Category等待事件

ORACLE11.2.0.3数据库alter table drop column慢原因分析

中午某生产数据库发布补丁,开发人员反应有语句阻塞,无法执行下面语句
alter table pyramid.pd_loanProduct drop column customerType;
这是一个只有4行的小表

我建个测试表尝试了一下,果然很慢
create table pyramid.test_alter2(id number,name varchar2(10))  ;
alter table pyramid.test_alter2 drop column name;

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WAITEVENT: “log file sync” Reference Note (文档 ID 34592.1)

WAITEVENT: “log file sync” Reference Note (文档 ID 34592.1)

Versions:7.0 – 11.1 Documentation: 11g 10g
When a user session(foreground process) COMMITs (or rolls back), the session’s redo information needs to be flushed to the redo logfile. The user session will post the LGWR to write all redo required from the log buffer to the redo log file. When the LGWR has finished it will post the user session. The user session waits on this wait event while waiting for LGWR to post it back to confirm all redo changes are safely on disk.

This may be described further as the time user session/foreground process spends waiting for redo to be flushed to make the commit durable. Therefore, we may think of these waits as commit latency from the foreground process (or commit client generally).

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