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table cache hit rate

Discussion in 'Server Configuration and Hosting' started by MattW, Feb 7, 2013.

  1. MattW

    MattW Well-Known Member

    I've recently been running MySQL tuner, and it keeps reporting that my table cache hit rate is at 0%

    It's only just started reporting this, as it used to report:

    1K open / 14K opened after 20 days of uptime

    It's now reporting a LOT more tables being opened, even after just 15 hours

    Any recommendations on these settings?

  2. MattW

    MattW Well-Known Member

    and the output from tuningprimer.sh regarding the tables

    Current table_open_cache = 20000 tables
    Current table_definition_cache = 4096 tables
    You have a total of 1241 tables
    You have 2171 open tables.
    The table_cache value seems to be fine

    Current max_heap_table_size = 32 M
    Current tmp_table_size = 32 M
    Of 48940 temp tables, 17% were created on disk
    Created disk tmp tables ratio seems fine

    Current read_buffer_size = 128 K
    Current table scan ratio = 64 : 1
    read_buffer_size seems to be fine
  3. Mouth

    Mouth Well-Known Member

    What's your table_open_cache setting?

    I would love to know what app that is you are using for the iPad? Thanks.
  4. MattW

    MattW Well-Known Member

  5. MattW

    MattW Well-Known Member

    I changed a few things round yesterday and put a few variables back to how they were a few months back, and it's looking at lot better now

     >>  MySQLTuner 1.2.0 - Major Hayden <major@mhtx.net>
    >>  Bug reports, feature requests, and downloads at http://mysqltuner.com/
    >>  Run with '--help' for additional options and output filtering
    -------- General Statistics --------------------------------------------------
    [--] Skipped version check for MySQLTuner script
    [OK] Currently running supported MySQL version 5.5.29-29.4-log
    [OK] Operating on 64-bit architecture
    -------- Storage Engine Statistics -------------------------------------------
    [--] Status: +Archive -BDB -Federated +InnoDB -ISAM -NDBCluster
    [--] Data in MyISAM tables: 89M (Tables: 524)
    [--] Data in InnoDB tables: 659M (Tables: 669)
    [--] Data in PERFORMANCE_SCHEMA tables: 0B (Tables: 17)
    [--] Data in MEMORY tables: 372K (Tables: 7)
    [!!] Total fragmented tables: 83
    -------- Security Recommendations  -------------------------------------------
    [OK] All database users have passwords assigned
    -------- Performance Metrics -------------------------------------------------
    [--] Up for: 13h 6m 45s (602K q [12.770 qps], 44K conn, TX: 2B, RX: 95M)
    [--] Reads / Writes: 74% / 26%
    [--] Total buffers: 1.3G global + 2.8M per thread (80 max threads)
    [OK] Maximum possible memory usage: 1.6G (38% of installed RAM)
    [OK] Slow queries: 0% (8/602K)
    [OK] Highest usage of available connections: 11% (9/80)
    [OK] Key buffer size / total MyISAM indexes: 128.0M/82.5M
    [OK] Key buffer hit rate: 99.8% (2M cached / 4K reads)
    [OK] Query cache efficiency: 64.0% (232K cached / 363K selects)
    [OK] Query cache prunes per day: 0
    [OK] Sorts requiring temporary tables: 0% (0 temp sorts / 16K sorts)
    [!!] Joins performed without indexes: 230
    [OK] Temporary tables created on disk: 19% (3K on disk / 15K total)
    [OK] Thread cache hit rate: 99% (9 created / 44K connections)
    [OK] Table cache hit rate: 91% (1K open / 1K opened)
    [OK] Open file limit used: 2% (1K/65K)
    [OK] Table locks acquired immediately: 99% (236K immediate / 236K locks)
    [OK] InnoDB data size / buffer pool: 659.8M/1.0G
    -------- Recommendations -----------------------------------------------------
    General recommendations:
        Run OPTIMIZE TABLE to defragment tables for better performance
        MySQL started within last 24 hours - recommendations may be inaccurate
        Adjust your join queries to always utilize indexes
    Variables to adjust:
        join_buffer_size (> 128.0K, or always use indexes with joins)
    CyclingTribe likes this.
  6. p4guru

    p4guru Well-Known Member

    FYI mysqltuner values and recommendations are just based on a preconceived and not entirely accurate formula

    in relation to mysqltuner.pl original version, table cache hit rate recommendation is triggered when the ratio of tables open to tables opened is less <20:1

    This ratio doesn't really mean much, as tables opened is incremented when you hit table_open_cache limit but also is increased with temp table creation. I suspect raising your max tmp/heap sizes from 32M to 64M did more good for this. Not going into a long explanation, but if you look at tuningprimer.sh it reports tables cached is fine.

    Just remember tuningprimer.sh and mysqltuner.pl only report guidelines and you need to look at the actual numbers/stats themselves to determine if you're running optimally and not just rely on preconceived formulas and ratios ;)
    MattW likes this.
  7. emc2

    emc2 Active Member

    Glad I found this thread as I've also had this issue. I'll have to look at increasing my tmp/heap sizes as well.
    MattW likes this.
  8. p4guru

    p4guru Well-Known Member

    Cause and solution might not be entirely the same - as I said above, depends on specific values for various status variables.

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