os: centos 7.4
db: oracle 11.2.0.4

版本

# cat /etc/centos-release CentOS Linux release 7.4.1708 (Core) # # su - oracle Last login: Tue Jan 21 03:40:05 CST 2020 on pts/0 $ sqlplus / as sysdba;SQL*Plus: Release 11.2.0.4.0 Production on Mon Feb 3 10:29:09 2020Copyright (c) 1982, 2013, Oracle. All rights reserved.Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP, Data Mining and Real Application Testing optionsSQL> set lines 300; SQL> set pages 300; SQL> SQL> select * from v$version;BANNER -------------------------------------------------------------------------------- Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production PL/SQL Release 11.2.0.4.0 - Production CORE 11.2.0.4.0 Production TNS for Linux: Version 11.2.0.4.0 - Production NLSRTL Version 11.2.0.4.0 - ProductionSQL>

latch:cache buffers chains

當(dāng)一個(gè)數(shù)據(jù)塊讀入到sga中時(shí)，該塊的塊頭(buffer header)會(huì)放置在一個(gè)hash bucket的鏈表(hash chain)中。該內(nèi)存結(jié)構(gòu)由一系列cache buffers chains子latch保護(hù)（又名hash latch或者cbc latch）。對Buffer cache中的塊，要select或者update、insert,delete等，都得先獲得cache buffers chains子latch，以保證對chain的排他訪問。若在過程中發(fā)生爭用，就會(huì)等待latch:cache buffers chains事件。

在以下場景容易出現(xiàn)該事件

熱塊( hot block )

--直接找出熱點(diǎn)塊 SELECT OBJECT_NAME, SUBOBJECT_NAMEFROM DBA_OBJECTSWHERE DATA_OBJECT_ID IN(SELECT DATA_OBJECT_IDFROM (SELECT OBJ DATA_OBJECT_ID, FILE#, DBABLK, CLASS, STATE, TCHFROM X$BHWHERE HLADDR IN (SELECT ADDRFROM (SELECT ADDRFROM V$LATCH_CHILDRENORDER BY (GETS + MISSES + SLEEPS) DESC)WHERE ROWNUM < 10)ORDER BY TCH DESC)WHERE ROWNUM < 10);

低效率的SQL語句(主要體現(xiàn)在邏輯讀過高，個(gè)人感覺也體現(xiàn)在熱塊上)

可以通過將普通表調(diào)整成分區(qū)表，普通索引調(diào)整為分區(qū)索引的方法去嘗試解決。

buffer busy waits

當(dāng)一個(gè)會(huì)話獲取數(shù) buffer cache 中一個(gè)數(shù)據(jù)塊時(shí)，但是 buffer 處于繁忙狀態(tài)，無法獲取，

主要原因?yàn)?/p>

其它會(huì)話正在將數(shù)據(jù)塊讀入 buffer

其它會(huì)話以排它模式持有buffer

可以將普通表做成分區(qū)表,將定期將索引刪除并重建,調(diào)整表和索引pctfree參數(shù)

參考：

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