… Check for Table Cache Related Allocations There are cases when MySQL will allocate a lot of memory for table cache, especially if you… from OS you might not see “VSZ” going down. What you might see instead is flushing tables regularly or reducing table cache… and fixed. This is where your MySQL Support contract can be handy. Conclusion Understanding where MySQL can allocate memory can help us…
Post: What MySQL buffer cache hit rate should you target
June 29, 2006 By 5 Comments
…, how good was OS or SAN cache hit rate – something you would not see otherwise. The bad luck is – MySQL currently does not… bit in trouble) or “OS file reads”, “OS file writes” from SHOW INNODB STATUS for Innodb tables. In MySQL 5.0+ you can… it to the disk. In some configurations OS cache may take all of them. In some OS – ie Solaris you can use dtrace…
Post: The MySQL optimizer, the OS cache, and sequential versus random I/O
April 28, 2008 By 17 Comments
… Avg_row_length: 117 Data_length: 17217646764 Index_length: 11993816064 mysql> show table status like ‘dim1′\G *************************** 1. row *************************** Name: dim1… they stay in memory, in the OS cache. (They don’t get evicted from memory by the cache‘s LRU policy, because they… knowledge about the OS cache. This is why an expert is sometimes needed to provide the missing information. If the MySQL optimizer were…
Post: Query Profiling with MySQL: Bypassing caches
September 12, 2007 By 6 Comments
… simple – because SQL_NO_CACHE only bypasses query cache but it has no change on other caches, which are MySQL Caches – Innodb Buffer Pool and… is also table_cache both MySQL side and Internal Innodb one which can affect query execution speed. OS Caches Operation Systems typically cache file IO… clean Innodb Buffer Pool without restart. For OS Caches on Linux you can use drop caches control available in new Linux Kernels. You…
Post: Aligning IO on a hard disk RAID – the Benchmarks
June 9, 2011 By 11 Comments
… buffered in OS cache and so writes to files were serialized until they were fully overwritten and that way flushed from OS buffers… make sure caches were clean. OLTP benchmark As the goal was to compare performance with different IO alignment, not different MySQL configurations, I didn’t try out different MySQL versions or settings. Moreover, I have…
Post: What to tune in MySQL Server after installation
September 29, 2006 By 116 Comments
… of indexes, data size and workload – remember MyISAM uses OS cache to cache the data so you need to leave memory for it… Innodb buffer pool caches both data and index pages so you do not need to leave space for OS cache so values up… transactions even in case MySQL Server crashes. Value 2 only cause data loss with full OS crash. table_cache – Opening tables can be…
Post: Ultimate MySQL variable and status reference list
January 8, 2011 By 4 Comments
…MySQL…cache_hitsblogpercona.commanual Ssl_session_cache_missesblogpercona.commanual Ssl_session_cache_modeblogpercona.commanual Ssl_session_cache_overflowsblogpercona.commanual Ssl_session_cache_sizeblogpercona.commanual Ssl_session_cache…
Post: Cache Performance Comparison
August 9, 2006 By 73 Comments
…are: Cache Type Cache Gets/sec Array Cache 365000 APC Cache 98000 File Cache 27000 Memcached Cache (TCP/IP) 12200 MySQL Query Cache (TCP/IP) 9900 MySQL Query Cache (Unix… file cache is – there are actually two very different cases – when cached data set fits in memory well and so served from OS cache…
Post: Evaluating IO subsystem performance for MySQL Needs
March 5, 2008 By 23 Comments
… should expect from the system. What I usually look for MySQL is performance in random reads and random writes. Sequential reads… look at performance with O_DIRECT flag set to bypass OS cache. This may execute separate code path in kernel and so… followed by fsync regularly) , but it allows to easily bypass OS cache both for reads and for writes and so does not…
Post: fadvise - may be not what you expect
April 2, 2010 By 7 Comments
… call to avoid caching in OS cache. We recently made patch for tar, which supposes to create archive without polluting OS cache, as like in case with backup, you do not really expect any benefits from caching. However working on… of each block. Dirty, but it works, it only uses OS cache with one block size. You can get patch there lp…
