IDS Forum

Re: LOGBUFF size

Posted By: Madison Pruet
Date: Saturday, 28 May 2016, at 8:15 a.m.

In Response To: Re: LOGBUFF size (Art Kagel)

blockquote, div.yahoo_quoted { margin-left: 0 !important; border-left:1px #715FFA solid !important; padding-left:1ex !important; background-color:white !important; } Also you might want to consider having a transaction running periodically that is using unbuffered logging update a single row. That would be enough to force a flush of the current log buffer and therefor set an upper limit on the in flight data.

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On Saturday, May 28, 2016, 3:12 AM, Art Kagel <art.kagel@gmail.com> wrote:

If you try buffered logging, remember that your average log buffer flush is
only writing 1.2pages so your transactions are fairly small so set the
logical log buffers smaller rather than larger to reduce the data in flight
and therefore at risk if you crash.

Art

Art S. Kagel, President and Principal Consultant
ASK Database Management
ASK Database Management

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ASK Database Management

Database Consulting and Support
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Blog: http://informix-myview.blogspot.com/

Disclaimer: Please keep in mind that my own opinions are my own opinions
and do not reflect on the IIUG, nor any other organization with which I am
associated either explicitly, implicitly, or by inference. Neither do
those opinions reflect those of other individuals affiliated with any
entity with which I am affiliated nor those of the entities themselves.

On Sat, May 28, 2016 at 12:51 AM, FRANK <yunyaoqu@gmail.com> wrote:

> Thanks Art and Andrew for the info!
>
> We have a lot of small transactions , about one million per hour.
>
> So, when each COMMIT trigger a buffer flush, it would have a high
> frequent IO flush.... ( reducing this might help bigger ??)
>
> Our system is quite reliable( no frequent crash) , as Andrew
> benchmarked, buffered logging might help ... to be explored ...
>
> Thanks
> Frank
>
> On Thu, May 26, 2016 at 4:19 PM, Art Kagel <art.kagel@gmail.com> wrote:
>
> > First, if your databases are UNBUFFERED or ANSI mode logged then the size
> > of the logical log buffer is not important and increasing it will not
> > improve performance at all since the buffer is flushed whenever a COMMIT
> > record is written to it not when it is filled.
> >
> > That said, even if all of your databases are BUFFERED log, the write
> > performance of the chunks containing the logical log is the biggest
> factor
> > in determining whether the logical log buffers flush quickly enough to
> > prevent sessions from having to wait for them to flush. In a BUFFERED log
> > situation, bigger logical log buffers will sometimes help here, but keep
> in
> > mind that the bigger the buffer is the more data is at risk for
> > catastrophic loss if the server crashes with many transactions still
> > unflushed. You have to balance safety with performance.
> >
> > Recommendation: Move the logical logs to a faster or less active disk
> > structure.
> >
> > Art
> >
> > Art S. Kagel, President and Principal Consultant
> > ASK Database Management
> > http://www.askdbmgt.com
> >
> > Blog: http://informix-myview.blogspot.com/
> >
> > Disclaimer: Please keep in mind that my own opinions are my own opinions
> > and do not reflect on the IIUG, nor any other organization with which I
> am
> > associated either explicitly, implicitly, or by inference. Neither do
> > those opinions reflect those of other individuals affiliated with any
> > entity with which I am affiliated nor those of the entities themselves.
> >
> > On Thu, May 26, 2016 at 12:28 PM, FRANK <yunyaoqu@gmail.com> wrote:
> >
> > > Hi,
> > >
> > > We set ,
> > >
> > > LOGBUFF 256
> > >
> > > Occasionally, I still see this sometimes,
> > >
> > > 58087a28 Y--P--- 4082303 saapmgr - 551cf760 0
> > > 1 0 0
> > > 580882e8 G-BPX-- 3671545 saapmgr - 526d0898 0
> > > 2 29 48411
> > > 58088ba8 Y--P--- 2478091 saapmgr - 55a96230 0
> > > 1 116 14986
> > >
> > > So, a session is waiting for the log buffer .
> > >
> > > The doc ( below) seems not to recommend to set it higher or .... .
> > >
> > > What do you think or comments ?
> > >
> > > Thanks
> > > Frank
> > >
> > > LOGBUFF configuration parameter
> > >
> > > Use the LOGBUFF configuration parameter to specify the size in
> kilobytes
> > > for the three logical-log buffers in shared memory.
> > > onconfig.std value LOGBUFF 64 units Kilobytes values An integer in the
> > > range of 32 - (32767 * pagesize / 1024), where pagesize is the default
> > > system page size. The value must be evenly divisible by the default
> > system
> > > page size. If the value is not evenly divisible by the page size, the
> > > database server rounds down the size to the nearest value that is
> evenly
> > > divisible by the page size. takes effect After you edit your onconfig
> > file
> > > and restart the database server.
> > > Usage
> > >
> > > The three logical log buffers permit user threads to write to the
> active
> > > buffer while one of the other buffers is being flushed to disk. If
> > flushing
> > > is not complete by the time the active buffer fills, the user thread
> > begins
> > > writing to the third buffer.
> > >
> > > If the RTO_SERVER_RESTART configuration parameter is enabled, set the
> > value
> > > of the LOGBUFF configuration parameter to 256 kilobytes. If the value
> of
> > > the LOGBUFF configuration parameter is less than 256 kilobytes, a
> warning
> > > message displays when you restart the server.
> > >
> > > Otherwise, set the value of the LOGBUFF configuration parameter to 32
> > > kilobytes for standard workloads or 64 kilobytes for heavy workloads.
> The
> > > database server uses the LOGBUFF parameter to set the size of internal
> > > buffers that are used during recovery. If you set LOGBUFF too high, the
> > > database server can run out of memory and shut down during recovery.
> > >
> > > If you log user data in smart large objects, increase the size of the
> log
> > > buffer to make the system more efficient. The database server logs only
> > the
> > > portion of a smart-large-object page that changed.
> > >
> > > You can view information about the logical log buffers by running the
> > > onstat
> > > -l command.
> > > *Parent topic:* Database configuration parameters
> > >
> > > <
> > >
> >
> >
>
>
http://www.ibm.com/support/knowledgecenter/SSGU8G_12.1.0/com.ibm.adref.doc/ids_adr_0007.htm?lang=en-us
> > > >
> > > *Related reference*:
> > > onstat -l command: Print physical and logical log information
> > >
> > > <
> > >
> >
> >
>
>
http://www.ibm.com/support/knowledgecenter/SSGU8G_12.1.0/com.ibm.adref.doc/ids_adr_0598.htm?lang=en-us
> > > >
> > >
> > > --001a11c1728c309b400533c148a4
> > >
> > >
> > >
> > >
> >
> >
>
>
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Messages In This Thread

• LOGBUFF size
  FRANK -- Thursday, 26 May 2016, at 12:28 p.m.
  • Re: LOGBUFF size
    Fernando Nunes -- Thursday, 26 May 2016, at 1:27 p.m.
    • Re: LOGBUFF size
      FRANK -- Thursday, 26 May 2016, at 2:26 p.m.
      • Re: LOGBUFF size
        Fernando Nunes -- Thursday, 26 May 2016, at 3:18 p.m.
        • RE: LOGBUFF size
          Andrew Ford -- Thursday, 26 May 2016, at 3:30 p.m.
        • Re: LOGBUFF size
          FRANK -- Friday, 27 May 2016, at 10:34 a.m.
          • Re: LOGBUFF size
            Fernando Nunes -- Sunday, 29 May 2016, at 4:37 a.m.
          • Re: LOGBUFF size
            Fernando Nunes -- Wednesday, 3 August 2016, at 12:30 p.m.
  • Re: LOGBUFF size
    Art Kagel -- Thursday, 26 May 2016, at 4:19 p.m.
    • Re: LOGBUFF size
      FRANK -- Friday, 27 May 2016, at 10:51 a.m.
      • Re: LOGBUFF size
        Art Kagel -- Saturday, 28 May 2016, at 4:11 a.m.
        • Re: LOGBUFF size
          Madison Pruet -- Saturday, 28 May 2016, at 8:15 a.m.

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