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！
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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
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.
*/
void
CheckpointWriteDelay(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;
}
}到此，关于“checkpoint中用于控制刷盘频率的函数是什么”的学习就结束了，希望能够解决大家的疑惑。理论与实践的搭配能更好的帮助大家学习，快去试试吧！若想继续学习更多相关知识，请继续关注创新互联网站，小编会继续努力为大家带来更多实用的文章！
