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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，丸趣 TV 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，请跟着丸趣 TV 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.
*/
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，请继续关注丸趣 TV 网站，丸趣 TV 小编会继续努力为大家带来更多实用的文章！
