IDS Forum

Re: LOGBUFF Setting

Posted By: Fernando Nunes
Date: Wednesday, 25 January 2017, at 8:12 p.m.

In Response To: Re: LOGBUFF Setting (John Miller iii)

On a busy OLTP system with UNBUFFERED LOGGING, increasing the LOGBUFF size
will hardly improve performance.
My point is simple... if you run "onstat -l" you'll see something like:

Logical Logging
Buffer bufused bufsize numrecs numpages numwrits recs/pages
pages/io
L-1 0 64 1083329 101140 34419 10.7
2.9

Subsystem numrecs Log Space used

OLDRSAM 1082915 154473756

SBLOB 11 988

HA 403 17732

But almost for sure in the "pages/io" you'll see 1.x
That's because a busy OLTP system will be constantly COMMITing and
consequently constantly flushing the log buffer.
So, increasing the LOGBUFF will have two effects:

1- Get rid of that message... although it's highly improbable that the
worst case scenario would ever happen, you'll sleep better and that's good
2- You'll be "wasting" the increased size in memory (* 3) which nowadays is
completely irrelevant. If you're using HDR, it will be "* 15" (3 for the
normal buffers and 12 more for the replication buffers - and here I have
some doubts if it will have any effect. Eventually yes, it may reduce your
G flags on the primary, in case you have them....)

So, in conclusion, for the quality of your sleep, just get on with it :)

Regards.

On Wed, Jan 25, 2017 at 3:59 PM, John Miller iii <miller3@us.ibm.com> wrote:

> I think you might be mixing up LOGBUF and LOGSIZE. The logical log buffer
> is a buffer
> that can group logical log records together before writing them to disk.
> If you have
> unbuffered logging then every commit from an unbuffered logging database
> will
> write this buffer to disk and not allow the commit to continue until the
> write
> has completed. So the data is always on disk for every commit.
>
> The warning you are receiving has to do with the size of a single log
> record. You can
> examine your logs with onlog and look at the size column. Logical Log
> records must
> fit into a single buffer and in your case you have a record which is larger
> than 128K.
>
> If you are not hurting for 1MB of memory I would suggest 512KB. There are
> three buffers
> so this means you will be using 1.5 MB of memory for the log buffers.
> There will be 0
> chance of additional loss of data by expanding these buffers, only a chance
> of wasting memory.
> If these buffers are undersized then there will be allot of extra I/O done.
> So increasing
> the size in your case my reduce the I/O to the disk the logical logs reside
> on.
>
> John F. Miller III
> miller3@us.ibm.com
>
> ids-bounces@iiug.org wrote on 01/25/2017 07:38:50 AM:
>
> > From: "Keith Simmons" <smiley73@gmail.com>
> > To: ids@iiug.org
> > Date: 01/25/2017 07:39 AM
> > Subject: Re: LOGBUFF Setting [38561]
> > Sent by: ids-bounces@iiug.org
> >
> > Dave
> >
> > Rule of thumb is that it should be large enough for the system
> throughput,
> > but not so large that you could not afford to lose that data in the case
> of
> > a catastrophic server event and you had to recover and roll-forward log
> > files. I too have a busy OLTP system and have LOGBUFF set to 256. You
> could
> > try 130 but I would suggest a bit bigger and would try 192 (binary-type
> > sizes always work better :-) ).
> >
> > Keith
> >
> > On 25 January 2017 at 14:40, Informix DBA <in4mixdba@gmail.com> wrote:
> >
> > > Hi,
> > >
> > > We are running Informix 11.70.FC7W2 on Solaris 11. We have been getting
>
> > > the following message in the online.log.
> > >
> > > 01/24/17 15:24:55 Checkpoint log record may not fit into the logical
> log
> > > buffer.
> > > Recommended minimum value for LOGBUFF is 130.
> > >
> > > We currently have LOGBUFF set to 128 and RTO=5FSERVER=5FRESTART 0. We
> a=
> re
> > > running a busy OLTP system with unbuffered DB's.
> > >
> > > What is the recommended setting for LOGBUFF and how to you calculate
> it?
> > >
> > > Thank You,
> > >
> > > --Dave
> > >
> > > --f403045ea5243e29980546ec366e
> > >
> > >
> > > ************************************************************
> > > *******************
> > > Forum Note: Use "Reply" to post a response in the discussion forum.
> > >
> > >
> >
> > --001a1145ac32c8f2eb0546ed0650
> >
> >
> >
> ************************************************************
> ***************=
> ****
>
> > Forum Note: Use "Reply" to post a response in the discussion forum.
> >
>
>
> ************************************************************
> *******************
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>

--
Fernando Nunes
Portugal

http://informix-technology.blogspot.com
My email works... but I don't check it frequently...

--001a113fd9a27cb6e10546f509ec

Messages In This Thread

• LOGBUFF Setting
  Informix DBA -- Wednesday, 25 January 2017, at 9:40 a.m.
  • Re: LOGBUFF Setting
    Andreas Legner -- Wednesday, 25 January 2017, at 10:34 a.m.
  • Re: LOGBUFF Setting
    Keith Simmons -- Wednesday, 25 January 2017, at 10:38 a.m.
    • Re: LOGBUFF Setting
      John Miller iii -- Wednesday, 25 January 2017, at 10:59 a.m.
      • Re: LOGBUFF Setting
        Informix DBA -- Wednesday, 25 January 2017, at 3:23 p.m.
      • Re: LOGBUFF Setting
        Fernando Nunes -- Wednesday, 25 January 2017, at 8:12 p.m.
  • Re: LOGBUFF Setting
    Madison Pruet -- Wednesday, 25 January 2017, at 11:09 a.m.

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