29

The Buffer pool size 393215 This is in pages not bytes. To see the Buffer Pool size in GB run this: SELECT FORMAT(BufferPoolPages*PageSize/POWER(1024,3),2) BufferPoolDataGB FROM (SELECT variable_value BufferPoolPages FROM information_schema.global_status WHERE variable_name = 'Innodb_buffer_pool_pages_total') A, (SELECT variable_value PageSize FROM ...


19

'I am trying to determine if memory pressure is an issue to some of my problem.' very useful script: https://github.com/ktaranov/sqlserver-kit/blob/master/Scripts/SQLServer_Memory_Information.sql you see verbose memory utilization: https://www.sqlskills.com/blogs/glenn/sql-server-diagnostic-information-queries-for-november-2017/ SQL Server 2017 Diagnostic ...


18

Buffer pool hit rate is 1000 / 1000 This is the only really meaningful value in the situation that you are in... and that situation is that you are lucky enough to have a buffer pool with a perfect 100% hit rate. Don't over-analyze the rest of it, because there is nothing you need to change, unless the server OS is low on memory, causing swapping. The ...


14

Can someone direct to a good/proper explanation. I would start by saying Task Manager is not a correct place to gauge SQL Server memory consumption, it will not tell you correct value when SQL Server service account has Locked Pages in Memory(LPIM) privilege. This is because normally task manager tracks Process Private bytes which is pageable memory and ...


13

Pages are read into memory as required, if there is no free memory available, the oldest unmodified page is replaced with the incoming page. This means if you execute a query that requires more data than can fit in memory, many pages will live a very short life in memory, resulting in a lot of I/O. You can see this effect by looking at the "Page Life ...


10

This is a complicated topic, much of which is covered in this Microsoft Docs article. To answer a couple of points: Are (disk-based, so no Hekaton) tables persisted in memory for longer than the lifespan of the query that is reading data from them? Sort of. Entire tables aren't necessarily persisted in memory. Individual pages from a table or index ...


9

Your buffer pool is only 13GB and your databases are 383 GB and 378 GB which you have classified as being OLTP - small transactions running too frequently. The above situation, if I have to imagine is like below : (source : Google Photos) You have to understand how SQL Server stores information : SQL Server stores information in memory in a structure ...


9

We have been monitoring some SQLServer: Memory Manager's metrics, and noticed that after DBCC CheckDB job, metric Database Cache Memory (KB) drops down significantly. If to be exact, it dropped from 140 GB cached DB memory to 60 GB This is correct, you can clearly see this behaviour when this example DBCC CHECKDB command completes at 21h45 Why ...


8

No, there is no way to restore the buffer pool. Some will suggest pre-filling it by selecting all rows from all tables, but that is just silly given how rare it is for systems to use all rows from all tables (among other reasons that it wouldn't do what such an action is perceived to do). I'm not even sure that it makes sense conceptually that this should ...


7

When I go back to MySQL 5.5, I would think about this same thing. What I learned over those years was the following: If the Buffer Pool was bigger than half the installed RAM and innodb_buffer_pool_instances was 1 (default for 5.5), the threat of swapping was always imminent. I discussed this before : Is there a rule of thumb regarding the size and number ...


7

There is very little to debug here - you need to add memory, logically split your database across multiple VMs, or understand that the shuffling you have to do with limited memory will lead to performance issues and volatile PLE. Trying to fit 800 GB of data into 13 GB of memory is like trying to stow away in a backpack.


7

A query always reads data from memory (a logical read). Your example query scanning the TestLarge table touched 159,185 8KB memory pages during its execution. During execution, SQL Server does two things. 1. It reads data from the pages that belong to the table. If the required page is already in memory, a logical read is recorded. If the required page is ...


6

I'll disagree with the assessment that "you are lucky enough to have a buffer pool with a perfect 100% hit rate" At the top of the output (which is chopped off), is a line something like: Per second averages calculated from the last 16 seconds This says to me that no reads happened in the last 16 seconds, thereby (artificially) giving you a perfect '1000/...


6

Number of buffer pool instances should be increased to avoid buffer pool mutex contention. With buffer pool size 8GB I doubt you'll ever see the buffer pool mutex contention. UPDATE 0: I mention 8Gb buffer pool in the answer while in the original question the total memory was 8GB. Sure, the buffer pool must be less than 8GB. 4GB sounds like a good start ...


6

Assuming, you have a 7200 rpm HDD, if you perform random reads and expect the data to be loaded whenever it is required by the application, it will slow down the whole process. Random reads are way slower than sequential reads in case of HDD. So, rather the records must be loaded in sequential access. It may take a while under a regular workload to store ...


5

Q: I have a production data base that is experiencing wildly fluctuating Page Life Expectancy (PLE) issues. (It crashes to zero at random times.) Let me ask you what is output of Select @@Version. What is SP and CU level to which your SQL Server is patched. The reason I am asking this is because there was bug in SQl Server 2012 which forced PLE to ...


5

It's almost certainly going to be full backups or indexing. The queries won't show up as a bunch of memory allocated but rather as intensive disk IO. If you are tracking those counters then have a look. Some other easy ways to confirm that these are the cause of that disk IO: Looking at agent job schedules. If it wasn't checkdb, or indexing, then apps often ...


5

I can't speak to what exactly your query would do in this scenario but SQL Server has several options depending on how much is needed. Data can "spill" to TempDB, this would be using your disk Old pages can be pushed out of your buffer cache SQL Server can load some pages to buffer cache, use them, then rotate new pages in The best way to find out what ...


4

You may need to tune your writes for InnoDB and possibly your ext4 volume ASPECT #1 I noticed you have innodb_write_io_threads set to 4 (default value). You need to increase that so dirty pages can get flushed to their respective .ibd files more robustly. Please set it 16. ASPECT #2 That pause to perform write might be do to ext4. Why ? You have ...


4

This was a group effort and my role is mostly as a curator. There are many reasons why you could be seeing the results you're seeing. Zane offered a few potential causes when he commented: Is the VM overcomitted on memory? Are other activities peaking during this time and therefore windows is having to take memory back from SQL server? Does this happen ...


4

First, check the plan cache with queries that hit sys.dm_exec_query_stats. My favorite is the open source sp_BlitzCache (disclaimer: I'm one of the coauthors). Queries could be running outside of your control, like monitoring systems. I've seen third party tools that do things like check table fragmentation. Next, not everything stays in the plan cache. ...


4

SHOW GLOBAL STATUS LIKE 'Innodb_buffer_pool_pages_free' and SHOW GLOBAL STATUS LIKE 'Innodb_buffer_pool_pages_total' will enable you to derive this percentage. Keep in mind a page_free of 0 isn't fatal or even necessary bad - it just means every once in a while a read will come from disk or page cache. Its the rate at this occurs that is more important to ...


4

db2stop/db2start is not required to make a newly created bufferpool useable, but in most cases you must deactivate and reactivate the database for the tablespaces to be able to use the new bufferpool. This is because, even if the IMMEDIATE option is specified or implicitly assumed If there is not enough reserved space in the database shared memory to ...


3

After a long experimentation, I've found the problem to be the infamous swap insanity. The problem has been fixed by using the innodb-numa-interleave option.


3

If you are using SQL Server, write operations pull pages into memory if they need to be modified and write the changes to the page in memory as well as the transaction log. At given intervals those changes, and other changes made to adjacent pages since the last disk write operation occurred, are written to disk. This allows the server to make more logical ...


3

You can't "estimate" the size of a buffer pool, because the answer is, "it depends". Try using the AUTOCONFIGURE command to get started, and enable STMM. Together these will go a long way towards getting your database running more efficiently. I would also recommend you spend some time reading about DB2 Performance Tuning. There is a ton of information ...


3

From what you gave me thus far The CPU has the illustrious task of accessing all 32GB RAM. InnoDB's Buffer Pool is 8GB (524288 * 16384) 524288 (Innodb_buffer_pool_pages_total) 16384 (Innodb_page_size)) InnoDB Architecture CONJECTURE #1 Since InnoDB allocates its buffer pool contiguously, one could only imagine if there is any form of fragmentation of ...


3

Part 1 of the answer to your question is no, you can't selectively tell MySQL what not to store in the InnoDB buffer pool. It's an integral part of how InnoDB manipulates table data. Part 2 is that you don't really want to or need to, because it's smart enough to work out what should stay there if the pool is not large enough to retain your entire data set....


3

According to MySQL 5.7 Reference Manual - The InnoDB Buffer Pool InnoDB manages the buffer pool as a list, using a variation of the least recently used (LRU) algorithm. When room is needed to add a new page to the pool, InnoDB evicts the least recently used page and adds the new page to the middle of the list. This “midpoint insertion strategy” treats the ...


3

A buffer is an 8 KB page in memory, the same size as a data or index page you can consider buffer as a frame which holds data and index pages when they are brought from disk to memory. SQL Server buffer manager manages the task of reading data pages into buffer pool and also writing it to disk. It is a reserved memory store for SQL Server and by default if ...


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