Posted by If you are on any version of the database past 10.2.0.4, then savvy DBA’s may have noticed the following message popping up occasionally in their trace files
Warning: log write time 540ms, size 444KB
In itself, that is quite a nice little addition – an informational message letting you know that perhaps your log writer performance is worth closer investigation. MOS Note 601316.1 talks a little more about this message.
So let’s say you have seen this warning, and you are interested in picking up more information. Well… you could start scanning trace files from time to time, and parsing out the content etc, or do some analysis perhaps using Active Session History, but given that these warnings are (by default) triggered at above 500ms, there’s a chance you might miss them via ASH.
In 12c, this has become a lot simpler – because it looks like the same data is now exposed via a view, v$lgwrio_outlier
sql> select function_name,io_size,file_name,io_latency
2 from V$LGWRIO_OUTLIER;
FUNCTION_NAME IO_SIZE FILE_NAME IO_LATENCY
------------- ------- ------------------------------- -----------
LGWR 16 /u03/oradata/MYDB/control01.ctl 745
LGWR 16 /u03/oradata/MYDB/control01.ctl 506
LGWR 12 /u02/oradata/MYDB/redo09.dbf 705
LGWR 1 /u02/oradata/MYDB/redo08.dbf 502
LGWR 5 /u02/oradata/MYDB/redo07.dbf 538
LGWR 211 /u02/oradata/MYDB/redo10.dbf 1783
LGWR 1024 /u02/oradata/MYDB/redo10.dbf 597
LGWR 0 /u02/oradata/MYDB/redo10.dbf 597
LGWR 10 /u02/oradata/MYDB/redo10.dbf 597
LGWR 2 /u02/oradata/MYDB/redo10.dbf 775
LGWR 0 /u02/oradata/MYDB/redo07.dbf 683
LGWR 0 /u02/oradata/MYDB/redo09.dbf 704
LGWR 1 /u02/oradata/MYDB/redo10.dbf 504
LGWR 0 /u02/oradata/MYDB/redo10.dbf 690
LGWR 16 /u03/oradata/MYDB/control01.ctl 504
LGWR 58 /u02/oradata/MYDB/redo08.dbf 705
LGWR 1 /u02/oradata/MYDB/redo08.dbf 704
...
Obviously the trace files are also tagged with the timestamp of occurrence, whereas the view does not expose this infromation.
But let’s just say two things here – (a) where there is a will there is a way, and (b) like most V$ views, it is based on an X$ object, which might contain more information 
For other types of I/O in the database, you can also take a look at V$IO_OUTLIER
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