SQL 2012 :: When Does Database Clear Buffer Cache
Sep 28, 2015
We are troubleshooting a performance problem and the test result is slow the 1st time but the subsequent runs are faster.. Logging out of application and log back in ( connecting to a new database session) did not clear the buffer cache as I thought it would.. When does the database clear the buffer cache? Is it not per database session?
I can issue CHECKPOINT and then run DBCC DROPCLEANBUFFERS to clear the buffers in the disk. But since we are testing from the application,do we need to run these commands via application code to clear buffer/per database session OR can we run these commands from a management studio session?
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Jun 22, 2015
I am using SQL 2012 and I am trying to find buffer cache usage by DB objects within a particular DB.
I am running the following query
select
name as DB,
objname as db_object_name,
COUNT(name) as cache_page_count,
COUNT('x')*8.0/1024 as size_mb
[Code] ....
Following are the results:-
DB db_object_name cache_page_countsize_mb
TEST_DBNULL 428 3.34375
TEST_DBsysobjvalues 369 2.882812
TEST_DBsyscolpars 44 0.34375
TEST_DBsysssislog 38 0.296875
....
.....
Question- Why am I getting 428 pages for which there is no corresponding DB object? Why are so many pages present in sys.dm_os_buffer_descriptors but are missing from sys.allocation_units.
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Jul 16, 2015
What is better values for Buffer Cache Hot Ratio in SQL Server 2012. Is the values changed from 2008r2 to 2012?
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May 22, 2014
I have a virtual server (VMware ESX) with 64GB RAM running a single instance of SQL 2012 SP1. The max memory config is set to 59392 (58GB).
The Page Life Expectancy for this server has been averaging well under 10 mins for the last few days, according to our monitoring.
I have been checking the amount of data in the buffer cache periodically during the day with the below query, which seems to show that there is never more than about 10GB of data at any one time, frequently dropping below 5GB:
SELECT COUNT(*) AS BufferPages,
CONVERT(decimal(10, 2), COUNT(*) / 128.0) AS BufferMB
FROM sys.dm_os_buffer_descriptorsWhy would the amount of cached data be so low (and cause so much churn)?
I am aware that other things will require some of that memory (plan cache etc.) but with Max Mem of 58GB, I would expect there to be a much higher amount of actual cached data at any one time. I did the same checks on another VM with the same amount of RAM/Max Mem setting, and there was 50GB of data in the cache, with PLE measured in hours.
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Aug 17, 2015
I'm getting an alert which states that both my Buffer Cache Hit Ratio and PLE are low on one of my SQL Servers though I'm not sure how to correctly check this.
I ran:
SELECT object_name, counter_name, cntr_value
FROM sys.dm_os_performance_counters
WHERE [object_name] LIKE '%Buffer Manager%'
AND [counter_name] = 'Buffer cache hit ratio'
Which gives me the Buffer Cache Hit Ratio, cntr_Value of 9 though its constantly dipping between 3-3000 and is never steady and I'm unsure if this is normal.
I also ran:
SELECT object_name, counter_name, cntr_value
FROM sys.dm_os_performance_counters
WHERE [object_name] LIKE '%Buffer Manager%'
AND [counter_name] = 'Page life expectancy'
Which gives me the Page life expectancy of 209061.
If these values would cause concern and if this is a normal Buffer Cache Hit Ratio? It's constantly dropping from high or low from what I can see. These scripts were pulled from another forum and I'm assuming they're showing the correct values.
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Sep 12, 2014
Our server administrator forwarded some messages from SCOM that indicate:
SQL DB Engine 2012 Page Life Expectancy and Buffer Cache Hit Ratio is too low
When I logged into the offending server, I could not find anything in the SQL Log File that indicates this.
I was wondering how did SCOM identify this issue - where in SQL Server would this have been reported to SCOM?
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May 31, 2007
Is there a way to drop clean buffers at the database level instead of the server/instance level like the undocumented €śDBCC FLUSHPROCINDB (@dbid)€??
Is there a workaround for €śdbo€? to be able to flush procedure and data cache without being elevated to €śsysadmin€? server role?
PS: I am aware of the sp_recompile option that can be used to invalidate cached execution plans.
Thx.
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Sep 12, 2014
Is there anyway to clear the procedure cache of a single procedure?
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Dec 14, 2006
How do u clear Cache in SQL
if i run a query once it takes 10 seconds and if i run the same query again it takes 1 second because it is cached. So i want to know how i can clear it because i want do some benchmarking on a query that is in cache
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Apr 3, 2006
I am trying to improve the performance of a query. No matter how badit runs the first time, it runs really fast the second time.So how can I tell if I've done anything to improve the query if italways comes back quickly after the first run? I assume thequery/data/plan is in cache - how can I clean it out for my session?Thanks in advance for any help you can provide -
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Sep 30, 1999
Help, have recently upgraded from 6.5 to 7.0 and have come across a problem with performance. The problem appears to relate to the buffer cache being flushed, the buffer cache hit ratio drops from 98% to 0% in a matter of a second. It then very slowly grows, then is flushed again, then increase slowly upto 30%.
Does any one have any ideas as to what would flush the buffer cache?
Any comments would be much appreciated - cheers
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May 16, 2007
Hi,
My problem is that I cannot completely clean buffer cache on SQL Server 2005 version 9.00.2047.00 (probably SP1).
Right after I run DBCC DROPCLEANBUFFERS in the context of my database (this is development server, and so far I am only the one who is working with a particular database), I run a script that quetries sys.dm_os_buffer_descriptors view also from the context of my database to make sure that the buffer cache is really clean. However it shows large number of entries totalling 42 MB.
I ran both DBCC an the script in the past too, and it always showed nothing in the results, that means that buffers were really clean. The reason why I am running this is for benchmarking of existing and new application.
Does anybody have any idea, suggestions, how to troubleshoot this issue ? I already closed all connections to this database, but rebooting the server is not an option since other people are also working on it.
Thanks
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Jan 2, 2004
Does anyone know how to measure the buffer cache hit ratio? I have been reading a lot about it but can't find this measurement in Performance Monitor.
Thanks
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Jun 19, 2008
I am wondering if 100% buffer cache hit ratio is considered not good in general?
Are there instances that it is actually bad and can contribute to server performance degradation?
Any thoughts on the topic most welcome :)
--------------------
keeping it simple...
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Jul 23, 2005
This issue just happen recently. The buffer cache ratio went from > 90%to 50% and has slowly been climbing back up over 8 hours or so. Itscurrently @ 76%. Is this something I should take action on immediately?It seems to be coming back to normal...
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Sep 1, 2006
HiI have trouble with MSSQL2000 SP4 (without any hotfixes). During last twoweeks it start works anormally. After last optimalization (about few monthsago) it works good (fast, without blocks). Its buffer cache hit ratio wasabout 99.7-99.8. Last day it starts work slow, there was many blocks anddedlocks. There are no any queries, jobs and applications was added. Nowbuffer cache hit ratio oscilate about 95-98. I try update statistics andreindex some hard used tables, but there is no effect or effect is weryshort (after few hours problem return).Mayby somene know what it could be?Is it possible to estimate how each table (using DBCC SHOW_STATISTICS orDBCC SHOWCONTIG or others) how the table affect on total buffer cache hitratio?Marek---www.programowanieobiektowe.pl
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Jul 2, 2007
Hello,
Does the performance counter Buffer cache object refer to Data cache and procedure cache or just refers to Data cache???
I was of the opinion that Buffer cache means data cache and Plan cache means procedure cache. Can someone throw some light???
Regards
Jaideep
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Aug 3, 2015
I've a spatial (GIS) Data which is used frequently insertion, updation.
5 lakh records insertion in daily basis. when I trying to generate reports last 3 days or one weak, it takes 20-30 minute.
very disappointing while playing with clients. how to boostup and perform fast.
I think as so once we set query plan in buffer permanently then i would be faster than ever.
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Oct 20, 2011
How do i check the size of the datacache allocated from the buffer pool by sql server?
DMV or anything to show me the pool allocation sizes for the various pools in sql server i think i may be able to work from there.
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Dec 27, 2007
Im getting this error when trying to set up a cache dependency...are there any special permissions etc?From CS:SqlCacheDependency dep = new SqlCacheDependency("MySite-Cache", "Products");Cache.Insert("Products", de.GetAllProductsList(), dep); From connectionStrings.config:<add name="SiteDB" connectionString="Data Source=localhost,[port]SQLEXPRESS;Integrated Security=true;User Instance=true; AttachDBFileName=|DataDirectory|ASPNETDB.MDF" providerName="System.Data.SqlClient" />Also tried this using my machinename<add name="SiteDB" connectionString="Data
Source=<machinename>,[port]SQLEXPRESS;Integrated Security=true;User
Instance=true; AttachDBFileName=|DataDirectory|ASPNETDB.MDF"
providerName="System.Data.SqlClient" /> From web.config: <caching> <sqlCacheDependency enabled="true" pollTime="10000"> <databases> <add name="MySite-Cache" connectionStringName="SiteDB" pollTime="2000"/> </databases> </sqlCacheDependency> </caching> EDIT: So making progress I can't seem to get the table registered for cache dependency:The sample i have says"aspnet_regsql.exe -E -S .SqlExpress -d aspnetdb -t Customers -et"and the command line response is "Enabling the table for SQL cache dependency..An error has happened. Details of the exception:The table 'Customers' cannot be found in the database."Where does this "Customers" table come from? There is obviously not an application specific "Customers" table in aspnetdb I'm confused probably more by the example than anything....
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Jan 29, 2015
Looking at the recovery model on MSDN - was under the belief from it that if you set your database to use the simple recovery model, then when you preform a full back up it would truncate the transaction log file but this doesn't seem to be the case?We aren't looking to do a point in time recovery for this particular databse.
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Jan 4, 2015
I was able to do windows cluster successfully on vmware but after destroying it and I wanted to rebuild cluster on same nodes with same vmnode as DC.But Clustering kept failing.... and I had to rebuild entire vmnodes ,ISCSI SAN and Clustering from scratch...
How do I get over this problem.I want to manage cluster so it remains stable after failover or even after shut down of VMnodes????
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Sep 1, 2015
Last Sunday on our Primary server I saw some blocking and the First spid that blocked everything was waiting on LogBuffer wait. At that time the server was not running hot and our DB is on SSD's. There was no memory pressure(1 TB of memory on the server) It is strange why we should get LogBuffer wait when we are running on the fastest disks possible and there was not much action going on the DB.
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Jan 23, 2015
I am sure I have seen in the past in a monitoring tool that PLE drops off to 0 whenever we do a backup. I was doing some reading around this however and found something that said backups use a different portion of memory external to the buffer pool (minmax settings).
Is this correct and how can I tell how much memory will be required for a backup?
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Jan 13, 2015
All the recommendations I see from Microsoft docs is to limit the use of Query Notifications (QNs) to notifying connected clients when changes to mostly-static reference or configuration data occur, and to keep the number of overall query forms in play and connected clients to a minimum. Any way regarding a more integral use of QNs and Service Broker from a web app to notify n-web servers (farm) of an update to data that could be updated concurrently and quite frequently, or with a system where the technique is used extensively with lots of different query forms?
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Feb 25, 2015
On one server I'm having an issue with and it having such a small procedure cache.
Server has 60GB of RAM assigned to its min and max server memory settings, optimise for ad hoc workloads is disabled.
Procedure cache at the moment on the server is 2.41MB with only 6 objects in side all related to mssqlsystemresource database, I can see stuff dropping in for user databases, but as soon as the proc has finished the plan is removed from the cache.
Buffer cache is in the 17GB mark, free pages around the 42GB mark so around 60GB used with a bit in stolen pages, but no proc cache.
All other servers in the environment are reporting over 8GB of proc cache in use which is more healthy.
Using Spotlight to monitor all of this.
Whats wrong with this one server and it not keeping the plans in cache.
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Oct 5, 2006
Is there a simple method to clear all the tables in a db or to make a copy of the mdf file without the datas ?
I tried to use TRUNCATE TABLE but it doesn't work with foreign keys ?
Thanks.
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Apr 18, 2012
I encountered the following error while attempting to preview an RDL report I was developing in VS2010 using SSDT:"The size necessary to buffer the XML content exceeded the buffer quota"
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Oct 7, 2015
We have a set of reports with same header section in all the reports. So while developing a new report i used to copy that header section to the new report with same dataset names (without any change) , but while rendering the report it is throwing error " The size necessary to buffer the XML content exceeded the buffer quota".
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Apr 28, 2006
Hi
I have a master package that executes a series of sub packages run from a SQL Agent job. One of those sub packages has been stable for a week, running at least once per day, but it just failed despite having been run once already today with the same set of input data.
There were a series of errors showing in the event log for the Execute Package Task starting with "Buffer Type 15 had a size of 0 bytes.", then "The buffer manager failed to create a new buffer type.", then "The Data Flow task cannot register a buffer type. The type had 32 columns and was for execution tree 3.", then "The layout failed validation." and finally "Error 0xC0012050 while loading package file "C:[Package].dtsx". Package failed validation from the ExecutePackage task. The package cannot run.".
SQLIS.com reports the constant for the error code as DTS_E_REMOTEPACKAGEVALIDATION ( http://wiki.sqlis.com/default.aspx/SQLISWiki/0xC0012050.html ).
I then ran the package on my dev machine in BIDS and it worked fine, so I re-ran the job on the server and this time that package executed ok, but another one fell over but did not put anything in the event log.
Does any one have any idea what happened?
TIA . . . Ed
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Feb 12, 2015
What is the use of running DBCC FREESESSIONCACHE.
How frequently can we do this on all the databases.
What happens if we schedule to run it every 1min.
Are there any advantages/disadvantages of running this on all databases.
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Sep 30, 2006
I'm writing a web application that saves data to a Microsoft SQL database. As I build my application, I continually dirty my database with test data and refine my data schema. Is there a tool that can quickly remove all of the data from 4 of my 5 tables? Right now I'm using MS SQL Server Management Studio Express to open each table and manually deleting the rows of data and it's a pain in the ass. Playing around with the Management Express, I was able to generate a create SQL script (I'm afraid to test it though) that looks like it will rebuild my table. The problem is, one of my tables is a list (index?) of types...and I'd need that data saved
ebuilt each time...but I cannot figure out how to tell SQL that the rows in this table needs to be rebuilt (and is not really data per say).How do you guys "clear" or reset your database during development?-=STZ=-
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Jun 4, 2015
I am using SQL Server 2012 Express.
I am doing performance tuning of SP/Query in Dev-Test environment.
I found that SQL Server caches plan between successive executions.
So if I test/execute SP 10 times, after 1st or 2nd execution, SQL server will pull-up plan-info from CACHE...Not from SQL SERVER Or Database...
Means i am not getting correct answer...
I found this 2 commands:
DBCC FREEPROCCACHE
DBCC DROPCLEANBUFFERS
But they say that executing above command might interfere/bother other people executing other query/sp on this server.
They also say that: Freeing the plan cache causes, for example, a stored procedure to be recompiled instead of reused from the cache. This can cause a sudden, temporary decrease in query performance.
Part of query was using Dynamic-SQL executed with EXEC command.
I replaced that with SP_EXECUTESQL.
How can I start testing of each SP-run with Fresh/Blank CACHE ?
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