GaussDB T 基础入门：等待事件 的分类和数量等
【摘要】 等待事件是会话等待某个系统行为发生的事件。等待事件可能由许多因素引起，从磁盘上的慢速读/写，到架构引起的锁定情况，到各种系统资源争用。
等待事件是会话等待某个系统行为发生的事件。等待事件可能由许多因素引起，从磁盘上的慢速读/写，到架构引起的锁定情况，到各种系统资源争用。
等待是系统级或会话级的。会话级等待事件是影响数据库中单个用户活动的事件。系统级等待事件会影响整个数据库系统。用户可通过对等待事件进行分析来定位系统性能问题。
GaussDB T 提供了总共7大类等待事件：Idle、Concurrency、Other、Commit、Application、User I/O、Configuration，总共31种等待事件。
可通过DV_SESSION_EVENTS、DV_SESSION_WAITS查询会话级等待事件的统计信息，可通过DV_SYS_EVENTS查询系统级等待事件的统计信息。
Name Null? Type ----------------------------------- -------- ------------------------------------ EVENT# NOT NULL BINARY_INTEGER EVENT NOT NULL VARCHAR(64 BYTE) P1 NOT NULL VARCHAR(64 BYTE) WAIT_CLASS NOT NULL VARCHAR(64 BYTE) TOTAL_WAITS NOT NULL BINARY_BIGINT TIME_WAITED NOT NULL BINARY_BIGINT TIME_WAITED_MIRCO NOT NULL BINARY_BIGINT AVERAGE_WAIT NOT NULL BINARY_DOUBLE AVERAGE_WAIT_MIRCO NOT NULL BINARY_BIGINT SQL> select count(*) from DV_SYS_EVENTS; COUNT(*) -------------------- 31 1 rows fetched. SQL> select event ,wait_class from dv_sys_events; EVENT WAIT_CLASS ---------------------------------------------------------------- ---------------------------------------------------------------- idle wait Idle message from client Idle message to client Idle latch: large pool Concurrency latch: sql pool Concurrency latch: lock pool Concurrency latch: dictionary pool Concurrency latch: data buffer pool Concurrency latch: cache buffers chains Concurrency cursor: mutex Other library : mutex Other log file sync Commit buffer busy waits Concurrency enq: TX row lock contention Application enq: TX alloc itl entry Concurrency enq: TX index contention Application enq: TX table lock S Application enq: TX table lock X Application enq: TX read wait Application db file scattered read User/IO db file sequential read User/IO log file switch(checkpoint incomplete) Configuration log file switch(archiving needed) Configuration read by other session Concurrency attached to agent Idle heap find map Concurrency heap extend segment Concurrency resmgr: io quantum User/IO direct path read temp User/IO direct path write temp User/IO advisory lock wait time Concurrency 31 rows fetched. SQL>
转自墨天轮
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