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  • SQL SERVER – BACKUPIO, BACKUPBUFFER – Wait Type – Day 14 of 28

    - by pinaldave
    Backup is the most important task for any database admin. Your data is at risk if you are not performing database backup. Honestly, I have seen many DBAs who know how to take backups but do not know how to restore it. (Sigh!) In this blog post we are going to discuss about one of my real experiences with one of my clients – BACKUPIO. When I started to deal with it, I really had no idea how to fix the issue. However, after fixing it at two places, I think I know why this is happening but at the same time, I am not sure the fix is the best solution. The reality is that the fix is not a solution but a workaround (which is not optimal, but get your things done). From Book On-Line: BACKUPIO Occurs when a backup task is waiting for data, or is waiting for a buffer in which to store data. This type is not typical, except when a task is waiting for a tape mount. BACKUPBUFFER Occurs when a backup task is waiting for data, or is waiting for a buffer in which to store data. This type is not typical, except when a task is waiting for a tape mount. BACKUPIO and BACKUPBUFFER Explanation: This wait stats will occur when you are taking the backup on the tape or any other extremely slow backup system. Reducing BACKUPIO and BACKUPBUFFER wait: In my recent consultancy, backup on tape was very slow probably because the tape system was very old. During the time when I explained this wait type reason in the consultancy, the owners immediately decided to replace the tape drive with an alternate system. They had a small SAN enclosure not being used on side, which they decided to re-purpose. After a week, I had received an email from their DBA, saying that the wait stats have reduced drastically. At another location, my client was using a third party tool (please don’t ask me the name of the tool) to take backup. This tool was compressing the backup along with taking backup. I have had a very good experience with this tool almost all the time except this one sparse experience. When I tried to take backup using the native SQL Server compressed backup, there was a very small value on this wait type and the backup was much faster. However, when I attempted with the third party backup tool, this value was very high again and was taking much more time. The third party tool had many other features but the client was not using these features. We end up using the native SQL Server Compressed backup and it worked very well. If I get to see this higher in my future consultancy, I will try to understand this wait type much more in detail and so probably I would able to come to some solid solution. Read all the post in the Wait Types and Queue series. Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All the discussion of Wait Stats in this blog is generic and varies from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQL SERVER – ASYNC_IO_COMPLETION – Wait Type – Day 11 of 28

    - by pinaldave
    For any good system three things are vital: CPU, Memory and IO (disk). Among these three, IO is the most crucial factor of SQL Server. Looking at real-world cases, I do not see IT people upgrading CPU and Memory frequently. However, the disk is often upgraded for either improving the space, speed or throughput. Today we will look at another IO-related wait type. From Book On-Line: Occurs when a task is waiting for I/Os to finish. ASYNC_IO_COMPLETION Explanation: Any tasks are waiting for I/O to finish. If by any means your application that’s connected to SQL Server is processing the data very slowly, this type of wait can occur. Several long-running database operations like BACKUP, CREATE DATABASE, ALTER DATABASE or other operations can also create this wait type. Reducing ASYNC_IO_COMPLETION wait: When it is an issue related to IO, one should check for the following things associated to IO subsystem: Look at the programming and see if there is any application code which processes the data slowly (like inefficient loop, etc.). Note that it should be re-written to avoid this  wait type. Proper placing of the files is very important. We should check the file system for proper placement of the files – LDF and MDF on separate drive, TempDB on another separate drive, hot spot tables on separate filegroup (and on separate disk), etc. Check the File Statistics and see if there is a higher IO Read and IO Write Stall SQL SERVER – Get File Statistics Using fn_virtualfilestats. Check event log and error log for any errors or warnings related to IO. If you are using SAN (Storage Area Network), check the throughput of the SAN system as well as configuration of the HBA Queue Depth. In one of my recent projects, the SAN was performing really badly and so the SAN administrator did not accept it. After some investigations, he agreed to change the HBA Queue Depth on the development setup (test environment). As soon as we changed the HBA Queue Depth to quite a higher value, there was a sudden big improvement in the performance. It is very likely to happen that there are no proper indexes on the system and yet there are lots of table scans and heap scans. Creating proper index can reduce the IO bandwidth considerably. If SQL Server can use appropriate cover index instead of clustered index, it can effectively reduce lots of CPU, Memory and IO (considering cover index has lesser columns than cluster table and all other; it depends upon the situation). You can refer to the following two articles I wrote that talk about how to optimize indexes: Create Missing Indexes Drop Unused Indexes Checking Memory Related Perfmon Counters SQLServer: Memory Manager\Memory Grants Pending (Consistent higher value than 0-2) SQLServer: Memory Manager\Memory Grants Outstanding (Consistent higher value, Benchmark) SQLServer: Buffer Manager\Buffer Hit Cache Ratio (Higher is better, greater than 90% for usually smooth running system) SQLServer: Buffer Manager\Page Life Expectancy (Consistent lower value than 300 seconds) Memory: Available Mbytes (Information only) Memory: Page Faults/sec (Benchmark only) Memory: Pages/sec (Benchmark only) Checking Disk Related Perfmon Counters Average Disk sec/Read (Consistent higher value than 4-8 millisecond is not good) Average Disk sec/Write (Consistent higher value than 4-8 millisecond is not good) Average Disk Read/Write Queue Length (Consistent higher value than benchmark is not good) Read all the post in the Wait Types and Queue series. Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All the discussions of Wait Stats in this blog are generic and vary from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQL SERVER – PAGEIOLATCH_DT, PAGEIOLATCH_EX, PAGEIOLATCH_KP, PAGEIOLATCH_SH, PAGEIOLATCH_UP – Wait Type – Day 9 of 28

    - by pinaldave
    It is very easy to say that you replace your hardware as that is not up to the mark. In reality, it is very difficult to implement. It is really hard to convince an infrastructure team to change any hardware because they are not performing at their best. I had a nightmare related to this issue in a deal with an infrastructure team as I suggested that they replace their faulty hardware. This is because they were initially not accepting the fact that it is the fault of their hardware. But it is really easy to say “Trust me, I am correct”, while it is equally important that you put some logical reasoning along with this statement. PAGEIOLATCH_XX is such a kind of those wait stats that we would directly like to blame on the underlying subsystem. Of course, most of the time, it is correct – the underlying subsystem is usually the problem. From Book On-Line: PAGEIOLATCH_DT Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Destroy mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_EX Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Exclusive mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_KP Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Keep mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_SH Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Shared mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_UP Occurs when a task is waiting on a latch for a buffer that is in an I/O request. The latch request is in Update mode. Long waits may indicate problems with the disk subsystem. PAGEIOLATCH_XX Explanation: Simply put, this particular wait type occurs when any of the tasks is waiting for data from the disk to move to the buffer cache. ReducingPAGEIOLATCH_XX wait: Just like any other wait type, this is again a very challenging and interesting subject to resolve. Here are a few things you can experiment on: Improve your IO subsystem speed (read the first paragraph of this article, if you have not read it, I repeat that it is easy to say a step like this than to actually implement or do it). This type of wait stats can also happen due to memory pressure or any other memory issues. Putting aside the issue of a faulty IO subsystem, this wait type warrants proper analysis of the memory counters. If due to any reasons, the memory is not optimal and unable to receive the IO data. This situation can create this kind of wait type. Proper placing of files is very important. We should check file system for the proper placement of files – LDF and MDF on separate drive, TempDB on separate drive, hot spot tables on separate filegroup (and on separate disk), etc. Check the File Statistics and see if there is higher IO Read and IO Write Stall SQL SERVER – Get File Statistics Using fn_virtualfilestats. It is very possible that there are no proper indexes on the system and there are lots of table scans and heap scans. Creating proper index can reduce the IO bandwidth considerably. If SQL Server can use appropriate cover index instead of clustered index, it can significantly reduce lots of CPU, Memory and IO (considering cover index has much lesser columns than cluster table and all other it depends conditions). You can refer to the two articles’ links below previously written by me that talk about how to optimize indexes. Create Missing Indexes Drop Unused Indexes Updating statistics can help the Query Optimizer to render optimal plan, which can only be either directly or indirectly. I have seen that updating statistics with full scan (again, if your database is huge and you cannot do this – never mind!) can provide optimal information to SQL Server optimizer leading to efficient plan. Checking Memory Related Perfmon Counters SQLServer: Memory Manager\Memory Grants Pending (Consistent higher value than 0-2) SQLServer: Memory Manager\Memory Grants Outstanding (Consistent higher value, Benchmark) SQLServer: Buffer Manager\Buffer Hit Cache Ratio (Higher is better, greater than 90% for usually smooth running system) SQLServer: Buffer Manager\Page Life Expectancy (Consistent lower value than 300 seconds) Memory: Available Mbytes (Information only) Memory: Page Faults/sec (Benchmark only) Memory: Pages/sec (Benchmark only) Checking Disk Related Perfmon Counters Average Disk sec/Read (Consistent higher value than 4-8 millisecond is not good) Average Disk sec/Write (Consistent higher value than 4-8 millisecond is not good) Average Disk Read/Write Queue Length (Consistent higher value than benchmark is not good) Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All of the discussions of Wait Stats in this blog is generic and varies from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQL SERVER – DMV – sys.dm_os_waiting_tasks and sys.dm_exec_requests – Wait Type – Day 4 of 28

    - by pinaldave
    Previously, we covered the DMV sys.dm_os_wait_stats, and also saw how it can be useful to identify the major resource bottleneck. However, at the same time, we discussed that this is only useful when we are looking at an instance-level picture. Quite often we want to know about the processes going in our server at the given instant. Here is the query for the same. This DMV is written taking the following into consideration: we want to analyze the queries that are currently running or which have recently ran and their plan is still in the cache. SELECT dm_ws.wait_duration_ms, dm_ws.wait_type, dm_es.status, dm_t.TEXT, dm_qp.query_plan, dm_ws.session_ID, dm_es.cpu_time, dm_es.memory_usage, dm_es.logical_reads, dm_es.total_elapsed_time, dm_es.program_name, DB_NAME(dm_r.database_id) DatabaseName, -- Optional columns dm_ws.blocking_session_id, dm_r.wait_resource, dm_es.login_name, dm_r.command, dm_r.last_wait_type FROM sys.dm_os_waiting_tasks dm_ws INNER JOIN sys.dm_exec_requests dm_r ON dm_ws.session_id = dm_r.session_id INNER JOIN sys.dm_exec_sessions dm_es ON dm_es.session_id = dm_r.session_id CROSS APPLY sys.dm_exec_sql_text (dm_r.sql_handle) dm_t CROSS APPLY sys.dm_exec_query_plan (dm_r.plan_handle) dm_qp WHERE dm_es.is_user_process = 1 GO You can change CROSS APPLY to OUTER APPLY if you want to see all the details which are omitted because of the plan cache. Let us analyze the result of the above query and see how it can be helpful to identify the query and the kind of wait type it creates. Click to Enlarage The above query will return various columns. There are various columns that provide very important details. e.g. wait_duration_ms – it indicates current wait for the query that executes at that point of time. wait_type – it indicates the current wait type for the query text – indicates the query text query_plan – when clicked on the same, it will display the query plans There are many other important information like CPU_time, memory_usage, and logical_reads, which can be read from the query as well. In future posts on this series, we will see how once identified wait type we can attempt to reduce the same. Read all the post in the Wait Types and Queue series. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: DMV, Pinal Dave, PostADay, SQL, SQL Authority, SQL DMV, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • C-states and P-states : confounding factors for benchmarking

    - by Dave
    I was recently looking into a performance issue in the java.util.concurrent (JUC) fork-join pool framework related to particularly long latencies when trying to wake (unpark) threads in the pool. Eventually I tracked the issue down to the power & scaling governor and idle-state policies on x86. Briefly, P-states refer to the set of clock rates (speeds) at which a processor can run. C-states reflect the possible idle states. The deeper the C-state (higher numerical values) the less power the processor will draw, but the longer it takes the processor to respond and exit that sleep state on the next idle to non-idle transition. In some cases the latency can be worse than 100 microseconds. C0 is normal execution state, and P0 is "full speed" with higher Pn values reflecting reduced clock rates. C-states are P-states are orthogonal, although P-states only have meaning at C0. You could also think of the states as occupying a spectrum as follows : P0, P1, P2, Pn, C1, C2, ... Cn, where all the P-states are at C0. Our fork-join framework was calling unpark() to wake a thread from the pool, and that thread was being dispatched onto a processor at deep C-state, so we were observing rather impressive latencies between the time of the unpark and the time the thread actually resumed and was able to accept work. (I originally thought we were seeing situations where the wakee was preempting the waker, but that wasn't the case. I'll save that topic for a future blog entry). It's also worth pointing out that higher P-state values draw less power and there's usually some latency in ramping up the clock (P-states) in response to offered load. The issue of C-states and P-states isn't new and has been described at length elsewhere, but it may be new to Java programmers, adding a new confounding factor to benchmarking methodologies and procedures. To get stable results I'd recommend running at C0 and P0, particularly for server-side applications. As appropriate, disabling "turbo" mode may also be prudent. But it also makes sense to run with the system defaults to understand if your application exhibits any performance sensitivity to power management policies. The operating system power management sub-system typically control the P-state and C-states based on current and recent load. The scaling governor manages P-states. Operating systems often use adaptive policies that try to avoid deep C-states for some period if recent deep idle episodes proved to be very short and futile. This helps make the system more responsive under bursty or otherwise irregular load. But it also means the system is stateful and exhibits a memory effect, which can further complicate benchmarking. Forcing C0 + P0 should avoid this issue.

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  • SQL SERVER – Guest Post – Jonathan Kehayias – Wait Type – Day 16 of 28

    - by pinaldave
    Jonathan Kehayias (Blog | Twitter) is a MCITP Database Administrator and Developer, who got started in SQL Server in 2004 as a database developer and report writer in the natural gas industry. After spending two and a half years working in TSQL, in late 2006, he transitioned to the role of SQL Database Administrator. His primary passion is performance tuning, where he frequently rewrites queries for better performance and performs in depth analysis of index implementation and usage. Jonathan blogs regularly on SQLBlog, and was a coauthor of Professional SQL Server 2008 Internals and Troubleshooting. On a personal note, I think Jonathan is extremely positive person. In every conversation with him I have found that he is always eager to help and encourage. Every time he finds something needs to be approved, he has contacted me without hesitation and guided me to improve, change and learn. During all the time, he has not lost his focus to help larger community. I am honored that he has accepted to provide his views on complex subject of Wait Types and Queues. Currently I am reading his series on Extended Events. Here is the guest blog post by Jonathan: SQL Server troubleshooting is all about correlating related pieces of information together to indentify where exactly the root cause of a problem lies. In my daily work as a DBA, I generally get phone calls like, “So and so application is slow, what’s wrong with the SQL Server.” One of the funny things about the letters DBA is that they go so well with Default Blame Acceptor, and I really wish that I knew exactly who the first person was that pointed that out to me, because it really fits at times. A lot of times when I get this call, the problem isn’t related to SQL Server at all, but every now and then in my initial quick checks, something pops up that makes me start looking at things further. The SQL Server is slow, we see a number of tasks waiting on ASYNC_IO_COMPLETION, IO_COMPLETION, or PAGEIOLATCH_* waits in sys.dm_exec_requests and sys.dm_exec_waiting_tasks. These are also some of the highest wait types in sys.dm_os_wait_stats for the server, so it would appear that we have a disk I/O bottleneck on the machine. A quick check of sys.dm_io_virtual_file_stats() and tempdb shows a high write stall rate, while our user databases show high read stall rates on the data files. A quick check of some performance counters and Page Life Expectancy on the server is bouncing up and down in the 50-150 range, the Free Page counter consistently hits zero, and the Free List Stalls/sec counter keeps jumping over 10, but Buffer Cache Hit Ratio is 98-99%. Where exactly is the problem? In this case, which happens to be based on a real scenario I faced a few years back, the problem may not be a disk bottleneck at all; it may very well be a memory pressure issue on the server. A quick check of the system spec’s and it is a dual duo core server with 8GB RAM running SQL Server 2005 SP1 x64 on Windows Server 2003 R2 x64. Max Server memory is configured at 6GB and we think that this should be enough to handle the workload; or is it? This is a unique scenario because there are a couple of things happening inside of this system, and they all relate to what the root cause of the performance problem is on the system. If we were to query sys.dm_exec_query_stats for the TOP 10 queries, by max_physical_reads, max_logical_reads, and max_worker_time, we may be able to find some queries that were using excessive I/O and possibly CPU against the system in their worst single execution. We can also CROSS APPLY to sys.dm_exec_sql_text() and see the statement text, and also CROSS APPLY sys.dm_exec_query_plan() to get the execution plan stored in cache. Ok, quick check, the plans are pretty big, I see some large index seeks, that estimate 2.8GB of data movement between operators, but everything looks like it is optimized the best it can be. Nothing really stands out in the code, and the indexing looks correct, and I should have enough memory to handle this in cache, so it must be a disk I/O problem right? Not exactly! If we were to look at how much memory the plan cache is taking by querying sys.dm_os_memory_clerks for the CACHESTORE_SQLCP and CACHESTORE_OBJCP clerks we might be surprised at what we find. In SQL Server 2005 RTM and SP1, the plan cache was allowed to take up to 75% of the memory under 8GB. I’ll give you a second to go back and read that again. Yes, you read it correctly, it says 75% of the memory under 8GB, but you don’t have to take my word for it, you can validate this by reading Changes in Caching Behavior between SQL Server 2000, SQL Server 2005 RTM and SQL Server 2005 SP2. In this scenario the application uses an entirely adhoc workload against SQL Server and this leads to plan cache bloat, and up to 4.5GB of our 6GB of memory for SQL can be consumed by the plan cache in SQL Server 2005 SP1. This in turn reduces the size of the buffer cache to just 1.5GB, causing our 2.8GB of data movement in this expensive plan to cause complete flushing of the buffer cache, not just once initially, but then another time during the queries execution, resulting in excessive physical I/O from disk. Keep in mind that this is not the only query executing at the time this occurs. Remember the output of sys.dm_io_virtual_file_stats() showed high read stalls on the data files for our user databases versus higher write stalls for tempdb? The memory pressure is also forcing heavier use of tempdb to handle sorting and hashing in the environment as well. The real clue here is the Memory counters for the instance; Page Life Expectancy, Free List Pages, and Free List Stalls/sec. The fact that Page Life Expectancy is fluctuating between 50 and 150 constantly is a sign that the buffer cache is experiencing constant churn of data, once every minute to two and a half minutes. If you add to the Page Life Expectancy counter, the consistent bottoming out of Free List Pages along with Free List Stalls/sec consistently spiking over 10, and you have the perfect memory pressure scenario. All of sudden it may not be that our disk subsystem is the problem, but is instead an innocent bystander and victim. Side Note: The Page Life Expectancy counter dropping briefly and then returning to normal operating values intermittently is not necessarily a sign that the server is under memory pressure. The Books Online and a number of other references will tell you that this counter should remain on average above 300 which is the time in seconds a page will remain in cache before being flushed or aged out. This number, which equates to just five minutes, is incredibly low for modern systems and most published documents pre-date the predominance of 64 bit computing and easy availability to larger amounts of memory in SQL Servers. As food for thought, consider that my personal laptop has more memory in it than most SQL Servers did at the time those numbers were posted. I would argue that today, a system churning the buffer cache every five minutes is in need of some serious tuning or a hardware upgrade. Back to our problem and its investigation: There are two things really wrong with this server; first the plan cache is excessively consuming memory and bloated in size and we need to look at that and second we need to evaluate upgrading the memory to accommodate the workload being performed. In the case of the server I was working on there were a lot of single use plans found in sys.dm_exec_cached_plans (where usecounts=1). Single use plans waste space in the plan cache, especially when they are adhoc plans for statements that had concatenated filter criteria that is not likely to reoccur with any frequency.  SQL Server 2005 doesn’t natively have a way to evict a single plan from cache like SQL Server 2008 does, but MVP Kalen Delaney, showed a hack to evict a single plan by creating a plan guide for the statement and then dropping that plan guide in her blog post Geek City: Clearing a Single Plan from Cache. We could put that hack in place in a job to automate cleaning out all the single use plans periodically, minimizing the size of the plan cache, but a better solution would be to fix the application so that it uses proper parameterized calls to the database. You didn’t write the app, and you can’t change its design? Ok, well you could try to force parameterization to occur by creating and keeping plan guides in place, or we can try forcing parameterization at the database level by using ALTER DATABASE <dbname> SET PARAMETERIZATION FORCED and that might help. If neither of these help, we could periodically dump the plan cache for that database, as discussed as being a problem in Kalen’s blog post referenced above; not an ideal scenario. The other option is to increase the memory on the server to 16GB or 32GB, if the hardware allows it, which will increase the size of the plan cache as well as the buffer cache. In SQL Server 2005 SP1, on a system with 16GB of memory, if we set max server memory to 14GB the plan cache could use at most 9GB  [(8GB*.75)+(6GB*.5)=(6+3)=9GB], leaving 5GB for the buffer cache.  If we went to 32GB of memory and set max server memory to 28GB, the plan cache could use at most 16GB [(8*.75)+(20*.5)=(6+10)=16GB], leaving 12GB for the buffer cache. Thankfully we have SQL Server 2005 Service Pack 2, 3, and 4 these days which include the changes in plan cache sizing discussed in the Changes to Caching Behavior between SQL Server 2000, SQL Server 2005 RTM and SQL Server 2005 SP2 blog post. In real life, when I was troubleshooting this problem, I spent a week trying to chase down the cause of the disk I/O bottleneck with our Server Admin and SAN Admin, and there wasn’t much that could be done immediately there, so I finally asked if we could increase the memory on the server to 16GB, which did fix the problem. It wasn’t until I had this same problem occur on another system that I actually figured out how to really troubleshoot this down to the root cause.  I couldn’t believe the size of the plan cache on the server with 16GB of memory when I actually learned about this and went back to look at it. SQL Server is constantly telling a story to anyone that will listen. As the DBA, you have to sit back and listen to all that it’s telling you and then evaluate the big picture and how all the data you can gather from SQL about performance relate to each other. One of the greatest tools out there is actually a free in the form of Diagnostic Scripts for SQL Server 2005 and 2008, created by MVP Glenn Alan Berry. Glenn’s scripts collect a majority of the information that SQL has to offer for rapid troubleshooting of problems, and he includes a lot of notes about what the outputs of each individual query might be telling you. When I read Pinal’s blog post SQL SERVER – ASYNC_IO_COMPLETION – Wait Type – Day 11 of 28, I noticed that he referenced Checking Memory Related Performance Counters in his post, but there was no real explanation about why checking memory counters is so important when looking at an I/O related wait type. I thought I’d chat with him briefly on Google Talk/Twitter DM and point this out, and offer a couple of other points I noted, so that he could add the information to his blog post if he found it useful.  Instead he asked that I write a guest blog for this. I am honored to be a guest blogger, and to be able to share this kind of information with the community. The information contained in this blog post is a glimpse at how I do troubleshooting almost every day of the week in my own environment. SQL Server provides us with a lot of information about how it is running, and where it may be having problems, it is up to us to play detective and find out how all that information comes together to tell us what’s really the problem. This blog post is written by Jonathan Kehayias (Blog | Twitter). Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: MVP, Pinal Dave, PostADay, Readers Contribution, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • SQL SERVER – Guest Posts – Feodor Georgiev – The Context of Our Database Environment – Going Beyond the Internal SQL Server Waits – Wait Type – Day 21 of 28

    - by pinaldave
    This guest post is submitted by Feodor. Feodor Georgiev is a SQL Server database specialist with extensive experience of thinking both within and outside the box. He has wide experience of different systems and solutions in the fields of architecture, scalability, performance, etc. Feodor has experience with SQL Server 2000 and later versions, and is certified in SQL Server 2008. In this article Feodor explains the server-client-server process, and concentrated on the mutual waits between client and SQL Server. This is essential in grasping the concept of waits in a ‘global’ application plan. Recently I was asked to write a blog post about the wait statistics in SQL Server and since I had been thinking about writing it for quite some time now, here it is. It is a wide-spread idea that the wait statistics in SQL Server will tell you everything about your performance. Well, almost. Or should I say – barely. The reason for this is that SQL Server is always a part of a bigger system – there are always other players in the game: whether it is a client application, web service, any other kind of data import/export process and so on. In short, the SQL Server surroundings look like this: This means that SQL Server, aside from its internal waits, also depends on external waits and settings. As we can see in the picture above, SQL Server needs to have an interface in order to communicate with the surrounding clients over the network. For this communication, SQL Server uses protocol interfaces. I will not go into detail about which protocols are best, but you can read this article. Also, review the information about the TDS (Tabular data stream). As we all know, our system is only as fast as its slowest component. This means that when we look at our environment as a whole, the SQL Server might be a victim of external pressure, no matter how well we have tuned our database server performance. Let’s dive into an example: let’s say that we have a web server, hosting a web application which is using data from our SQL Server, hosted on another server. The network card of the web server for some reason is malfunctioning (think of a hardware failure, driver failure, or just improper setup) and does not send/receive data faster than 10Mbs. On the other end, our SQL Server will not be able to send/receive data at a faster rate either. This means that the application users will notify the support team and will say: “My data is coming very slow.” Now, let’s move on to a bit more exciting example: imagine that there is a similar setup as the example above – one web server and one database server, and the application is not using any stored procedure calls, but instead for every user request the application is sending 80kb query over the network to the SQL Server. (I really thought this does not happen in real life until I saw it one day.) So, what happens in this case? To make things worse, let’s say that the 80kb query text is submitted from the application to the SQL Server at least 100 times per minute, and as often as 300 times per minute in peak times. Here is what happens: in order for this query to reach the SQL Server, it will have to be broken into a of number network packets (according to the packet size settings) – and will travel over the network. On the other side, our SQL Server network card will receive the packets, will pass them to our network layer, the packets will get assembled, and eventually SQL Server will start processing the query – parsing, allegorizing, generating the query execution plan and so on. So far, we have already had a serious network overhead by waiting for the packets to reach our Database Engine. There will certainly be some processing overhead – until the database engine deals with the 80kb query and its 20 subqueries. The waits you see in the DMVs are actually collected from the point the query reaches the SQL Server and the packets are assembled. Let’s say that our query is processed and it finally returns 15000 rows. These rows have a certain size as well, depending on the data types returned. This means that the data will have converted to packages (depending on the network size package settings) and will have to reach the application server. There will also be waits, however, this time you will be able to see a wait type in the DMVs called ASYNC_NETWORK_IO. What this wait type indicates is that the client is not consuming the data fast enough and the network buffers are filling up. Recently Pinal Dave posted a blog on Client Statistics. What Client Statistics does is captures the physical flow characteristics of the query between the client(Management Studio, in this case) and the server and back to the client. As you see in the image, there are three categories: Query Profile Statistics, Network Statistics and Time Statistics. Number of server roundtrips–a roundtrip consists of a request sent to the server and a reply from the server to the client. For example, if your query has three select statements, and they are separated by ‘GO’ command, then there will be three different roundtrips. TDS Packets sent from the client – TDS (tabular data stream) is the language which SQL Server speaks, and in order for applications to communicate with SQL Server, they need to pack the requests in TDS packets. TDS Packets sent from the client is the number of packets sent from the client; in case the request is large, then it may need more buffers, and eventually might even need more server roundtrips. TDS packets received from server –is the TDS packets sent by the server to the client during the query execution. Bytes sent from client – is the volume of the data set to our SQL Server, measured in bytes; i.e. how big of a query we have sent to the SQL Server. This is why it is best to use stored procedures, since the reusable code (which already exists as an object in the SQL Server) will only be called as a name of procedure + parameters, and this will minimize the network pressure. Bytes received from server – is the amount of data the SQL Server has sent to the client, measured in bytes. Depending on the number of rows and the datatypes involved, this number will vary. But still, think about the network load when you request data from SQL Server. Client processing time – is the amount of time spent in milliseconds between the first received response packet and the last received response packet by the client. Wait time on server replies – is the time in milliseconds between the last request packet which left the client and the first response packet which came back from the server to the client. Total execution time – is the sum of client processing time and wait time on server replies (the SQL Server internal processing time) Here is an illustration of the Client-server communication model which should help you understand the mutual waits in a client-server environment. Keep in mind that a query with a large ‘wait time on server replies’ means the server took a long time to produce the very first row. This is usual on queries that have operators that need the entire sub-query to evaluate before they proceed (for example, sort and top operators). However, a query with a very short ‘wait time on server replies’ means that the query was able to return the first row fast. However a long ‘client processing time’ does not necessarily imply the client spent a lot of time processing and the server was blocked waiting on the client. It can simply mean that the server continued to return rows from the result and this is how long it took until the very last row was returned. The bottom line is that developers and DBAs should work together and think carefully of the resource utilization in the client-server environment. From experience I can say that so far I have seen only cases when the application developers and the Database developers are on their own and do not ask questions about the other party’s world. I would recommend using the Client Statistics tool during new development to track the performance of the queries, and also to find a synchronous way of utilizing resources between the client – server – client. Here is another example: think about similar setup as above, but add another server to the game. Let’s say that we keep our media on a separate server, and together with the data from our SQL Server we need to display some images on the webpage requested by our user. No matter how simple or complicated the logic to get the images is, if the images are 500kb each our users will get the page slowly and they will still think that there is something wrong with our data. Anyway, I don’t mean to get carried away too far from SQL Server. Instead, what I would like to say is that DBAs should also be aware of ‘the big picture’. I wrote a blog post a while back on this topic, and if you are interested, you can read it here about the big picture. And finally, here are some guidelines for monitoring the network performance and improving it: Run a trace and outline all queries that return more than 1000 rows (in Profiler you can actually filter and sort the captured trace by number of returned rows). This is not a set number; it is more of a guideline. The general thought is that no application user can consume that many rows at once. Ask yourself and your fellow-developers: ‘why?’. Monitor your network counters in Perfmon: Network Interface:Output queue length, Redirector:Network errors/sec, TCPv4: Segments retransmitted/sec and so on. Make sure to establish a good friendship with your network administrator (buy them coffee, for example J ) and get into a conversation about the network settings. Have them explain to you how the network cards are setup – are they standalone, are they ‘teamed’, what are the settings – full duplex and so on. Find some time to read a bit about networking. In this short blog post I hope I have turned your attention to ‘the big picture’ and the fact that there are other factors affecting our SQL Server, aside from its internal workings. As a further reading I would still highly recommend the Wait Stats series on this blog, also I would recommend you have the coffee break conversation with your network admin as soon as possible. This guest post is written by Feodor Georgiev. Read all the post in the Wait Types and Queue series. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, Readers Contribution, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL

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  • Wait Statistics in Microsoft SQL Server

    - by KKline
    When it comes to troubleshooting in relational databases, there's no better place to start than wait statistics. In a nutshell, a wait statistic is an internal counter that tells you how long the database spent waiting for a particular resource, activity, or process. Since wait statistics are categorized by type, one look will quickly tell the variety of problem that needs your attention, assuming you know meaning for Microsoft's lingo for each wait type....(read more)

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  • SQL SERVER – IO_COMPLETION – Wait Type – Day 10 of 28

    - by pinaldave
    For any good system three things are vital: CPU, Memory and IO (disk). Among these three, IO is the most crucial factor of SQL Server. Looking at real-world cases, I do not see IT people upgrading CPU and Memory frequently. However, the disk is often upgraded for either improving the space, speed or throughput. Today we will look at an IO-related wait types. From Book On-Line: Occurs while waiting for I/O operations to complete. This wait type generally represents non-data page I/Os. Data page I/O completion waits appear as PAGEIOLATCH_* waits. IO_COMPLETION Explanation: Any tasks are waiting for I/O to finish. This is a good indication that IO needs to be looked over here. Reducing IO_COMPLETION wait: When it is an issue concerning the IO, one should look at the following things related to IO subsystem: Proper placing of the files is very important. We should check the file system for proper placement of files – LDF and MDF on a separate drive, TempDB on another separate drive, hot spot tables on separate filegroup (and on separate disk),etc. Check the File Statistics and see if there is higher IO Read and IO Write Stall SQL SERVER – Get File Statistics Using fn_virtualfilestats. Check event log and error log for any errors or warnings related to IO. If you are using SAN (Storage Area Network), check the throughput of the SAN system as well as the configuration of the HBA Queue Depth. In one of my recent projects, the SAN was performing really badly so the SAN administrator did not accept it. After some investigations, he agreed to change the HBA Queue Depth on development (test environment) set up and as soon as we changed the HBA Queue Depth to quite a higher value, there was a sudden big improvement in the performance. It is very possible that there are no proper indexes in the system and there are lots of table scans and heap scans. Creating proper index can reduce the IO bandwidth considerably. If SQL Server can use appropriate cover index instead of clustered index, it can effectively reduce lots of CPU, Memory and IO (considering cover index has lesser columns than cluster table and all other; it depends upon the situation). You can refer to the two articles that I wrote; they are about how to optimize indexes: Create Missing Indexes Drop Unused Indexes Checking Memory Related Perfmon Counters SQLServer: Memory Manager\Memory Grants Pending (Consistent higher value than 0-2) SQLServer: Memory Manager\Memory Grants Outstanding (Consistent higher value, Benchmark) SQLServer: Buffer Manager\Buffer Hit Cache Ratio (Higher is better, greater than 90% for usually smooth running system) SQLServer: Buffer Manager\Page Life Expectancy (Consistent lower value than 300 seconds) Memory: Available Mbytes (Information only) Memory: Page Faults/sec (Benchmark only) Memory: Pages/sec (Benchmark only) Checking Disk Related Perfmon Counters Average Disk sec/Read (Consistent higher value than 4-8 millisecond is not good) Average Disk sec/Write (Consistent higher value than 4-8 millisecond is not good) Average Disk Read/Write Queue Length (Consistent higher value than benchmark is not good) Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading Book OnLine for further clarification. All the discussions of Wait Stats in this blog are generic and vary from system to system. It is recommended that you test this on a development server before implementing it to a production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Types, SQL White Papers, T SQL, Technology

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  • European e-government Action Plan all about interoperability

    - by trond-arne.undheim
    Yesterday, the European Commission released its European eGovernment Action Plan for 2011-2015. The plan includes measures on providing deeper user empowerment, enhancing the Internal Market, more efficiency and effectiveness of public administrations, and putting in place pre-conditions for developing e-government. The Good - Defines interoperability very clearly. Calls interoperability "a pre-condition for cross-border eGovernment services" (a very strong formulation) and says interoperability "is supported by open specifications". - Uses the terminology "open specifications" which, let's face it, is pretty close to "open standards" which is the term the rest of the world would use. - Confirms that Member States are fully committed to the political priorities of the Malmö Declaration (which was all about open standards) including the very strong action: by 2013: All Member States will have incorporated the political priorities of the Malmö Declaration in their national strategies. Such tight Action Plan integration between Commission and Member State priorities has seldom been attempted before, particularly not in a field where European legal competence is virtually non-existent. What we see now, is the subtle force of soft power rather than the rough force of regulation. In this case, it is the Member States who want Europe to take the lead. Very refreshing! Some quotes that show the commitment to interoperability and open specifications: "The emergence of innovative technologies such as "service-oriented architectures" (SOA), or "clouds" of services,  together with more open specifications which allow for greater sharing, re-use and interoperability reinforce the ability of ICT to play a key role in this quest for effficiency in the public sector." (p.4) "Interoperability is supported through open specifications" (p.13) 2.4.1. Open Specifications and Interoperability (p.13 has a whole section dedicated to this important topic. Open specifications and interoperability are nearly 100% interrelated): "Interoperability is the ability of systems and machines to exchange, process and correctly interpret information. It is more than just a technical challenge, as it also involves legal, organisational and semantic aspects of handling  data" (p.13) "standards and  open platforms offer opportunities for more cost-effective use of resources and delivery of services" (p.13). The Bad Shies away from defining open standards, or even open specifications, the EU's preferred term for the key enabler of interoperability. Verdict 90/100, a very respectable score.

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  • SQLAuthority News – I am Presenting 2 Sessions at TechEd India

    - by pinaldave
    TechED is the event which I am always excited about. It is one of the largest technology in India. Microsoft Tech Ed India 2011 is the premier technical education and networking event for tech professionals interested in learning, connecting and exploring a broad set of current and soon-to-be released Microsoft technologies, tools, platforms and services. I am going to speak at the TechED on two very interesting and advanced subjects. Venue: The LaLiT Ashok Kumara Krupa High Grounds Bangalore – 560001, Karnataka, India Sessions Date: March 25, 2011 Understanding SQL Server Behavioral Pattern – SQL Server Extended Events Date and Time: March 25, 2011 12:00 PM to 01:00 PM History repeats itself! SQL Server 2008 has introduced a very powerful, yet very minimal reoccurring feature called Extended Events. This advanced session will teach experienced administrators’ capabilities that were not possible before. From T-SQL error to CPU bottleneck, error login to deadlocks –Extended Event can detect it for you. Understanding the pattern of events can prevent future mistakes. SQL Server Waits and Queues – Your Gateway to Perf. Troubleshooting Date and Time: March 25, 2011 04:15 PM to 05:15 PM Just like a horoscope, SQL Server Waits and Queues can reveal your past, explain your present and predict your future. SQL Server Performance Tuning uses the Waits and Queues as a proven method to identify the best opportunities to improve performance. A glance at Wait Types can tell where there is a bottleneck. Learn how to identify bottlenecks and potential resolutions in this fast paced, advanced performance tuning session. My session will be on the third day of the event and I am very sure that everybody will be in groove to learn new interesting subjects. I will have few give-away during and at the end of the session. I will not tell you what I will have but it will be for sure something you will love to have. Please make a point and reserve above time slots to attend my session. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: About Me, Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology Tagged: SQL Extended Events

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  • SQL SERVER – Speed Up! – Parallel Processes and Unparalleled Performance – TechEd 2012 India

    - by pinaldave
    TechEd India 2012 is just around the corner and I will be presenting there on two different session. SQL Server Performance Tuning is a very challenging subject that requires expertise in Database Administration and Database Development. I always have enjoyed talking about SQL Server Performance tuning subject. Just like doctors I like to call my every attempt to improve the performance of SQL Server queries and database server as a practice too. I have been working with SQL Server for more than 8 years and I believe that many of the performance tuning concept I have mastered. However, performance tuning is not a simple subject. However there are occasions when I feel stumped, there are occasional when I am not sure what should be the next step. When I face situation where I cannot figure things out easily, it makes me most happy because I clearly see this as a learning opportunity. I have been presenting in TechEd India for last three years. This is my fourth time opportunity to present a technical session on SQL Server. Just like every other year, I decided to present something different, something which I have spend years of learning. This time, I am going to present about parallel processes. It is widely believed that more the CPU will improve performance of the server. It is true in many cases. However, there are cases when limiting the CPU usages have improved overall health of the server. I will be presenting on the subject of Parallel Processes and its effects. I have spent more than a year working on this subject only. After working on various queries on multi-CPU systems I have personally learned few things. In coming TechEd session, I am going to share my experience with parallel processes and performance tuning. Session Details Title: Speed Up! – Parallel Processes and Unparalleled Performance (Add to Calendar) Abstract: “More CPU More Performance” – A  very common understanding is that usage of multiple CPUs can improve the performance of the query. To get maximum performance out of any query – one has to master various aspects of the parallel processes. In this deep dive session, we will explore this complex subject with a very simple interactive demo. An attendee will walk away with proper understanding of CX_PACKET wait types, MAXDOP, parallelism threshold and various other concepts. Date and Time: March 23, 2012, 12:15 to 13:15 Location: Hotel Lalit Ashok - Kumara Krupa High Grounds, Bengaluru – 560001, Karnataka, India. Add to Calendar Please submit your questions in the comments area and I will be for sure discussing them during my session. If I pick your question to discuss during my session, here is your gift I commit right now – SQL Server Interview Questions and Answers Book. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology Tagged: TechEd, TechEdIn

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  • SQLAuthority News – Community Tech Days – TechEd on The Road – Ahmedabad – June 11, 2011

    - by pinaldave
    TechEd on Road is back! In Ahmedabad June 11, 2011! Inviting all Professional Developers, Project Managers, Architects, IT Managers, IT Administrators and Implementers of Ahmedabad to be a part of Tech•Ed on the Road, on 11th June, 2011. We have put together the best sessions from Tech•Ed India 2011 for you in your city. Focal point will be technologies like Database and BI, Windows 7, ASP.NET. REGISTER HERE! Venue: Venue: Ahmedabad Management Association (AMA) Dr. Vikram Sarabhai Marg, University Area, Ahmedabad, Gujarat 380 015 Time: 9:30AM – 5:30PM The biggest attraction of the event is session HTML5 – Future of the Web by Harish Vaidyanathan. He is Evangelist Lead in Microsoft and hands on developer himself. I strongly urge all of you to attend his session to understand direction of the web and Microsoft’s take on the subject. I (Pinal Dave) will be presenting on the session of SQL Server Performance Tuning and Jacob Sebastian will be presenting on T-SQL Worst Practices. Do not miss this opportunity. Those who have attended in the past know that from last two years the venue is jam packed in first few minutes. Do come in early to get better seat and reserve your spot. We will have QUIZ during the event and we will have various gifts – Watches, USB Drives, T-Shirts and many more interesting gifts. Refer the agenda today and register right away. There will be no video recording so come and visit the event in person. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: About Me, Best Practices, Database, DBA, MVP, Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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  • How Many States Does an Activity Have?

    - by Android Eve
    The Activity lifecycle section in the Application Fundamentals tutorial states that there are 3 states: An activity has essentially three states: (1. active/running 2. paused 3. stopped) But then as I continued reading the actual Activity class documentation, the Activity Lifecycle section states that there are 4 state: An activity has essentially four states: (1. active/running 2. paused 3. stopped 4. "dropped"?) Both sources (on the same website) agree about the first 3, but the 4th one is only mentioned in the class documentation and is unnamed. So, are there really 4 states or only 3? If there are 4, what is the name of the 4th one? Please help me understand this discrepancy. Also, highlighted colored blocks in this beautiful and very informative flowchart don't seem to correspond to the states. Where, in the flowchart, would you mark the 3 or 4 states?

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  • Windows wait command till a system time

    - by user53864
    I have made a batch script for backup recently. Somewhere in the middle of script I'll have to wait for some time to be reached and then resume the next line of the script. I've scheduled the script at 4:00PM and after the wait command the next line should start at exactly 5:30PM. I thought of using SLEEP command but it's not sure that the commands used before the wait command will end up at certain time(due to inconsistent file sizes) but it's sure that they will be done by 5:00 or 5:10 and next it should execute wait command which waits for certain system clock. I'm checking if there is any command that waits or sleeps until the time specified reaches the system time and resumes there after. Anybody came across this situation and how was that resolved?

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  • Java threads, wait time always 00:00:00-Producer/Consumer

    - by user3742254
    I am currently doing a producer consumer problem with a number of threads and have had to set priorities and waits to them to ensure that one thread, the security thread, runs last. I have managed to do this and I have managed to get the buffer working. The last thing that I am required to do is to show the wait time of threads that are too large for the buffer and to calculate the average wait time. I have included code to do so, but everything I run the program, the wait time is always returned as 00:00:00, and by extension, the average is returned as the same. I was speaking to one of my colleagues who said that it is not a matter of the code but rather a matter of the computer needing to work off of one processor, which can be adjusted in the task manager settings. He has an HP like myself but his program prints the wait time 180 times, whereas mine prints usually about 3-7 times and is only 00:00:01 on one instance before finishing when I have made the processor adjustments. My other colleague has an iMac and hers puts out an average of 42:00:34(42 minutes??) I am very confused about this because I can see no difference between our codes and like my colleague said, I was wondering is it a computer issue. I am obviously concerned as I wanted to make sure that my code correctly calculated an average wait time, but that is impossible to tell when the wait times always show as 00:00:00. To calculate the thread duration, including the time it entered and exited the buffer was done by using a timestamp import, and then subtracting start time from end time. Is my code correct for this issue or is there something which is missing? I would be very grateful for any solutions. Below is my code: My buffer class package com.Com813cw; import java.text.DateFormat; import java.text.SimpleDateFormat; /** * Created by Rory on 10/08/2014. */ class Buffer { private int contents, count = 0, process = 200; private int totalRam = 1000; private boolean available = false; private long start, end, wait, request = 0; private DateFormat time = new SimpleDateFormat("ss:SSS"); public int avWaitTime =0; public void average(){ System.out.println("Average Application Request wait time: "+ time.format(request/count)); } public synchronized int get() { while (process <= 500) { try { wait(); } catch (InterruptedException e) { } } process -= 200; System.out.println("CPU After Process " + process); notifyAll(); return contents; } public synchronized void put(int value) { if (process <= 500) { process += value; } else { start = System.currentTimeMillis(); try { wait(); } catch (InterruptedException e) { } end = System.currentTimeMillis(); wait = end - start; count++; request += wait; System.out.println("Application Request Wait Time: " + time.format(wait)); process += value; contents = value; calcWait(wait, count); } notifyAll(); } public void calcWait(long wait, int count){ this.avWaitTime = (int) (wait/count); } public void printWait(){ System.out.println("Wait time is " + time.format(this.avWaitTime)); } } My spotify class package com.Com813cw; import java.sql.Timestamp; /** * Created by Rory on 11/08/2014. */ class Spotify extends Thread { private Buffer buffer; private int number; private int bytes = 250; public Spotify(Buffer c, int number) { buffer = c; this.number = number; } long startTime = System.currentTimeMillis(); public void run() { for (int i = 0; i < 20; i++) { buffer.put(bytes); System.out.println(getName() + this.number + " put: " + bytes + " bytes "); try { sleep(1000); } catch (InterruptedException e) { } } long endTime = System.currentTimeMillis(); long timeTaken = endTime - startTime; java.util.Date date = new java.util.Date(); System.out.println("-----------------------------"); System.out.println("Spotify has finished executing."); System.out.println("Time taken to execute was " + timeTaken + " milliseconds"); System.out.println("Time that Spotify thread exited Buffer was " + new Timestamp(date.getTime())); System.out.println("-----------------------------"); } } My BubbleWitch class package com.Com813cw; import java.lang.*; import java.lang.System; import java.sql.Timestamp; /** * Created by Rory on 10/08/2014. */ class BubbleWitch2 extends Thread { private Buffer buffer; private int number; private int bytes = 100; public BubbleWitch2(Buffer c, int number) { buffer = c; this.number=number ; } long startTime = System.currentTimeMillis(); public void run() { for (int i = 0; i < 10; i++) { buffer.put(bytes); System.out.println(getName() + this.number + " put: " + bytes + " bytes "); try { sleep(1000); } catch (InterruptedException e) { } } long endTime = System.currentTimeMillis(); long timeTaken = endTime - startTime; java.util.Date date = new java.util.Date(); System.out.println("-----------------------------"); System.out.println("BubbleWitch2 has finished executing."); System.out.println("Time taken to execute was " +timeTaken+ " milliseconds"); System.out.println("Time Bubblewitch2 thread exited Buffer was " + new Timestamp(date.getTime())); System.out.println("-----------------------------"); } } My Test class package com.Com813cw; /** * Created by Rory on 10/08/2014. */ public class ProducerConsumerTest { public static void main(String[] args) throws InterruptedException { Buffer c = new Buffer(); BubbleWitch2 p1 = new BubbleWitch2(c,1); Processor c1 = new Processor(c, 1); Spotify p2 = new Spotify(c, 2); SystemManagement p3 = new SystemManagement(c, 3); SecurityUpdate p4 = new SecurityUpdate(c, 4, p1, p2, p3); p1.setName("BubbleWitch2 "); p2.setName("Spotify "); p3.setName("System Management "); p4.setName("Security Update "); p1.setPriority(10); p2.setPriority(10); p3.setPriority(10); p4.setPriority(5); c1.start(); p1.start(); p2.start(); p3.start(); p4.start(); p2.join(); p3.join(); p4.join(); c.average(); System.exit(0); } } My security update package com.Com813cw; import java.lang.*; import java.lang.System; import java.sql.Timestamp; /** * Created by Rory on 11/08/2014. */ class SecurityUpdate extends Thread { private Buffer buffer; private int number; private int bytes = 150; private int process = 0; public SecurityUpdate(Buffer c, int number, BubbleWitch2 bubbleWitch2, Spotify spotify, SystemManagement systemManagement) throws InterruptedException { buffer = c; this.number = number; bubbleWitch2.join(); spotify.join(); systemManagement.join(); } long startTime = System.currentTimeMillis(); public void run() { for (int i = 0; i < 15; i++) { buffer.put(bytes); System.out.println(getName() + this.number + " put: " + bytes + " bytes"); try { sleep(1500); } catch (InterruptedException e) { } } long endTime = System.currentTimeMillis(); long timeTaken = endTime - startTime; java.util.Date date = new java.util.Date(); System.out.println("-----------------------------"); System.out.println("Security Update has finished executing."); System.out.println("Time taken to execute was " + timeTaken + " milliseconds"); System.out.println("Time that SecurityUpdate thread exited Buffer was " + new Timestamp(date.getTime())); System.out.println("------------------------------"); } } I'd be grateful as I said for any help as this is the last and most frustrating obstacle.

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  • A lot of TCP: time wait bucket table overflow in CentOS 6

    - by divaka
    we have the following output from dmesg: __ratelimit: 33491 callbacks suppressed TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow Also we have the following setting: cat /proc/sys/net/ipv4/tcp_max_tw_buckets 524288 We are under some kind of attack, but we could not detect what cause this problem?

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  • Questions about game states

    - by MrPlow
    I'm trying to make a framework for a game I've wanted to do for quite a while. The first thing that I decided to implement was a state system for game states. When my "original" idea of having a doubly linked list of game states failed I found This blog and liked the idea of a stack based game state manager. However there were a few things I found weird: Instead of RAII two class methods are used to initialize and destroy the state Every game state class is a singleton(and singletons are bad aren't they?) Every GameState object is static So I took the idea and altered a few things and got this: GameState.h class GameState { private: bool m_paused; protected: StateManager& m_manager; public: GameState(StateManager& manager) : m_manager(manager), m_paused(false){} virtual ~GameState() {} virtual void update() = 0; virtual void draw() = 0; virtual void handleEvents() = 0; void pause() { m_paused = true; } void resume() { m_paused = false; } void changeState(std::unique_ptr<GameState> state) { m_manager.changeState(std::move(state)); } }; StateManager.h class GameState; class StateManager { private: std::vector< std::unique_ptr<GameState> > m_gameStates; public: StateManager(); void changeState(std::unique_ptr<GameState> state); void StateManager::pushState(std::unique_ptr<GameState> state); void popState(); void update(); void draw(); void handleEvents(); }; StateManager.cpp StateManager::StateManager() {} void StateManager::changeState( std::unique_ptr<GameState> state ) { if(!m_gameStates.empty()) { m_gameStates.pop_back(); } m_gameStates.push_back( std::move(state) ); } void StateManager::pushState(std::unique_ptr<GameState> state) { if(!m_gameStates.empty()) { m_gameStates.back()->pause(); } m_gameStates.push_back( std::move(state) ); } void StateManager::popState() { if(!m_gameStates.empty()) m_gameStates.pop_back(); } void StateManager::update() { if(!m_gameStates.empty()) m_gameStates.back()->update(); } void StateManager::draw() { if(!m_gameStates.empty()) m_gameStates.back()->draw(); } void StateManager::handleEvents() { if(!m_gameStates.empty()) m_gameStates.back()->handleEvents(); } And it's used like this: main.cpp StateManager states; states.changeState( std::unique_ptr<GameState>(new GameStateIntro(states)) ); while(gamewindow::gameWindow.isOpen()) { states.handleEvents(); states.update(); states.draw(); } Constructors/Destructors are used to create/destroy states instead of specialized class methods, state objects are no longer static but

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  • Java's Object.wait method with nanoseconds: Is this a joke or am I missing something

    - by Krumia
    I was checking out the Java API source code (Java 8) just out of curiosity. And I found this in java/lang/Object.java. There are three methods named wait: public final native void wait(long timeout): This is the core of all wait methods, which has a native implementation. public final void wait(): Just calls wait(0). And then there is public final void wait(long timeout, int nanos). The JavaDoc for the particular method tells me that, This method is similar to the wait method of one argument, but it allows finer control over the amount of time to wait for a notification before giving up. The amount of real time, measured in nanoseconds, is given by: 1000000*timeout+nanos But this is how the methods achieves "finer control over the amount of time to wait": if (nanos >= 500000 || (nanos != 0 && timeout == 0)) { timeout++; } wait(timeout); So this method basically does a crude rounding up of nanoseconds to milliseconds. Not to mention that anything below 500000ns/0.5ms will be ignored. Is this piece of code bad/unnecessary code, or am I missing some unseen virtue of declaring this method, and it's no argument cousin as the way they are?

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  • Displaying wait cursor in while backgroundworker is running

    - by arc1880
    During the start of my windows application, I have to make a call to a web service to retrieve some default data to load onto my application. During the load of the form, I run a backgroundworker to retrieve this data. I want to display the wait cursor until this data is retrieved. How would I do this? I've tried setting the wait cursor before calling the backgroundworker to run. When I report a progress of 100 then I set it back to the default cursor. The wait cursor comes up but when I move the mouse it disappears. Environment: Windows 7 Pro 64-bit VS2010 C# .NET 4.0 Windows Forms EDIT: I am setting the cursor the way Jay Riggs suggested. It only works if I don't move the mouse. **UPDATE: I have created a button click which does the following: When I do the button click and move my mouse, the wait cursor appears regardless if I move my mouse or not. void BtnClick() { Cursor = Cursors.WaitCursor; Thread.Sleep(8000); Cursor = Cursors.Default; } If I do the following: I see the wait cursor and when I move the mouse it disappears inside the form. If I move to my status bar or the menu bar the wait cursor appears. Cursor = Cursors.WaitCursor; if (!backgroundWorker.IsBusy) { backGroundWorker.RunWorkerAsync(); } void backGroundWorkerDoWork(object sender, DoWorkEventArgs e) { Thread.Sleep(8000); } void backGroundWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { Cursor = Cursors.Default; } If I do the following: The wait cursor appears and when I move the mouse it still appears but will sometimes flicker off and on when moving in text fields. if (!backgroundWorker.IsBusy) { backGroundWorker.RunWorkerAsync(); } void backGroundWorkerDoWork(object sender, DoWorkEventArgs e) { UseWaitCursor = true; Thread.Sleep(8000); } void backGroundWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { UseWaitCursor = false; }

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  • Why wait should always be in synchronized block

    - by diy
    Hi gents, We all know that in order to invoke Object.wait() , this call must be placed in synchronized block,otherwise,IllegalMonitorStateException is thrown.But what's the reason for making this restriction?I know that wait() releases the monitor, but why do we need to explicitly acquire the monitor by making particular block synchronized and then release the monitor by calling wait() ? What is the potential damage if it was possible to invoke wait() outside synch block, retaining it's semantics - suspending the caller thread ? Thanks in advance

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  • WPF Show wait cursor before application fully loads

    - by e28Makaveli
    I want to show the wait cursor before my WPF application, composed using CAL, fully loads. In the constructor of the main window, I have the following code: public MainWindow([Dependency] IUnityContainer container) { InitializeComponent(); Cursor = System.Windows.Input.Cursors.Wait; Mouse.OverrideCursor = System.Windows.Input.Cursors.Wait; ForceCursor = true; //this.Cursor = System.Windows.Input.Cursors.AppStarting; // event subscriptions PresenterBase.EventAggregate.GetEvent<ModulesLoadedEvent>().Subscribe(OnModulesLoaded); } After all modules have been loaded, the following handler is invoked: private void OnModulesLoaded(EventArgs e) { allModulesLoaded = true; Mouse.OverrideCursor = null; Cursor = System.Windows.Input.Cursors.Arrow; } Problem is, I do not see this wait cursor. What I am missing here? FWIW, I got a hint from this post http://stackoverflow.com/questions/2078766/showing-the-wait-cursor TIA.

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  • Can a thread call wait() on two locks at once in Java (6)

    - by Dr. Monkey
    I've just been messing around with threads in Java to get my head around them (it seems like the best way to do so) and now understand what's going on with synchronize, wait() and notify(). I'm curious about whether there's a way to wait() on two resources at once. I think the following won't quite do what I'm thinking of: synchronized(token1) { synchronized(token2) { token1.wait(); token2.wait(); //won't run until token1 is returned System.out.println("I got both tokens back"); } } In this (very contrived) case token2 will be held until token1 is returned, then token1 will be held until token2 is returned. The goal is to release both token1 and token2, then resume when both are available (note that moving the token1.wait() outside the inner synchronized loop is not what I'm getting at). A loop checking whether both are available might be more appropriate to achieve this behaviour (would this be getting near the idea of double-check locking?), but would use up extra resources - I'm not after a definitive solution since this is just to satisfy my curiosity.

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  • Data-driven animation states

    - by user8363
    I'm trying to handle animations in a 2D game engine hobby project, without hard-coding them. Hard coding animation states seems like a common but very strange phenomenon, to me. A little background: I'm working with an entity system where components are bags of data and subsystems act upon them. I chose to use a polling system to update animation states. With animation states I mean: "walking_left", "running_left", "walking_right", "shooting", ... My idea to handle animations was to design it as a data driven model. Data could be stored in an xml file, a rdbms, ... And could be loaded at the start of a game / level/ ... This way you can easily edit animations and transitions without having to go change the code everywhere in your game. As an example I made an xml draft of the data definitions I had in mind. One very important piece of data would simply be the description of an animation. An animation would have a unique id (a descriptive name). It would hold a reference id to an image (the sprite sheet it uses, because different animations may use different sprite sheets). The frames per second to run the animation on. The "replay" here defines if an animation should be run once or infinitely. Then I defined a list of rectangles as frames. <animation id='WIZARD_WALK_LEFT'> <image id='WIZARD_WALKING' /> <fps>50</fps> <replay>true</replay> <frames> <rectangle> <x>0</x> <y>0</y> <width>45</width> <height>45</height> </rectangle> <rectangle> <x>45</x> <y>0</y> <width>45</width> <height>45</height> </rectangle> </frames> </animation> Animation data would be loaded and held in an animation resource pool and referenced by game entities that are using it. It would be treated as a resource like an image, a sound, a texture, ... The second piece of data to define would be a state machine to handle animation states and transitions. This defines each state a game entity can be in, which states it can transition to and what triggers that state change. This state machine would differ from entity to entity. Because a bird might have states "walking" and "flying" while a human would only have the state "walking". However it could be shared by different entities because multiple humans will probably have the same states (especially when you define some common NPCs like monsters, etc). Additionally an orc might have the same states as a human. Just to demonstrate that this state definition might be shared but only by a select group of game entities. <state id='IDLE'> <event trigger='LEFT_DOWN' goto='MOVING_LEFT' /> <event trigger='RIGHT_DOWN' goto='MOVING_RIGHT' /> </state> <state id='MOVING_LEFT'> <event trigger='LEFT_UP' goto='IDLE' /> <event trigger='RIGHT_DOWN' goto='MOVING_RIGHT' /> </state> <state id='MOVING_RIGHT'> <event trigger='RIGHT_UP' goto='IDLE' /> <event trigger='LEFT_DOWN' goto='MOVING_LEFT' /> </state> These states can be handled by a polling system. Each game tick it grabs the current state of a game entity and checks all triggers. If a condition is met it changes the entity's state to the "goto" state. The last part I was struggling with was how to bind animation data and animation states to an entity. The most logical approach seemed to me to add a pointer to the state machine data an entity uses and to define for each state in that machine what animation it uses. Here is an xml example how I would define the animation behavior and graphical representation of some common entities in a game, by addressing animation state and animation data id. Note that both "wizard" and "orc" have the same animation states but a different animation. Also, a different animation could mean a different sprite sheet, or even a different sequence of animations (an animation could be longer or shorter). <entity name="wizard"> <state id="IDLE" animation="WIZARD_IDLE" /> <state id="MOVING_LEFT" animation="WIZARD_WALK_LEFT" /> </entity> <entity name="orc"> <state id="IDLE" animation="ORC_IDLE" /> <state id="MOVING_LEFT" animation="ORC_WALK_LEFT" /> </entity> When the entity is being created it would add a list of states with state machine data and an animation data reference. In the future I would use the entity system to build whole entities by defining components in a similar xml format. -- This is what I have come up with after some research. However I had some trouble getting my head around it, so I was hoping op some feedback. Is there something here what doesn't make sense, or is there a better way to handle these things? I grasped the idea of iterating through frames but I'm having trouble to take it a step further and this is my attempt to do that.

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  • Apache on Windows random long wait times

    - by Jaxbot
    I have a development machine with Apache installed as a service on Windows. The installation is fresh out of the box, with no changes to configuration aside from adding the PHP module. From day one, I've had a problem that looks like this: Essentially, Apache is freezing for about 11 seconds before replying on random requests. This appears to happen more frequently when the host hasn't been connected to in a while, but this is not always the case. I've eliminated MySQL, PHP, and the specific application; this long wait problem will occur even when loading a static file such as favicon.ico. Thus, the only factor remaining is Apache, which is freezing for consistently around 10-11 seconds before replying. The problem is not the DNS problem that many people point to; as you can see, the DNS lookup is instant, and the problem occurs both on localhost and 127.0.0.1. Thanks for the time.

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