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Home -> Community -> Mailing Lists -> Oracle-L -> Re: log file single write and log file parallel write
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Look in your Oracle [Version #] Reference, in the Oracle Wait Events = section:
log file sync
When a user session commits, the session's redo information needs to be =
flushed to the redo logfile. The user session will post the LGWR to =
write the log buffer to the
redo log file. When the LGWR has finished writing, it will post the user =
session.=20
Wait Time: The wait time includes the writing of the log buffer and the = post.=20
log file single write
Waiting for the write to this logfile to complete. This event is used =
while updating the header of the logfile. It is signaled when adding a =
log file member and when
incrementing sequence numbers.=20
Wait Time: Time it takes for the physical I/O (write) to complete.=20
log file parallel write
Writing redo records to the redo log files from the log buffer.=20
Wait Time: Time it takes for the I/Os to complete. Even though redo = records are written in parallel, the parallel write is not complete = until the last I/O is on disk.=20
Hi, hope somebody can help me
What does the 'log file single write' event mean?
=20
What is the difference with 'log file parallel write' event ?
=20
In one of my databases I have:
Event Average Wait log file sync 3.69 log file single write 1.21=20 log file parallel write 3.80=20
From this, can I say that my sync cost ratio is =
3.69/(1.21+3.80)=3D0.73
That means that 73% of LGWR writes takes place due to Sync Writes =
(Commit Statements) and=20
that only 27% of them are due to background writes (log buffer above =
_log_io_size).
Is this correct ???
=20
Thanks
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<DIV><FONT face=3D"Comic Sans MS" size=3D2><STRONG>Look in your Oracle =
[Version #]=20
Reference, in the Oracle Wait Events section:</STRONG></FONT></DIV>
<DIV> </DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" size=3D2>log file=20
sync</FONT></STRONG></DIV>
<DIV> </DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" size=3D2>When a user session =
commits, the=20
session's redo information needs to be flushed to the redo logfile. The =
user=20
session will post the LGWR to write the log buffer to the<BR>redo log =
file. When=20
the LGWR has finished writing, it will post the user session.=20
</FONT></STRONG></DIV>
<DIV> </DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" size=3D2>Wait Time: The wait =
time includes=20
the writing of the log buffer and the post. =
<BR></FONT></STRONG><STRONG><FONT=20
face=3D"Comic Sans MS" size=3D2></DIV></FONT></STRONG>
<DIV><STRONG><FONT face=3D"Comic Sans MS" =
size=3D2></FONT></STRONG> </DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" =
size=3D2></FONT></STRONG> </DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" size=3D2>log file single=20
write</FONT></STRONG></DIV>
<DIV> </DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" size=3D2>Waiting for the write =
to this=20
logfile to complete. This event is used while updating the header of the =
logfile. It is signaled when adding a log file member and =
when<BR>incrementing=20
sequence numbers. </FONT></STRONG></DIV>
<DIV> </DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" size=3D2>Wait Time: Time it =
takes for the=20
physical I/O (write) to complete. </FONT></STRONG></DIV>
<DIV> </DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" size=3D2>log file parallel=20
write</FONT></STRONG></DIV>
<DIV> </DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" size=3D2>Writing redo records =
to the redo=20
log files from the log buffer. </FONT></STRONG></DIV>
<DIV> </DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" size=3D2>Wait Time: Time it =
takes for the=20
I/Os to complete. Even though redo records are written in parallel, the =
parallel=20
write is not complete until the last I/O is on disk. =
<BR></FONT></STRONG></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: =
0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A href=3D"mailto:dcutrone_at_afip.gov.ar" =
title=3Ddcutrone_at_afip.gov.ar>Diego=20
Cutrone</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
href=3D"mailto:ORACLE-L_at_fatcity.com"=20
title=3DORACLE-L_at_fatcity.com>Multiple recipients of list ORACLE-L</A> =
</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Wednesday, September 06, =
2000 2:10=20
PM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> log file single write =
and log=20
file parallel write</DIV>
<DIV><BR></DIV> <DIV><FONT color=3D#000000 size=3D2>Hi, hope somebody can help = me</FONT></DIV> <DIV> </DIV> <DIV><FONT color=3D#000000 size=3D2>What does the 'l<FONT =face=3D"Courier New"=20
<DIV> </DIV> <DIV> </DIV> <DIV><FONT size=3D2>In one of my databases I have:</FONT></DIV> <DIV> </DIV> <DIV><FONT color=3D#000000=20
</DIV> <DIV> </DIV> <DIV> </DIV> <DIV><FONT color=3D#000000 size=3D2>From this, can I say that my sync =cost ratio=20
<DIV><FONT color=3D#000000 size=3D2>Is this correct ???</FONT></DIV> <DIV><FONT color=3D#000000 size=3D2></FONT> </DIV> <DIV><FONT size=3D2>Thanks</FONT></DIV> <DIV> </DIV> <DIV> </DIV>Received on Wed Sep 06 2000 - 16:25:46 CDT
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