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Oracle IO on linux: log writer IO and wait events

This post is about log writer (lgwr) IO.
It’s good to point out the environment on which I do my testing:
Linux X64 OL6u3, Oracle 11.2.0.3 (no BP), Clusterware 11.2.0.3, ASM, all database files in ASM.

In order to look at what the logwriter is doing, a 10046 trace of the lgwr at level 8 gives an overview.
A way of doing so is using oradebug. Be very careful about using oradebug on production environments, it can/may cause the instance to crash.

This is how I did it:

SYS@v11203 AS SYSDBA> oradebug setospid 2491
Oracle pid: 11, Unix process pid: 2491, image: oracle@ol63-oracle.local (LGWR)
SYS@v11203 AS SYSDBA> oradebug unlimit
Statement processed.
SYS@v11203 AS SYSDBA> oradebug event 10046 trace name context forever, level 8
Statement processed.

Of course 2491 is the Linux process id of the log writer, as is visible with “image”.