InstantForum.NET v2.9.0SQLServerCentralhttp://www.sqlservercentral.com/Forums/notifications@sqlservercentral.comWed, 19 Jun 2013 11:39:17 GMT20http://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspxI've been going through this a lot lately and thought I'd share just in case. I don't (yet, but I will) know all the details because the Infrastructure Team owns the resources and "the problem". They have a DR site setup and they use some sort of SAN based replication to keep them in sync. It apparently has some sort of a log (file) and replicates things asynchronusly through the log as a buffer. Everything works great and fast except if the log gets too far behind (typical because of nightly jobs) and the replication goes into what is known as the "synchronus" mode. When it does that, not only do things have to commit on the local server but they also have to commit on the remote server. The connections to the remote server will always be slower than the internal fiber connections we have to the SAN and form the bottle neck. Considering that the system is already way behind when it goes into the synchronuns mode, you can just imagine how slow that makes things.I'm definitely not sure if this has anything to do with your problem at all or not but you can bet my current problem doesn't show up as a "DR Replication Problem" through the system DMVs. If you have a similar thing going on, the answer won't be obvious either. Check everything and expect the unexpected.Sun, 06 Jan 2013 16:30:18 GMTJeff Modenhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspxI wil favor here to set the profiler trace ([quote]beware of filters and required columns[/quote]), see if you catch there something.Sun, 06 Jan 2013 06:53:03 GMTBhuvneshhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspxWhen looking at the wait stats, order them by the total wait time and you can see what is causing things to slow down. This is a simple version of the query:[code="sql"]SELECT TOP (10) *FROM sys.dm_os_wait_stats AS dowsORDER BY wait_time_ms DESC;[/code]The wait types themselves are not self-explanatory (although some are). You'll have to look them up to understand what's causing things to slow down on your system.Also, if you really are focused on memory, you can use sys.dm_os_ring_buffers to check for specific out of memory messages. I wrote up a method for doing that in an [url=http://www.simple-talk.com/sql/database-administration/why-is-that-sql-server-instance-under-stress/]article on Simple-Talk[/url].Sun, 06 Jan 2013 04:06:33 GMTGrant Fritcheyhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspx[/quote]Connections to the database take resources and do consume memory. That added to the waits that Grant asked about would help to understand memory pressure.Did you check with your users to find out where the app is slow?[/quote]We only found active 50 connections....which is not much. In additions to SQL using all the memory, we are also getting some error as below.'A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified) ", and also error 40 displayed in certain web application.'However, this is only happening occasionally and everything else looks fine from the database end.SueTons.Sat, 05 Jan 2013 16:04:18 GMTSQLCrazyCertifiedhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspx[quote][b]SQLCrazyCertified (1/4/2013)[/b][hr][b]SQLRNNR,[/b] There are only 50 active connections.....so, I don't think this is the issue.[b]Joie Andrew,[/b] Had complains that everything is running slow and I coudn't find anything else other than SQL using all the memory which is allocated to it.[b]GilaMonster,[/b] I am not 100% sure if it's only memory related, however, I am stuck as to what's the next step....not an exper on performance tuning.[b]Grant Fritchey,[/b] I did select * from sys.dm_os_wait_stats, now which column should I focus.I really appreciate all of you for giving me valid inputs as to where/what should I be checking. Could this be a CPU issue as well? Thanks,SueTons.[/quote]Connections to the database take resources and do consume memory. That added to the waits that Grant asked about would help to understand memory pressure.Did you check with your users to find out where the app is slow?Sat, 05 Jan 2013 15:55:13 GMTSQLRNNRhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspxOk. Thank you. I will read further.SueTons.Sat, 05 Jan 2013 15:29:06 GMTSQLCrazyCertifiedhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspx[quote][b]SQLCrazyCertified (1/5/2013)[/b][hr]So, if I understand you correctly, if SQL uses all the memory which is allocated to it, then SQL will not have enough memory to work on other outstanding processes[/quote]Huh? SQL uses its memory for all its processes, for the data cache, the plan cache and the several other caches that it has and for anything else it needs memory for.[quote]If that's the case how can you say it's the normal expected behavior?[/quote]Because it [b]is[/b] normal, expected behaviour.It would not be efficient for SQL to request memory from the OS for one process, release it when that process is done, request memory from the OS for another, release, etc. If it did, it would be spending huge amounts of time and resources requesting and and releasing memory rather than actually doing productive work. Hence it requests memory, does not release it (unless the OS complains) and manages it after that point.See the book I previously referenced, chapter 4.Sat, 05 Jan 2013 15:22:04 GMTGilaMonsterhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspx[quote][b]GilaMonster (1/5/2013)[/b][hr][quote][b]SQLCrazyCertified (1/4/2013)[/b][hr]You mentioned that SQL using all of it's memory which is allocated to it is a normal behavior, if this is true, when does the SQL release the memory?[/quote]When the OS signals that it's under memory pressure or when SQL shuts down.[quote]I know it won't release the memory to OS, but when does SQL gets more memory to do other work/processes. Please advise.[/quote]Get more memory? If it's allocated up to max server memory then it won't allocate more.[/quote]So, if I understand you correctly, if SQL uses all the memory which is allocated to it, then SQL will not have enough memory to work on other outstanding processes, so, in this scenario can we say that memory is the issue for performance issues? If that's the case how can you say it's the normal expected behavior?SueTons.Sat, 05 Jan 2013 12:50:56 GMTSQLCrazyCertifiedhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspx[quote][b]SQLCrazyCertified (1/4/2013)[/b][hr]You mentioned that SQL using all of it's memory which is allocated to it is a normal behavior, if this is true, when does the SQL release the memory?[/quote]When the OS signals that it's under memory pressure or when SQL shuts down.[quote]I know it won't release the memory to OS, but when does SQL gets more memory to do other work/processes. Please advise.[/quote]Get more memory? If it's allocated up to max server memory then it won't allocate more.Sat, 05 Jan 2013 01:46:10 GMTGilaMonsterhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspx[quote]Is there any other way to release the memory? Or how can we find why SQL server is using high memory?What are some of the causes of using high memory? Someone with experience in performance tuning, please advise.[/quote]Normal, expected behaviour. SQL uses as much memory as it is allowed to use to cache data and plans to avoid slow disk access and expensive plan recompilations. SQL will use up to the max it is allowed and that is perfectly fine. You typically want SQL to use lots of memory as it allows for efficient caching.[/quote]Gail,You mentioned that SQL using all of it's memory which is allocated to it is a normal behavior, if this is true, when does the SQL release the memory?I know it won't release the memory to OS, but when does SQL gets more memory to do other work/processes. Please advise.SueTons.Fri, 04 Jan 2013 18:33:54 GMTSQLCrazyCertifiedhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspxIt could be anything. Shotgun tuning however won't help.Chapter 1: [url]http://www.simple-talk.com/books/sql-books/troubleshooting-sql-server-a-guide-for-the-accidental-dba/[/url] Identify the problem, then consider what the potential solution is.Fri, 04 Jan 2013 09:24:52 GMTGilaMonsterhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspx[b]SQLRNNR,[/b] There are only 50 active connections.....so, I don't think this is the issue.[b]Joie Andrew,[/b] Had complains that everything is running slow and I coudn't find anything else other than SQL using all the memory which is allocated to it.[b]GilaMonster,[/b] I am not 100% sure if it's only memory related, however, I am stuck as to what's the next step....not an exper on performance tuning.[b]Grant Fritchey,[/b] I did select * from sys.dm_os_wait_stats, now which column should I focus.I really appreciate all of you for giving me valid inputs as to where/what should I be checking. Could this be a CPU issue as well? Thanks,SueTons.Fri, 04 Jan 2013 09:11:40 GMTSQLCrazyCertifiedhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspxWhat are your top 5 wait stats from sys.dm_os_wait_stats? If they are not memory related, then I doubt memory is the cause of the slow performance.Fri, 04 Jan 2013 04:15:38 GMTGrant Fritcheyhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspx[quote][b]SQLCrazyCertified (1/3/2013)[/b][hr]We have some performance issue..SQL server is running very slow due to high memory usage.[/quote]Are you sure that high memory usage is causing SQL to run slow? Cause, not correlation?[quote]Is there any other way to release the memory? Or how can we find why SQL server is using high memory?What are some of the causes of using high memory? Someone with experience in performance tuning, please advise.[/quote]Normal, expected behaviour. SQL uses as much memory as it is allowed to use to cache data and plans to avoid slow disk access and expensive plan recompilations. SQL will use up to the max it is allowed and that is perfectly fine. You typically want SQL to use lots of memory as it allows for efficient caching.Fri, 04 Jan 2013 02:24:45 GMTGilaMonsterhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspxCan you elaborate on what you mean by SQL is running slow? Specifics? You state that it is slow but there are no long running queries found.Fri, 04 Jan 2013 00:30:04 GMTJoie Andrewhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspxHow many connections? Do you have a high volume of transactions or jobs running currently?Thu, 03 Jan 2013 22:09:08 GMTSQLRNNRhttp://www.sqlservercentral.com/Forums/Topic1402644-1550-1.aspxAll,We have some performance issue..SQL server is running very slow due to high memory usage..this is a 2 node active/passive cluster. Only 1 instance is running, no other apps.Total 56GB RAM and 46GB is allocated SQL. No blocking, no open transactions, no long running queries found. Is there any other way to release the memory? Or how can we find why SQL server is using high memory?What are some of the causes of using high memory? Someone with experience in performance tuning, please advise.Thanks,SueTonsThu, 03 Jan 2013 20:17:29 GMTSQLCrazyCertified