checkpoint中用于控制刷盘频率的函数是什么

这篇文章主要介绍"checkpoint中用于控制刷盘频率的函数是什么"，在日常操作中，相信很多人在checkpoint中用于控制刷盘频率的函数是什么问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答"checkpoint中用于控制刷盘频率的函数是什么"的疑惑有所帮助！接下来，请跟着小编一起来学习吧！

一、数据结构

宏定义
checkpoints request flag bits
checkpoints request flag bits,检查点请求标记位定义.

/* * OR-able request flag bits for checkpoints.  The "cause" bits are used only * for logging purposes.  Note: the flags must be defined so that it's * sensible to OR together request flags arising from different requestors. *//* These directly affect the behavior of CreateCheckPoint and subsidiaries */#define CHECKPOINT_IS_SHUTDOWN  0x0001  /* Checkpoint is for shutdown */#define CHECKPOINT_END_OF_RECOVERY  0x0002  /* Like shutdown checkpoint, but                       * issued at end of WAL recovery */#define CHECKPOINT_IMMEDIATE  0x0004  /* Do it without delays */#define CHECKPOINT_FORCE    0x0008  /* Force even if no activity */#define CHECKPOINT_FLUSH_ALL  0x0010  /* Flush all pages, including those                     * belonging to unlogged tables *//* These are important to RequestCheckpoint */#define CHECKPOINT_WAIT     0x0020  /* Wait for completion */#define CHECKPOINT_REQUESTED  0x0040  /* Checkpoint request has been made *//* These indicate the cause of a checkpoint request */#define CHECKPOINT_CAUSE_XLOG 0x0080  /* XLOG consumption */#define CHECKPOINT_CAUSE_TIME 0x0100  /* Elapsed time */

WRITES_PER_ABSORB

/* interval for calling AbsorbSyncRequests in CheckpointWriteDelay *///调用AbsorbSyncRequests的间隔,默认值为1000#define WRITES_PER_ABSORB   1000

二、源码解读

CheckpointWriteDelay
CheckpointWriteDelay,控制checkpoint的频率,逻辑不复杂,判断checkpoint flags非CHECKPOINT_IMMEDIATE/非shutdown_requested/非CHECKPOINT_IMMEDIATE并且checkpoint处于调度中,如满足上述条件,则调用AbsorbSyncRequests处理sync,休眠100ms;不如满足上述条件,则absorb_counter计数器减一,如计数器≤0,则调用AbsorbSyncRequests处理sync.

/* * CheckpointWriteDelay -- control rate of checkpoint * 控制checkpoint的频率 * * This function is called after each page write performed by BufferSync(). * It is responsible for throttling BufferSync()'s write rate to hit * checkpoint_completion_target. * * The checkpoint request flags should be passed in; currently the only one * examined is CHECKPOINT_IMMEDIATE, which disables delays between writes. * * 'progress' is an estimate of how much of the work has been done, as a * fraction between 0.0 meaning none, and 1.0 meaning all done. */voidCheckpointWriteDelay(int flags, double progress){  static int  absorb_counter = WRITES_PER_ABSORB;  /* Do nothing if checkpoint is being executed by non-checkpointer process */  if (!AmCheckpointerProcess())    return;  /*   * Perform the usual duties and take a nap, unless we're behind schedule,   * in which case we just try to catch up as quickly as possible.   */  if (!(flags & CHECKPOINT_IMMEDIATE) &&//非CHECKPOINT_IMMEDIATE    !shutdown_requested &&//非关闭请求    !ImmediateCheckpointRequested() &&//非CHECKPOINT_IMMEDIATE    IsCheckpointOnSchedule(progress))//处于checkpoint调度中  {    if (got_SIGHUP)    {      got_SIGHUP = false;      ProcessConfigFile(PGC_SIGHUP);      /* update shmem copies of config variables */      UpdateSharedMemoryConfig();    }    //Absorb吸收(处理)同步请求    AbsorbSyncRequests();    //重置为WRITES_PER_ABSORB(1000)    absorb_counter = WRITES_PER_ABSORB;    //检查归档是否超时    CheckArchiveTimeout();    /*     * Report interim activity statistics to the stats collector.     */    //统计信息    pgstat_send_bgwriter();    /*     * This sleep used to be connected to bgwriter_delay, typically 200ms.     * That resulted in more frequent wakeups if not much work to do.     * Checkpointer and bgwriter are no longer related so take the Big     * Sleep.     */    //休眠100ms    pg_usleep(100000L);  }  else if (--absorb_counter <= 0)//Absorb计数器减一  {    //如计数器小于等于0    /*     * Absorb pending fsync requests after each WRITES_PER_ABSORB write     * operations even when we don't sleep, to prevent overflow of the     * fsync request queue.     */    //Absorb同步请求    AbsorbSyncRequests();    //重置计数器    absorb_counter = WRITES_PER_ABSORB;  }}

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