RV: 'log file single write' and 'log file parallel write' - Solved

Tom, Steve:

        Don't pay attention to my last mail, I found the answer to my question in
http://www.ixora.com.au/q+a/0008/29172823.htm.

Thanks again

-----Mensaje original-----
De: Diego Cutrone <dcutrone_at_afip.gov.ar> Para: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Fecha: Jueves 7 de Septiembre de 2000 2:54 PM Asunto: RE: 'log file single write' and 'log file parallel write'

>Tom, Steve, thanks for answering (please forgive my poor english)
>
>(AIX, Oracle 7.3.4)
>
>Steve, as a matter of fact, this question came to me whan I was running
your
>script "lgwr_stats".
>Some time ago it was reporting a sync cost ratio of 1.20 !!!
>To combat this I set _log_io_size=24 (my log block size is 512 bytes) and
>the sync cost ratio is
>about 0.90 now.
>
>But what I don't understand is how could the ratio be greater than "1", I
>think this is not possible.
>To get this ratio you divide (average log file sync wait/average log file
>parallel write), where
>log file sync wait= it is the time it takes the LGWR to flush the
log_buffer
>data to disk only when a
> commit takes place.
>log file parallel write wait= it is the time it takes the LGWR to flush the
>log_buffer data to disk whenever
> a commit takes place (sync write) or when a
>background syncs takes place.
>
>According to this, "log file parallel write wait" includes "log file sync
>wait", so how can it be possible that
>this ratio was greater than 1.
>
>I'm sure I'm missing something here, could you please tell me what?
>
>
>
>
>
>
>
>
>
>-----Mensaje original-----
>De: Steve Adams <steve.adams_at_ixora.com.au>
>Para: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
>Fecha: Jueves 7 de Septiembre de 2000 1:42 AM
>Asunto: 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/
>>@
>>@ Going to OpenWorld?
>>@ Catch the Ixora performance tuning seminar too!
>>@ See http://www.ixora.com.au/seminars/ for details.
>>
>>
>>-----Original Message-----
>>Sent: Thursday, 7 September 2000 5:11
>>To: Multiple recipients of list ORACLE-L
>>
>>
>>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
>>log file parallel write 3.80
>>
>>
>>From this, can I say that my sync cost ratio is 3.69/(1.21+3.80)=0.73
>>That means that 73% of LGWR writes takes place due to Sync Writes
>>(Commit Statements) and
>>that only 27% of them are due to background writes (log buffer above
>>_log_io_size).
>>Is this correct ???
>>
>>Thanks
>>
>>--
>>Author: Steve Adams
>> INET: steve.adams_at_ixora.com.au
>>
>>Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
>>San Diego, California -- Public Internet access / Mailing Lists
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>
>--
>Author: Diego Cutrone
> INET: dcutrone_at_afip.gov.ar
>
>Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
>San Diego, California -- Public Internet access / Mailing Lists
>--------------------------------------------------------------------
>To REMOVE yourself from this mailing list, send an E-Mail message
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Received on Thu Sep 07 2000 - 14:08:46 CDT