RE: 'log file single write' and 'log file parallel write'

Hello Diego,

The 'log file single write' event is associated with writes to the log file header blocks only, and that only happens when a log file is being opened or closed. Header block writes have to be single writes (rather than parallel writes to all the members of the group) because part of the header information is the file number, and that is different for each member. These waits are rare and occur in the background anyway, so I suggest that you not concern yourself with them.

The 'log file parallel write' event is used for routines writes of sets of redo blocks by LGWR. It is interesting only as a point of comparison for the 'log file sync' time, which is what the Ixora "sync cost ratio" does. Both your calculation of the sync cost ratio, and your interpretation of it are incorrect. Please use the lgwr_stats.sql script at http://www.ixora.com.au/scripts/redo_log.htm#lgwr_stats to calculate the ratio, and check the recent answer at http://www.ixora.com.au/q+a/0008/29172823.htm for some guidelines on how to interpret the number. If you want to know the ratio of background writes to sync writes, then use the 'redo writes' and 'redo synch writes' statistics from V$SYSSTAT instead.

@ Regards,
@ Steve Adams
@ http://www.ixora.com.au/
@ http://www.christianity.net.au/

@

-----Original Message-----
From: Diego Cutrone [mailto:dcutrone_at_afip.gov.ar] Sent: Thursday, 7 September 2000 5:11
To: Multiple recipients of list ORACLE-L Subject: log file single write and log file parallel write

Hi, hope somebody can help me

What does the 'log file single write' event mean?

What is the difference with 'log file parallel write' event ?

In one of my databases I have:

Event                                 Average Wait

log file sync                     3.69
log file single write         1.21