View mysql query cache contents
I have a large database application that uses mysqls query cache ability. I'd like to inspect the contents of the query cache to identify entries that should not get cached (e.g. by using SELECT SQL_NO_CACHE...) because I want to optimize my application.
Is there a way to get a list of cached entries from the query cache?
-- Edit: additional info as suggested by Rick ---
1) RAM size is 16GB
2) show variables;
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version 5.1.56-log
version_comment Gentoo Linux mysql-5.1.56
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3) show global status;
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Answer
Observations:
Version: 5.1.56-log
16 GB of RAM
Uptime = 53d 21:20:56
You are not running on Windows.
Running 64-bit version
It appears that you are running both MyISAM and InnoDB.
The More Important Issues
key_buffer_size = 1500M
innodb_buffer_pool_size = 2000M
join_buffer_size = 1M -- This may be the most important
tmp_table_size = 256M -- Also important
query_cache_size = 50M -- as already mentioned
Use slowlog to find tmp tables spilling to disk
Three settings were especially high and could lead to paging/swapping. MySQL performance suffers terribly when paged/swapped. It is better to lower settings than to have that happen.
Details and Minor Issues
( innodb_buffer_pool_size / _ram ) = 1024M / 16384M = 6.2% -- % of RAM used for InnoDB buffer_pool
( Innodb_pages_written / Innodb_buffer_pool_write_requests ) = 29,673,396 / 196667000 = 15.1% -- Write requests that had to hit disk -- Check innodb_buffer_pool_size
( Innodb_buffer_pool_read_ahead_evicted / Innodb_buffer_pool_read_ahead ) = 4,691,916 / 30144135 = 15.6% -- Utility of read_ahead. -- Turn off read-ahead
( Innodb_os_log_written / (Uptime / 3600) / innodb_log_files_in_group / innodb_log_file_size ) = 34,746,359,296 / (4656056 / 3600) / 2 / 256M = 0.05 -- Ratio
( Uptime / 60 * innodb_log_file_size / Innodb_os_log_written ) = 4,656,056 / 60 * 256M / 34746359296 = 599 -- Minutes between InnoDB log rotations Beginning with 5.6.8, this can be changed dynamically; be sure to also change my.cnf. -- (The recommendation of 60 minutes between rotations is somewhat arbitrary.)
( table_open_cache ) = 4,096 -- Number of table descriptors to cache -- Several hundred is usually good.
( innodb_stats_on_metadata ) = ON -- Re-analyze table when touching stats. -- ON is likely to slow down certain SHOWs and information_schema accesses.
( join_buffer_size ) = 2,147,483,648 = 2048MB -- 0-N per thread. May speed up JOINs (better to fix queries/indexes) (all engines) Used for index scan, range index scan, full table scan, each full JOIN, etc. -- Use the default.
( join_buffer_size / _ram ) = 2,147,483,648 / 16384M = 12.5% -- 0-N per thread. May speed up JOINs (better to fix queries/indexes) (all engines) Used for index scan, range index scan, full table scan, each full JOIN, etc. -- Decrease join_buffer_size to avoid memory pressure. Suggest less than 1% of RAM.
( min( tmp_table_size, max_heap_table_size ) / _ram ) = min( 2147483648, 256M ) / 16384M = 1.6% -- Percent of RAM to allocate when needing MEMORY table (per table), or temp table inside a SELECT (per temp table per some SELECTs). Too high may lead to swapping. -- Decrease tmp_table_size and max_heap_table_size to, say, 1% of ram.
( (key_buffer_size - 1.2 * Key_blocks_used * 1024) / _ram ) = (4294967296 - 1.2 * 864035 * 1024) / 16384M = 18.8% -- Percent of RAM wasted in key_buffer. -- Decrease key_buffer_size
( Key_blocks_used * 1024 / key_buffer_size ) = 864,035 * 1024 / 4294967296 = 20.6% -- Percent of key_buffer used . High-water-mark. -- Lower key_buffer_size to avoid unnecessary memory usage.
( Key_writes / Key_write_requests ) = 7,764,232 / 105012022 = 7.4% -- key_buffer effectiveness for writes
( query_cache_size ) = 1024M -- Size of QC -- Too small = not of much use. Too large = too much overhead. Recommend either 0 or no more than 50M.
( Created_tmp_disk_tables / (Created_tmp_disk_tables + Created_tmp_tables) ) = 2,151,917 / (2151917 + 3928177) = 35.4% -- Percent of temp tables that spilled to disk
( tmp_table_size ) = 2,147,483,648 = 2048MB -- Limit on size of MEMORY temp tables used to support a SELECT -- Decrease tmp_table_size to avoid running out of RAM. Perhaps no more than 64M.
( back_log / max_connections ) = 50 / 120 = 41.7%
( max_connect_errors ) = 100,000 -- A small protection against hackers. -- Perhaps no more than 200.