 seconds before we check the head of the// queue. This is the time it takes one user to move through the// critical path, i.e. pass steps [5] Enter country and [6] Assign// to meThread.sleep(700);queueValue1 = (String) sharedData.peekFirst("queueA");info("The first user in queueA is currently: '" + queueValue1 + "' " + queueValue1.getClass() + " length " + queueValue1.length() );info("The current user is '"+ usernameValue + "' " + usernameValue.getClass() + " length " + usernameValue.length() + ": indexOf " + usernameValue.indexOf(queueValue1) + " equals " + usernameValue.equals(queueValue1) );} while ( queueValue1.indexOf(usernameValue) < 0 );info("Now the user is the first in queueA");}endStep();This will enqueue the username to the tail of our Queue. It will will wait for at least 700 milliseconds, the time it takes for one user to exit the critical path and then compare the head of our queue with it's username. This last step will be repeated while the two are not equal (indexOf less than zero). If they are equal the indexOf will yield a value of zero or larger and we will perform the critical steps.Dequeue after Critical PathAfter the virtual user has left the critical path and complete its last step the following code block needs to dequeue the virtual user. In the case of our example this is right after the action has been actually assigned to the virtual user. This will allow the next virtual user to retrieve the list of actions still available and in turn let him make his selection/assignment.info("Get and remove the current user from the head of queueA");String pollValue1 = (String) sharedData.pollFirst("queueA");The current user is removed from the head of the queue. The next one will now be able to match his username against the head of the queue.Clear and Destroy Queue for FinishWhen the script has completed, it should clear and destroy the queue. This code block can be put in the finish block of your script and/or in a separate script in order to clear and remove the queue in case you have spotted an error or want to reset the queue for some reason.info("Clear queueA");sharedData.clearQueue("queueA");info("Destroy queueA");sharedData.destroyQueue("queueA");The users waiting in queueA are cleared and the queue is destroyed. If you have scripts still executing they will be caught in a loop.I found it better to maintain a separate Reset Queue script which contained only the following code in the initialize() block. I use to call this script to make sure the queue is cleared in between multiple Loadtest runs. This script could also even be added as the first in a larger scenario, which would execute it only once at very start of the Loadtest and make sure the queues do not contain any stale entries.info("Create queueA with life time of 120 minutes");sharedData.createQueue("queueA", 120);info("Clear queueA");sharedData.clearQueue("queueA");This will create a Shared Data Queue instance of queueA and clear all entries from this queue.Monitoring QueueWhile creating the scripts it was useful to monitor the contents, i.e. the current first user in the Queue. The following code block will make sure the Shared Data Queue is accessible in the initialize() block.info("Create queueA with life time of 120 minutes");sharedData.createQueue("queueA", 120);In the run() block the following code will continuously monitor the first element of the Queue and write an informational message with the current username Value to the Result window.info("Monitor the first users in queueA");String queueValue1 = null;do {queueValue1 = (String) sharedData.peekFirst("queueA");if (queueValue1 != null)info("The first user in queueA is currently: '" + queueValue1 + "' " + queueValue1.getClass() + " length " + queueValue1.length() );} while ( true );This script can be run from OpenScript parallel to a loadtest performed by the Oracle Load Test.However it is not recommend to run this in a production loadtest as the performance impact is unknown. Accessing the Queue's head with the peekFirst() method has been reported with about 2 seconds response time by both OpenScript and OTL. It is advised to log a Service Request to see if this could be lowered in future releases of Application Testing Suite, as the pollFirst() and even offerLast() writing to the tail of the Queue usually returned after an average 0.1 seconds.Debugging QueueWhile debugging the scripts the following was useful to remove single entries from its head, i.e. the current first user in the Queue. The following code block will make sure the Shared Data Queue is accessible in the initialize() block.info("Create queueA with life time of 120 minutes");sharedData.createQueue("queueA", 120);In the run() block the following code will remove the first element of the Queue and write an informational message with the current username Value to the Result window.info("Get and remove the current user from the head of queueA");String pollValue1 = (String) sharedData.pollFirst("queueA");info("The first user in queueA was currently: '" + pollValue1 + "' " + pollValue1.getClass() + " length " + pollValue1.length() );ReferencesOracle Functional Testing OpenScript User's Guide Version 9.20 [E15488-05]Chapter 17 Using the Shared Data Modulehttp://download.oracle.com/otn/nt/apptesting/oats-docs-9.21.0030.zipOracle Fusion Middleware Oracle WebLogic Server Administration Console Online Help 11g Release 1 (10.3.4) [E13952-04]Administration Console Online Help - Manage users and groupshttp://download.oracle.com/docs/cd/E17904_01/apirefs.1111/e13952/taskhelp/security/ManageUsersAndGroups.htm

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  • How do I pin a particular MySQL version to avoid unnecessary upgrades?

    - by asparagino
    I'm running a MySQL server, and want to keep it up to date with regular apt-upgrades. I don't want this to cause MySQL to upgrade unless I'm doing it during scheduled downtime! How do I alter my apt-preferences so that this won't happen? I've tried adding this to a file as /etc/apt/preferences.d/pin-mysql Package: mysql-client-5.1 Pin: version 5.1.41-3ubuntu12.7 Pin-Priority: 1001 Package: mysql-client-core-5.1 Pin: version 5.1.41-3ubuntu12.7 Pin-Priority: 1001 Package: mysql-common Pin: version 5.1.41-3ubuntu12.7 Pin-Priority: 1001 Package: mysql-server Pin: version 5.1.41-3ubuntu12.7 Pin-Priority: 1001 Package: mysql-server-5.1 Pin: version 5.1.41-3ubuntu12.7 Pin-Priority: 1001 Package: mysql-server-core-5.1 Pin: version 5.1.41-3ubuntu12.7 Pin-Priority: 1001 That then states the packages are pinned with "apt-cache policy" outputting: ... all package sources here 500 http://security.ubuntu.com/ubuntu/ lucid-security/universe Packages release v=10.04,o=Ubuntu,a=lucid-security,n=lucid,l=Ubuntu,c=universe origin security.ubuntu.com 500 http://security.ubuntu.com/ubuntu/ lucid-security/restricted Packages release v=10.04,o=Ubuntu,a=lucid-security,n=lucid,l=Ubuntu,c=restricted origin security.ubuntu.com ... etc Pinned packages: mysql-server -> 5.1.41-3ubuntu12.7 mysql-server-core-5.1 -> 5.1.41-3ubuntu12.7 mysql-client-core-5.1 -> 5.1.41-3ubuntu12.7 mysql-common -> 5.1.41-3ubuntu12.7 mysql-server-5.1 -> 5.1.41-3ubuntu12.7 mysql-client-5.1 -> 5.1.41-3ubuntu12.7 However... running aptitude safe-upgrade just updated MySQL... what am I doing wrong?

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  • Fun with Aggregates

    - by Paul White
    There are interesting things to be learned from even the simplest queries.  For example, imagine you are given the task of writing a query to list AdventureWorks product names where the product has at least one entry in the transaction history table, but fewer than ten. One possible query to meet that specification is: SELECT p.Name FROM Production.Product AS p JOIN Production.TransactionHistory AS th ON p.ProductID = th.ProductID GROUP BY p.ProductID, p.Name HAVING COUNT_BIG(*) < 10; That query correctly returns 23 rows (execution plan and data sample shown below): The execution plan looks a bit different from the written form of the query: the base tables are accessed in reverse order, and the aggregation is performed before the join.  The general idea is to read all rows from the history table, compute the count of rows grouped by ProductID, merge join the results to the Product table on ProductID, and finally filter to only return rows where the count is less than ten. This ‘fully-optimized’ plan has an estimated cost of around 0.33 units.  The reason for the quote marks there is that this plan is not quite as optimal as it could be – surely it would make sense to push the Filter down past the join too?  To answer that, let’s look at some other ways to formulate this query.  This being SQL, there are any number of ways to write logically-equivalent query specifications, so we’ll just look at a couple of interesting ones.  The first query is an attempt to reverse-engineer T-SQL from the optimized query plan shown above.  It joins the result of pre-aggregating the history table to the Product table before filtering: SELECT p.Name FROM ( SELECT th.ProductID, cnt = COUNT_BIG(*) FROM Production.TransactionHistory AS th GROUP BY th.ProductID ) AS q1 JOIN Production.Product AS p ON p.ProductID = q1.ProductID WHERE q1.cnt < 10; Perhaps a little surprisingly, we get a slightly different execution plan: The results are the same (23 rows) but this time the Filter is pushed below the join!  The optimizer chooses nested loops for the join, because the cardinality estimate for rows passing the Filter is a bit low (estimate 1 versus 23 actual), though you can force a merge join with a hint and the Filter still appears below the join.  In yet another variation, the < 10 predicate can be ‘manually pushed’ by specifying it in a HAVING clause in the “q1” sub-query instead of in the WHERE clause as written above. The reason this predicate can be pushed past the join in this query form, but not in the original formulation is simply an optimizer limitation – it does make efforts (primarily during the simplification phase) to encourage logically-equivalent query specifications to produce the same execution plan, but the implementation is not completely comprehensive. Moving on to a second example, the following query specification results from phrasing the requirement as “list the products where there exists fewer than ten correlated rows in the history table”: SELECT p.Name FROM Production.Product AS p WHERE EXISTS ( SELECT * FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID HAVING COUNT_BIG(*) < 10 ); Unfortunately, this query produces an incorrect result (86 rows): The problem is that it lists products with no history rows, though the reasons are interesting.  The COUNT_BIG(*) in the EXISTS clause is a scalar aggregate (meaning there is no GROUP BY clause) and scalar aggregates always produce a value, even when the input is an empty set.  In the case of the COUNT aggregate, the result of aggregating the empty set is zero (the other standard aggregates produce a NULL).  To make the point really clear, let’s look at product 709, which happens to be one for which no history rows exist: -- Scalar aggregate SELECT COUNT_BIG(*) FROM Production.TransactionHistory AS th WHERE th.ProductID = 709;   -- Vector aggregate SELECT COUNT_BIG(*) FROM Production.TransactionHistory AS th WHERE th.ProductID = 709 GROUP BY th.ProductID; The estimated execution plans for these two statements are almost identical: You might expect the Stream Aggregate to have a Group By for the second statement, but this is not the case.  The query includes an equality comparison to a constant value (709), so all qualified rows are guaranteed to have the same value for ProductID and the Group By is optimized away. In fact there are some minor differences between the two plans (the first is auto-parameterized and qualifies for trivial plan, whereas the second is not auto-parameterized and requires cost-based optimization), but there is nothing to indicate that one is a scalar aggregate and the other is a vector aggregate.  This is something I would like to see exposed in show plan so I suggested it on Connect.  Anyway, the results of running the two queries show the difference at runtime: The scalar aggregate (no GROUP BY) returns a result of zero, whereas the vector aggregate (with a GROUP BY clause) returns nothing at all.  Returning to our EXISTS query, we could ‘fix’ it by changing the HAVING clause to reject rows where the scalar aggregate returns zero: SELECT p.Name FROM Production.Product AS p WHERE EXISTS ( SELECT * FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID HAVING COUNT_BIG(*) BETWEEN 1 AND 9 ); The query now returns the correct 23 rows: Unfortunately, the execution plan is less efficient now – it has an estimated cost of 0.78 compared to 0.33 for the earlier plans.  Let’s try adding a redundant GROUP BY instead of changing the HAVING clause: SELECT p.Name FROM Production.Product AS p WHERE EXISTS ( SELECT * FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY th.ProductID HAVING COUNT_BIG(*) < 10 ); Not only do we now get correct results (23 rows), this is the execution plan: I like to compare that plan to quantum physics: if you don’t find it shocking, you haven’t understood it properly :)  The simple addition of a redundant GROUP BY has resulted in the EXISTS form of the query being transformed into exactly the same optimal plan we found earlier.  What’s more, in SQL Server 2008 and later, we can replace the odd-looking GROUP BY with an explicit GROUP BY on the empty set: SELECT p.Name FROM Production.Product AS p WHERE EXISTS ( SELECT * FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY () HAVING COUNT_BIG(*) < 10 ); I offer that as an alternative because some people find it more intuitive (and it perhaps has more geek value too).  Whichever way you prefer, it’s rather satisfying to note that the result of the sub-query does not exist for a particular correlated value where a vector aggregate is used (the scalar COUNT aggregate always returns a value, even if zero, so it always ‘EXISTS’ regardless which ProductID is logically being evaluated). The following query forms also produce the optimal plan and correct results, so long as a vector aggregate is used (you can probably find more equivalent query forms): WHERE Clause SELECT p.Name FROM Production.Product AS p WHERE ( SELECT COUNT_BIG(*) FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY () ) < 10; APPLY SELECT p.Name FROM Production.Product AS p CROSS APPLY ( SELECT NULL FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY () HAVING COUNT_BIG(*) < 10 ) AS ca (dummy); FROM Clause SELECT q1.Name FROM ( SELECT p.Name, cnt = ( SELECT COUNT_BIG(*) FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY () ) FROM Production.Product AS p ) AS q1 WHERE q1.cnt < 10; This last example uses SUM(1) instead of COUNT and does not require a vector aggregate…you should be able to work out why :) SELECT q.Name FROM ( SELECT p.Name, cnt = ( SELECT SUM(1) FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID ) FROM Production.Product AS p ) AS q WHERE q.cnt < 10; The semantics of SQL aggregates are rather odd in places.  It definitely pays to get to know the rules, and to be careful to check whether your queries are using scalar or vector aggregates.  As we have seen, query plans do not show in which ‘mode’ an aggregate is running and getting it wrong can cause poor performance, wrong results, or both. © 2012 Paul White Twitter: @SQL_Kiwi email: [email protected]

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  • Practical Approaches to increasing Virtualization Density-Part 1

    - by Girish Venkat
    Happy New year everyone!. Let me kick start the year off by talking about Virtualization density.  What is it?The number of virtual servers that a physical server can support and it's increase from the prior physical infrastructure as a percentage. Why is it important?This is important because the density should be indicative of how well the server is getting consumed?So what is wrong ?Virtualization density fails to convey the "Real usage" of a server.  Most of the hypervisor based O/S Virtualization  evangelists take pride in the fact that they are now running a Virtual Server farm of X machines compared to a Physical server farm of Y (with Y less than X obviously). The real question is - has your utilization of the server really increased or not.  In an internal study that was conducted by one of the top financial institution - the utilization of servers only went up by 15% from 30 to 45. So, this really means that just by increasing virtualization density one will not be achieving the goal of using up the servers in their server farm better.  I will write about what the possible approaches are to increase virtualization density in the next entry. 

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  • Ubuntu 13.10 Installing MariaDB

    - by Ecaz
    I have tried everything to install MariaDB on this clean Ubuntu installation but I keep getting this error, Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: mariadb-server : Depends: mariadb-server-5.5 (= 5.5.33a+maria-1~saucy) but it is not going to be installed E: Unable to correct problems, you have held broken packages. I have followed this guide to try and install it, http://www.unixmen.com/install-lemp-server-nginx-mysql-mariadb-php-ubuntu-13-10-server/ And I have also followed the "official" guide on the MariaDB downloads page for 13.10 https://downloads.mariadb.org/mariadb/repositories/ But nothing seems to be working. Edit 1 I have tried both How do I resolve unmet dependencies? and How to install MariaDB? but it still gives me the error I posted above. It's a fresh Ubuntu install with hardly anything installed. Edit 2 All the check boxes are ticket in Updates. I ran: sudo apt-get update && sudo apt-get -f install mariadb-server-5.5"=5.5.33a+maria-1~saucy" And it gave me this error: The following packages have unmet dependencies: mariadb-server-5.5 : Depends: mariadb-client-5.5 (>= 5.5.33a+maria-1~saucy) but it is not going to be installed Depends: mariadb-server-core-5.5 (>= 5.5.33a+maria-1~saucy) but it is not going to be installed E: Unable to correct problems, you have held broken packages.

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  • Checking if your SIMPLE databases need a log backup

    - by Fatherjack
    Hopefully you have read the blog by William Durkin explaining why your SIMPLE databases need a log backup in some cases. There is a SQL Server bug that means in some cases databases are marked as being in SIMPLE RECOVERY but have a log wait type that shows they are not properly configured. Please read his blog for the full explanation and a great description of how to reproduce the issue. As part of our (William happens to be my Boss) work to recover our affected databases I wrote this small PowerShell script to quickly check our servers for databases that needed the attention that William details.  cls $Servers = “Server01″,”Server02″,”etc”,”etc” foreach($Server in $Servers){ write-host “************” $server “****************”     $server = New-Object Microsoft.sqlserver.management.smo.server $Server     foreach($db in $Server.databases){         $db | where {$_.RecoveryModel -eq “Simple” -and $_.logreusewaitstatus -ne “nothing”} | select name, LogReuseWaitStatus     } } If you get any results from this query then you should consult Williams blog for the details on what action you should take. This script does give out false positives if in some circumstances depending on how busy your databases are. Hopefully this will let you check your servers quickly and if you find any problems you can reference Williams blog to understand what you need to do.

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  • Ubuntu 13.10 Installing MariaDB when Apt reports MariaDB has unmet dependencies or broken packages

    - by Ecaz
    I have tried everything to install MariaDB on this clean Ubuntu installation but I keep getting this error, Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: mariadb-server : Depends: mariadb-server-5.5 (= 5.5.33a+maria-1~saucy) but it is not going to be installed E: Unable to correct problems, you have held broken packages. I have followed this guide to try and install it, http://www.unixmen.com/install-lemp-server-nginx-mysql-mariadb-php-ubuntu-13-10-server/ And I have also followed the "official" guide on the MariaDB downloads page for 13.10 https://downloads.mariadb.org/mariadb/repositories/ But nothing seems to be working. Edit 1 I have tried both How do I resolve unmet dependencies? and How to install MariaDB? but it still gives me the error I posted above. It's a fresh Ubuntu install with hardly anything installed. Edit 2 All the check boxes are ticket in Updates. I ran: sudo apt-get update && sudo apt-get -f install mariadb-server-5.5"=5.5.33a+maria-1~saucy" And it gave me this error: The following packages have unmet dependencies: mariadb-server-5.5 : Depends: mariadb-client-5.5 (>= 5.5.33a+maria-1~saucy) but it is not going to be installed Depends: mariadb-server-core-5.5 (>= 5.5.33a+maria-1~saucy) but it is not going to be installed E: Unable to correct problems, you have held broken packages.

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  • Building Single Page Apps on the Microsoft Stack

    - by Stephen.Walther
    Thank you everyone who came to my talk last night on Building Single Page Apps on the Microsoft Stack. I’ve attached the slides and code samples below. Here’s a quick summary of the talk. I argued that Single Page Apps are better than traditional Server Side Apps because: Single Page Apps are Stateful – In a traditional server-side app, whenever you navigate to a new page, all of your previous state is lost. It is like rebooting your computer whenever you perform any action In a Single Page App, Your Presentation Layer is Not Miles Away – In a traditional server-side app, because everything happens on the server, your presentation layer is separated from the user by space and time. In a Single Page App, the presentation layer is in the browser and not the server (which is the right place for a presentation layer). A Single Page App Respects the Web – It is easier to take advantage of HTML5 and related standards when building a Single Page App. Next, I recommended using the following four technologies when building a web application: Knockout – This is how you create your presentation layer. ASP.NET Web API – This is how you expose JSON data from your web server and perform server-side validation. HTML5 – This is how you implement client-side validation. Sammy – This is how you implement client-side routing and create a Single Page App with multiple virtual pages. There are code samples in the download (look in the Samples folder) which demonstrate how all of these technologies work when building Single Page Apps. Powerpoint Sample Code

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  • Apache redirecting: reason unknown

    - by Sinan
    I have a simple php script. The script is not important. It just prints out $_SERVER. When I request an URL like www.server.com/?ref=bar everything is fine. However if the request contains something like www.server.com/?ref=http://www.test.com (?ref=http%3A%2F%2Fwww.test.com) the server redirects to 403.shtml. No redirect for http://x but redirects http://x.y As far as I can understand somehow the server doesn't like "http://x". It always redirects to 403.shtml when there is a valid query string in the form of a valid url. my .htacess file is the same both on my server and local test server and local test server behaves as expected (no redirects). So I don't it is related to .htaccess. I'm on shared host on Hostgator. Can anyone help? Edit: Here's the .htaccess file Options +FollowSymLinks RewriteEngine On RewriteBase / RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteRule ^(.*)$ index.php?$1 [L,QSA] When there is an http://xx.x it redirects to 403 even if there is physical file. However if I remove the .htaccess redirect to 403 also disappears. But I need the above .htaccess file. Is there a way to get around this?

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  • Database Replication check script not running

    - by Tarun
    I'm trying to create a Database Replication checking script but I'm getting error while executing it. Here is the script #!/bin/bash PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin export PATH #Server Name Server="Test Server" #My Sql Username and Password User=root Password="a" #Maximum Slave Time Delay Delay="60" #File Path to store error and email the same Log_File=/tmp/replicationcheck.txt #Email Settings Subject="$Server Replication Error" Sender_Name=TestServer Recipients="[email protected]" #Mail Alert Function mailalert(){ sendmail -F $Sender_Name -it <<END_MESSAGE To: $Recipients Subject: $Subject $Message_Replication_Error `/bin/cat $Log_File` END_MESSAGE } #Show Slave Status Show_Slave_Status=`echo "show slave status \G;" | mysql -u $User -p$Password 2>&1` #Getting list of queries in mysql $Show_Slave_Status | grep "Last_" > $Log_File #Check if slave running $Show_Slave_Status | grep "Slave_IO_Running: No" if [ "$?" -eq "0" ]; then Message_Replication_Error="$Server Replication error please check. The Slave_IO_Running state is No." mailalert exit 1 else $Show_Slave_Status | grep "Slave_IO_Running: Connecting" if [ "$?" -eq "0" ]; then Message_Replication_Error="$Server Replication error please check. The Slave_IO_Running state is Connecting." mailalert exit 1 fi fi #Check if replication delayed Seconds_Behind_Master=$Show_Slave_Status | grep "Seconds_Behind_Master" | awk -F": " {' print $2 '} if [ "$Seconds_Behind_Master" -ge "$Delay" ]; then Message_Replication_Error="Replication Delayed by $Seconds_Behind_Master." mailalert else if [ "$Seconds_Behind_Master" = "NULL" ]; then Message_Replication_Error="$Server Replication error please check. The Seconds_Behind_Master state is NULL." mailalert fi fi

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  • How to implement lockstep model for RTS game?

    - by user11177
    In my effort to learn programming I'm trying to make a small RTS style game. I've googled and read a lot of articles and gamedev q&a's on the topic of lockstep synchronization in multiplayer RTS games, but am still having trouble wrapping my head around how to implement it in my own game. I currently have a simple server/client system. For example if player1 selects a unit and gives the command to move it, the client sends the command [move, unit, coordinates] to the server, the server runs the pathfinding function and sends [move, unit, path] to all clients which then moves the unit and run animations. So far so good, but not synchronized for clients with latency or lower/higher FPS. How can I turn this into a true lockstep system? Is the right methodology supposed to be something like the following, using the example from above: Turn 1 start gather command inputs from player1 send to the server turn number and commands end turn, increment turn number The server receives the commands, runs pathfinding and sends the paths to all clients. Next turn receive paths from server, as well as confirmation that all clients completed previous turn, otherwise pause and wait for that confirmation move units gather new inputs end turn Is that the gist of it? Should perhaps pathfinding and other game logic be done client side instead of on the server, if so why? Is there anything else I'm missing? I hope someone can break down the concept, so I understand it better.

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  • Solution for installing the ADF 11.1.1.6.0 Runtimes onto a standalone WLS 10.3.6

    - by Chris Muir
    A few customers are hitting the following problem with regards to JDeveloper 11.1.1.6.0 so it's worth documenting a solution. As noted in my previous post the ADF Runtimes for JDeveloper 11.1.1.6.0 will work against a 10.3.5 and 10.3.6 WLS server.  In terms of the JDeveloper 11.1.1.6.0 download Oracle has coupled the 10.3.5 server with that release, not a 10.3.6 server. This has caught some customers out as they are attempting to use the JDeveloper installer to load the 11.1.1.6.0 ADF Runtimes into the middleware home of a standalone 10.3.6 WLS server.  When doing so the installer complains as follows: "The product maintenance level of the current server (WebLogic Server: 10.3.5.0) is not compatible with the maintenance level of the product installed on your system (WebLogic Server: 10.3.6.0).  Please obtain a compatible installer or perform maintenance or your current system to achieve the desired level." The solution is to install the runtimes using the standalone 11.1.1.6.0 ADF Runtime Libraries installer available from OTN (see the options under "Application Development Runtime").

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  • Packages not showing up in created APT repository

    - by David
    I created an APT repository using deb-scanpackages, and it seemed to go well. When I did a apt-get update on another server, the Packages.gz file was retrieved, and all seemed well - until I went to search for the packages contained in that repository (all packages are created locally). Several recommendations suggested reprepro; I tried that. Same result - except I had to rebuild the packages with the Priority and Section lines in the control file (nothing says this anywhere). The reprepro utility also generates a complicated directory structure which required rewriting the repository entry on the requesting server. I then found that the arch directory referenced i386 and not amd64 (which was requested by the requesting server). Is it possible that the AMD64 system isn't seeing packages compiled for i386? Searching the *Packages files in /var/lib/apt/lists show that the only packages for i386 are those I added (the other files are for the server - Ubuntu 10.04.2 LTS). The server the packages were built on is Ubuntu 10.04.2 LTS i686; the requesting server is x86_64. I found some discussion at the Debian AMD64FAQ but it claims to be obsolete. It makes mention of an extended syntax for repository listings for APT, and a command dpkg-subarchitecture - neither of which work on the local AMD64 server. Do I have to build two different sets of packages?

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  • Fun with Aggregates

    - by Paul White
    There are interesting things to be learned from even the simplest queries.  For example, imagine you are given the task of writing a query to list AdventureWorks product names where the product has at least one entry in the transaction history table, but fewer than ten. One possible query to meet that specification is: SELECT p.Name FROM Production.Product AS p JOIN Production.TransactionHistory AS th ON p.ProductID = th.ProductID GROUP BY p.ProductID, p.Name HAVING COUNT_BIG(*) < 10; That query correctly returns 23 rows (execution plan and data sample shown below): The execution plan looks a bit different from the written form of the query: the base tables are accessed in reverse order, and the aggregation is performed before the join.  The general idea is to read all rows from the history table, compute the count of rows grouped by ProductID, merge join the results to the Product table on ProductID, and finally filter to only return rows where the count is less than ten. This ‘fully-optimized’ plan has an estimated cost of around 0.33 units.  The reason for the quote marks there is that this plan is not quite as optimal as it could be – surely it would make sense to push the Filter down past the join too?  To answer that, let’s look at some other ways to formulate this query.  This being SQL, there are any number of ways to write logically-equivalent query specifications, so we’ll just look at a couple of interesting ones.  The first query is an attempt to reverse-engineer T-SQL from the optimized query plan shown above.  It joins the result of pre-aggregating the history table to the Product table before filtering: SELECT p.Name FROM ( SELECT th.ProductID, cnt = COUNT_BIG(*) FROM Production.TransactionHistory AS th GROUP BY th.ProductID ) AS q1 JOIN Production.Product AS p ON p.ProductID = q1.ProductID WHERE q1.cnt < 10; Perhaps a little surprisingly, we get a slightly different execution plan: The results are the same (23 rows) but this time the Filter is pushed below the join!  The optimizer chooses nested loops for the join, because the cardinality estimate for rows passing the Filter is a bit low (estimate 1 versus 23 actual), though you can force a merge join with a hint and the Filter still appears below the join.  In yet another variation, the < 10 predicate can be ‘manually pushed’ by specifying it in a HAVING clause in the “q1” sub-query instead of in the WHERE clause as written above. The reason this predicate can be pushed past the join in this query form, but not in the original formulation is simply an optimizer limitation – it does make efforts (primarily during the simplification phase) to encourage logically-equivalent query specifications to produce the same execution plan, but the implementation is not completely comprehensive. Moving on to a second example, the following query specification results from phrasing the requirement as “list the products where there exists fewer than ten correlated rows in the history table”: SELECT p.Name FROM Production.Product AS p WHERE EXISTS ( SELECT * FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID HAVING COUNT_BIG(*) < 10 ); Unfortunately, this query produces an incorrect result (86 rows): The problem is that it lists products with no history rows, though the reasons are interesting.  The COUNT_BIG(*) in the EXISTS clause is a scalar aggregate (meaning there is no GROUP BY clause) and scalar aggregates always produce a value, even when the input is an empty set.  In the case of the COUNT aggregate, the result of aggregating the empty set is zero (the other standard aggregates produce a NULL).  To make the point really clear, let’s look at product 709, which happens to be one for which no history rows exist: -- Scalar aggregate SELECT COUNT_BIG(*) FROM Production.TransactionHistory AS th WHERE th.ProductID = 709;   -- Vector aggregate SELECT COUNT_BIG(*) FROM Production.TransactionHistory AS th WHERE th.ProductID = 709 GROUP BY th.ProductID; The estimated execution plans for these two statements are almost identical: You might expect the Stream Aggregate to have a Group By for the second statement, but this is not the case.  The query includes an equality comparison to a constant value (709), so all qualified rows are guaranteed to have the same value for ProductID and the Group By is optimized away. In fact there are some minor differences between the two plans (the first is auto-parameterized and qualifies for trivial plan, whereas the second is not auto-parameterized and requires cost-based optimization), but there is nothing to indicate that one is a scalar aggregate and the other is a vector aggregate.  This is something I would like to see exposed in show plan so I suggested it on Connect.  Anyway, the results of running the two queries show the difference at runtime: The scalar aggregate (no GROUP BY) returns a result of zero, whereas the vector aggregate (with a GROUP BY clause) returns nothing at all.  Returning to our EXISTS query, we could ‘fix’ it by changing the HAVING clause to reject rows where the scalar aggregate returns zero: SELECT p.Name FROM Production.Product AS p WHERE EXISTS ( SELECT * FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID HAVING COUNT_BIG(*) BETWEEN 1 AND 9 ); The query now returns the correct 23 rows: Unfortunately, the execution plan is less efficient now – it has an estimated cost of 0.78 compared to 0.33 for the earlier plans.  Let’s try adding a redundant GROUP BY instead of changing the HAVING clause: SELECT p.Name FROM Production.Product AS p WHERE EXISTS ( SELECT * FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY th.ProductID HAVING COUNT_BIG(*) < 10 ); Not only do we now get correct results (23 rows), this is the execution plan: I like to compare that plan to quantum physics: if you don’t find it shocking, you haven’t understood it properly :)  The simple addition of a redundant GROUP BY has resulted in the EXISTS form of the query being transformed into exactly the same optimal plan we found earlier.  What’s more, in SQL Server 2008 and later, we can replace the odd-looking GROUP BY with an explicit GROUP BY on the empty set: SELECT p.Name FROM Production.Product AS p WHERE EXISTS ( SELECT * FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY () HAVING COUNT_BIG(*) < 10 ); I offer that as an alternative because some people find it more intuitive (and it perhaps has more geek value too).  Whichever way you prefer, it’s rather satisfying to note that the result of the sub-query does not exist for a particular correlated value where a vector aggregate is used (the scalar COUNT aggregate always returns a value, even if zero, so it always ‘EXISTS’ regardless which ProductID is logically being evaluated). The following query forms also produce the optimal plan and correct results, so long as a vector aggregate is used (you can probably find more equivalent query forms): WHERE Clause SELECT p.Name FROM Production.Product AS p WHERE ( SELECT COUNT_BIG(*) FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY () ) < 10; APPLY SELECT p.Name FROM Production.Product AS p CROSS APPLY ( SELECT NULL FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY () HAVING COUNT_BIG(*) < 10 ) AS ca (dummy); FROM Clause SELECT q1.Name FROM ( SELECT p.Name, cnt = ( SELECT COUNT_BIG(*) FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY () ) FROM Production.Product AS p ) AS q1 WHERE q1.cnt < 10; This last example uses SUM(1) instead of COUNT and does not require a vector aggregate…you should be able to work out why :) SELECT q.Name FROM ( SELECT p.Name, cnt = ( SELECT SUM(1) FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID ) FROM Production.Product AS p ) AS q WHERE q.cnt < 10; The semantics of SQL aggregates are rather odd in places.  It definitely pays to get to know the rules, and to be careful to check whether your queries are using scalar or vector aggregates.  As we have seen, query plans do not show in which ‘mode’ an aggregate is running and getting it wrong can cause poor performance, wrong results, or both. © 2012 Paul White Twitter: @SQL_Kiwi email: [email protected]

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  • Why is Ubuntu's clock getting slower or faster?

    - by ændrük
    Ubuntu's clock is off by about a half hour: Where do I even start troubleshooting this? It's allegedly being set "automatically from the Internet". How can I verify that "the Internet" knows what time it is? Details Ubuntu has had plenty of time to communicate with the Internet: $ date; uptime Fri May 18 05:56:00 PDT 2012 05:56:00 up 12 days, 10:48, 2 users, load average: 0.61, 0.96, 1.15 This time server I found via a web search does appear to know the correct time: $ date; ntpdate -q north-america.pool.ntp.org Fri May 18 05:56:09 PDT 2012 server 208.38.65.37, stratum 2, offset 1752.625337, delay 0.10558 server 46.166.138.172, stratum 2, offset 1752.648597, delay 0.10629 server 205.189.158.228, stratum 3, offset 1752.672466, delay 0.11829 18 May 05:56:18 ntpdate[29752]: step time server 208.38.65.37 offset 1752.625337 sec There aren't any reported errors related to NTP: $ grep -ic ntp /var/log/syslog 0 After rebooting, the time was automatically corrected and the following appeared in /var/log/syslog: May 18 17:58:12 aux ntpdate[1891]: step time server 91.189.94.4 offset 1838.497277 sec A log of the offset reported by ntpdate reveals that the clock is drifting by about 9 seconds every hour: $ while true; do ntpdate-debian -q | tail -n 1 >> 'drift.log'; sleep 16m; done ^C $ r -e ' attach(read.table("drift.log", header=FALSE)) clock <- as.POSIXct(paste(V1, V2, V3), format="%d %b %H:%M:%S") fit <- lm(V10~clock) png("drift.png") plot(clock, V10, xlab="Clock time", ylab="Time server offset (s)") abline(fit) mtext(sprintf("Drift rate: %.2f s/hr", fit$coefficients[[2]]*3600)) '

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  • Choosing Technology To Include In Software Design

    How many of us have been forced to select one technology over another when designing a new system? What factors do we and should we consider? How can we ensure the correct business decision is made? When faced with this type of decision it is important to gather as much information possible regarding each technology being considered as well as the project itself. Additionally, I tend to delay my decision about the technology until it is ultimately necessary to be made. The reason why I tend to delay such an important design decision is due to the fact that as the project progresses requirements and other factors can alter a decision for selecting the best technology for a project. Important factors to consider when making technology decisions: Time to Implement and Maintain Total Cost of Technology (including Implementation and maintenance) Adaptability of Technology Implementation Team’s Skill Sets Complexity of Technology (including Implementation and maintenance) orecasted Return On Investment (ROI) Forecasted Profit on Investment (POI) Of the factors to consider the ROI and POI weigh the heaviest because the take in to consideration the other factors when calculating the profitability and return on investments.For a real world example let us consider developing a web based lead management system for a new company. This system can either be hosted on Microsoft Windows based web server or on a Linux based web server. Important Factors for this Example Implementation Team’s Skill Sets Member 1  Skill Set: Classic ASP, ASP.Net, and MS SQL Server Experience: 10 years Member 2  Skill Set: PHP, MySQL, Photoshop and MS SQL Server Experience: 3 years Member 3  Skill Set: C++, VB6, ASP.Net, and MS SQL Server Experience: 12 years Total Cost of Technology (including Implementation and maintenance) Linux Initial Year: $5,000 (Random Value) Additional Years: $3,000 (Random Value) Windows Initial Year: $10,000 (Random Value) Additional Years: $3,000 (Random Value) Complexity of Technology Linux Large Learning Curve with user driven documentation Estimated learning cost: $30,000 Windows Minimal based on Teams skills with Microsoft based documentation Estimated learning cost: $5,000 ROI Linux Total Cost Initial Total Cost: $35,000 Additional Cost $3,000 per year Windows Total Cost Initial Total Cost: $15,000 Additional Cost $3,000 per year Based on the hypothetical numbers it would make more sense to select windows based web server because the initial investment of the technology is much lower initially compared to the Linux based web server.

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  • "Can't open display" even after access with xhost

    - by Yann
    I'm trying to run a graphical program remotely, without using ssh. I've set the display variable on the server (let's say server.com, Linux, not ubuntu, and no su rights) to point to my workstation (workstation.com, ubuntu 10.04) setenv DISPLAY workstation.com:0 Then on my workstation I've tried both xhost +server.com and xhost + Then I ssh into the server (to test things): ssh [email protected] and try to run xclock, and get the following error: Error: Can't open display: workstation.com:0 I've looked at /etc/ssh/ssh_config on the workstation and I should be forwarding correctly: X11Forwarding yes. How do I go about troubleshooting this? What logs on the workstation document these failed attempts? To explain why I'm doing this: I want to run a batch job on a server to debug an MPI-based parallel program. I want to run xterm as the batch job executable, per the instructions provided by the system admins. This setup use to work. I reinstalled things on my workstation and since then I frequently get one-time message along the lines The authenticity of host 'hostname (XXX.XXX.XXX.XX)' can't be established. My attempt to fix the above was to move my ~/.ssh/known_hosts file to a back up on both server and host, and then to ssh from each to the other with the flag -o StrictHostKeyChecking=no. I no longer get that message, but I was wondering does this play a part in why X11 forwarding is not working?

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