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  • Innodb后台线程

    1.maste thread

    负责将缓冲池中的数据异步刷新到磁盘,保证数据的一致性。

    2.IO Thread
    负责IO请求的回调处理。
    1.0版本之前有4个IO Thread,负责write、read、insert buffer和log IO Thread
    1.0.x开始,read thread和write thread分别增加到4个,不再使用innodb_file_io_threads参数,而是使用innodb_read_io_threads和innodb_write_io_threads

    mysql> show variables like 'innodb_version'G
    *************************** 1. row ***************************
    Variable_name: innodb_version
            Value: 5.6.25
    1 row in set (0.00 sec)
    
    mysql> show variables like 'innodb_%io_threads'G
    *************************** 1. row ***************************
    Variable_name: innodb_read_io_threads
            Value: 4
    *************************** 2. row ***************************
    Variable_name: innodb_write_io_threads
            Value: 4
    2 rows in set (0.00 sec)
    
    mysql> show engine innodb statusG
    *************************** 1. row ***************************
      Type: InnoDB
      Name: 
    Status: 
    =====================================
    2015-12-20 21:53:50 7fcaccfe8700 INNODB MONITOR OUTPUT
    =====================================
    Per second averages calculated from the last 11 seconds
    -----------------
    BACKGROUND THREAD
    -----------------
    srv_master_thread loops: 93 srv_active, 0 srv_shutdown, 26243 srv_idle
    srv_master_thread log flush and writes: 26336
    ----------
    SEMAPHORES
    ----------
    OS WAIT ARRAY INFO: reservation count 393
    OS WAIT ARRAY INFO: signal count 347
    Mutex spin waits 297, rounds 8910, OS waits 281
    RW-shared spins 53, rounds 1590, OS waits 50
    RW-excl spins 13, rounds 1860, OS waits 57
    Spin rounds per wait: 30.00 mutex, 30.00 RW-shared, 143.08 RW-excl
    ------------
    TRANSACTIONS
    ------------
    Trx id counter 2545
    Purge done for trx's n:o < 2540 undo n:o < 0 state: running but idle
    History list length 22
    LIST OF TRANSACTIONS FOR EACH SESSION:
    ---TRANSACTION 0, not started
    MySQL thread id 5, OS thread handle 0x7fcaccfe8700, query id 491 localhost root init
    show engine innodb status
    --------
    FILE I/O
    --------
    I/O thread 0 state: waiting for i/o request (insert buffer thread)
    I/O thread 1 state: waiting for i/o request (log thread)
    I/O thread 2 state: waiting for i/o request (read thread)
    I/O thread 3 state: waiting for i/o request (read thread)
    I/O thread 4 state: waiting for i/o request (read thread)
    I/O thread 5 state: waiting for i/o request (read thread)
    I/O thread 6 state: waiting for i/o request (write thread)
    I/O thread 7 state: waiting for i/o request (write thread)
    I/O thread 8 state: waiting for i/o request (write thread)
    I/O thread 9 state: waiting for i/o request (write thread)
    Pending normal aio reads: 0 [0, 0, 0, 0] , aio writes: 0 [0, 0, 0, 0] ,
     ibuf aio reads: 0, log i/o's: 0, sync i/o's: 0
    Pending flushes (fsync) log: 0; buffer pool: 0
    915 OS file reads, 1496 OS file writes, 1089 OS fsyncs
    0.00 reads/s, 0 avg bytes/read, 0.00 writes/s, 0.00 fsyncs/s
    -------------------------------------
    INSERT BUFFER AND ADAPTIVE HASH INDEX
    -------------------------------------
    Ibuf: size 1, free list len 0, seg size 2, 0 merges
    merged operations:
     insert 0, delete mark 0, delete 0
    discarded operations:
     insert 0, delete mark 0, delete 0
    Hash table size 276671, node heap has 2 buffer(s)
    0.00 hash searches/s, 0.00 non-hash searches/s
    ---
    LOG
    ---
    Log sequence number 369664448
    Log flushed up to   369664448
    Pages flushed up to 369664448
    Last checkpoint at  369664448
    0 pending log writes, 0 pending chkp writes
    356 log i/o's done, 0.00 log i/o's/second
    ----------------------
    BUFFER POOL AND MEMORY
    ----------------------
    Total memory allocated 137363456; in additional pool allocated 0
    Dictionary memory allocated 96365
    Buffer pool size   8191
    Free buffers       53
    Database pages     8136
    Old database pages 2983
    Modified db pages  0
    Pending reads 0
    Pending writes: LRU 0, flush list 0, single page 0
    Pages made young 9747, not young 4864716
    0.00 youngs/s, 0.00 non-youngs/s
    Pages read 4212, created 12449, written 13322
    0.00 reads/s, 0.00 creates/s, 0.00 writes/s
    No buffer pool page gets since the last printout
    Pages read ahead 0.00/s, evicted without access 0.00/s, Random read ahead 0.00/s
    LRU len: 8136, unzip_LRU len: 0
    I/O sum[0]:cur[0], unzip sum[0]:cur[0]
    --------------
    ROW OPERATIONS
    --------------
    0 queries inside InnoDB, 0 queries in queue
    0 read views open inside InnoDB
    Main thread process no. 2345, id 140508950664960, state: sleeping
    Number of rows inserted 3919015, updated 0, deleted 0, read 8532141
    0.00 inserts/s, 0.00 updates/s, 0.00 deletes/s, 0.00 reads/s
    ----------------------------
    END OF INNODB MONITOR OUTPUT
    ============================
    
    1 row in set (0.00 sec)
    
    mysql> 
    

    3.purge thread
    事务提交后,purge thread线程回收已经分配并被使用的undo页。
    innodb 1.2开始,支持多个purge thread。
    purge thread离散地读取undo页。

    mysql> show variables like 'innodb_purge_threads';
    +----------------------+-------+
    | Variable_name        | Value |
    +----------------------+-------+
    | innodb_purge_threads | 1     |
    +----------------------+-------+
    1 row in set (0.00 sec)
    
    mysql> 
    

    4.page cleaner thread
    1.2.x版本中引入的。将之前版本中脏页的刷新操作都放入到单独的线程中来完成。减轻master thread的工作。

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  • 原文地址:https://www.cnblogs.com/abclife/p/5062008.html
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