Oracle FAQ Your Portal to the Oracle Knowledge Grid
HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US
 

Home -> Community -> Mailing Lists -> Oracle-L -> Re: log file single write and log file parallel write

Re: log file single write and log file parallel write

From: Tom Pall <tom_at_cdproc.com>
Date: Wed, 6 Sep 2000 16:25:46 -0500
Message-Id: <10611.116352@fatcity.com>


This is a multi-part message in MIME format.

------=_NextPart_000_066B_01C0181F.1C371A80 Content-Type: text/plain;

        charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

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

------=_NextPart_000_066B_01C0181F.1C371A80 Content-Type: text/html;

        charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content=3Dtext/html;charset=3Diso-8859-1 =
http-equiv=3DContent-Type>
<META content=3D"MSHTML 5.00.2314.1000" name=3DGENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<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>&nbsp;</DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" size=3D2>log file=20
sync</FONT></STRONG></DIV>
<DIV>&nbsp;</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>&nbsp;</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>&nbsp;</DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" =
size=3D2></FONT></STRONG>&nbsp;</DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" size=3D2>log file single=20
write</FONT></STRONG></DIV>
<DIV>&nbsp;</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>&nbsp;</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>&nbsp;</DIV>
<DIV><STRONG><FONT face=3D"Comic Sans MS" size=3D2>log file parallel=20
write</FONT></STRONG></DIV>
<DIV>&nbsp;</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>&nbsp;</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>&nbsp;</DIV>
  <DIV><FONT color=3D#000000 size=3D2>What does the 'l<FONT =
face=3D"Courier New"=20
  size=3D2>og file single write' <FONT face=3DArial>event=20   mean?</FONT></FONT></FONT></DIV>
  <DIV><FONT color=3D#000000 size=3D2><FONT face=3D"Courier New" = size=3D2><FONT=20
  face=3DArial></FONT></FONT></FONT>&nbsp;</DIV>   <DIV><FONT color=3D#000000 size=3D2><FONT face=3D"Courier New" = size=3D2><FONT=20
  face=3DArial>What is the difference with 'l<FONT face=3D"Courier New" = size=3D2>og=20
  file parallel write' <FONT face=3DArial>event=20   ?</FONT></FONT></FONT></FONT></FONT></DIV>   <DIV><FONT color=3D#000000 size=3D2><FONT face=3D"Courier New" = size=3D2><FONT=20
  face=3DArial><FONT face=3D"Courier New" size=3D2><FONT=20   face=3DArial></FONT></FONT></FONT></FONT></FONT>&nbsp;</DIV>
  <DIV>&nbsp;</DIV>
  <DIV>&nbsp;</DIV>
  <DIV><FONT size=3D2>In one of my databases I have:</FONT></DIV>
  <DIV>&nbsp;</DIV>
  <DIV><FONT color=3D#000000=20

  =
size=3D2>Event&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp= ;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;= &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20   Average Wait</FONT></DIV>
  <DIV>&nbsp;</DIV>
  <DIV>log file=20
  =
sync&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb= sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20   3.69</DIV>
  <DIV>log file single =
write&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20   1.21 </DIV>
  <DIV>log file parallel write&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = 3.80=20
  </DIV>
  <DIV>&nbsp;</DIV>
  <DIV>&nbsp;</DIV>
  <DIV><FONT color=3D#000000 size=3D2>From this, can I say that my sync =
cost ratio=20
  is 3.69/(1.21+3.80)=3D0.73</FONT></DIV>   <DIV><FONT color=3D#000000 size=3D2></FONT><FONT size=3D2>That means = that 73% of=20
  LGWR writes takes place due to Sync Writes (Commit Statements) and=20   </FONT></DIV>
  <DIV><FONT size=3D2>that only 27% of them are due to background writes = (log=20
  buffer above _log_io_size).</FONT></DIV>
  <DIV><FONT color=3D#000000 size=3D2>Is this correct ???</FONT></DIV>
  <DIV><FONT color=3D#000000 size=3D2></FONT>&nbsp;</DIV>
  <DIV><FONT size=3D2>Thanks</FONT></DIV>
  <DIV>&nbsp;</DIV>
  <DIV>&nbsp;</DIV>
Received on Wed Sep 06 2000 - 16:25:46 CDT

Original text of this message

HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US