共計 3866 個字符，預計需要花費 10 分鐘才能閱讀完成。
這篇文章主要介紹“checkpoint 中用于控制刷盤頻率的函數是什么”，在日常操作中，相信很多人在 checkpoint 中用于控制刷盤頻率的函數是什么問題上存在疑惑，丸趣 TV 小編查閱了各式資料，整理出簡單好用的操作方法，希望對大家解答”checkpoint 中用于控制刷盤頻率的函數是什么”的疑惑有所幫助！接下來，請跟著丸趣 TV 小編一起來學習吧！
一、數據結構
宏定義
checkpoints request flag bits
checkpoints request flag bits, 檢查點請求標記位定義.
/*
* 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 */
// 調用 AbsorbSyncRequests 的間隔, 默認值為 1000
#define WRITES_PER_ABSORB 1000二、源碼解讀
CheckpointWriteDelay
CheckpointWriteDelay, 控制 checkpoint 的頻率, 邏輯不復雜, 判斷 checkpoint flags 非 CHECKPOINT_IMMEDIATE/ 非 shutdown_requested/ 非 CHECKPOINT_IMMEDIATE 并且 checkpoint 處于調度中, 如滿足上述條件, 則調用 AbsorbSyncRequests 處理 sync, 休眠 100ms; 不如滿足上述條件, 則 absorb_counter 計數器減一, 如計數器≤0, 則調用 AbsorbSyncRequests 處理 sync.
/*
* CheckpointWriteDelay -- control rate of checkpoint
* 控制 checkpoint 的頻率
*
* 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 // 非關閉請求
!ImmediateCheckpointRequested() // 非 CHECKPOINT_IMMEDIATE
IsCheckpointOnSchedule(progress))// 處于 checkpoint 調度中
{ if (got_SIGHUP)
{
got_SIGHUP = false;
ProcessConfigFile(PGC_SIGHUP);
/* update shmem copies of config variables */
UpdateSharedMemoryConfig();
}
//Absorb 吸收 (處理) 同步請求
AbsorbSyncRequests();
// 重置為 WRITES_PER_ABSORB(1000)
absorb_counter = WRITES_PER_ABSORB;
// 檢查歸檔是否超時
CheckArchiveTimeout();
/*
* Report interim activity statistics to the stats collector.
*/
// 統計信息
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 計數器減一
{
// 如計數器小于等于 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 同步請求
AbsorbSyncRequests();
// 重置計數器
absorb_counter = WRITES_PER_ABSORB;
}
}到此，關于“checkpoint 中用于控制刷盤頻率的函數是什么”的學習就結束了，希望能夠解決大家的疑惑。理論與實踐的搭配能更好的幫助大家學習，快去試試吧！若想繼續學習更多相關知識，請繼續關注丸趣 TV 網站，丸趣 TV 小編會繼續努力為大家帶來更多實用的文章！
