IDS Forum

Re: Log reader to get transactions - failed HD....

Posted By: Madison Pruet
Date: Wednesday, 17 May 2017, at 10:25 a.m.

In Response To: Re: Log reader to get transactions - failed HD.... (Art Kagel)

What a lot of people forget is that buffered snd unbuffered logging is not a database property but rather a transactional property. The database propetty is only the default transactional property and can be changed for any transaction by using the set log command . I've recommend if you are using buffered logging that you might want to have a background program always running that updates a single row, uses unbuffered logging, commits, and then sleeps for X seconds. That way you can ensure that any committed transaction can remain in the buffer longer than X seconds.

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On Tue, May 16, 2017 at 3:26 PM, Art Kagel<art.kagel@gmail.com> wrote: It is possible if the databases are all BUFFERED LOG and the logical log
buffers are fairly large that the COMMIT records from multiple transactions
never made it to disk and so were not forwareded to the secondary. If that
happened those transactions would have rolled back on the primary when it
was promoted. If you look in the message log from the time of the promotion
you will see a number of transactions rolled back listed there. If it isn't
zero then there is the possibility that one or more of those transactions
had been committed on the primary but the logical log buffer was never
flushed if your databases are BUFFERED LOG. That is the risk of buffered
logging versus UNBUFFERED LOG which flushes the logical log buffer
immediately when a COMMIT is written to it.

But for a COMMIT to sit in the log buffer for most of an hour? That's
unusual unless the transaction was committed during a very quiet time and
there were no checkpoints during that hour (checkpoints also force a log
buffer write out). Your CKPTINTVL should be far less than an hour (3600
sec) but with RTO or AUTO_CKPT set there is a possibility of no checkpoints
for long periods if the server is fairly quiet. Again a data loss risk and
the reason I encourage my clients to not use RTO or AUTO_CKPT.

Art

Art S. Kagel, President and Principal Consultant
ASK Database Management
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 Tue, May 16, 2017 at 2:45 PM, LARRY SORENSEN <LSORENSEN25@msn.com> wrote:

> Thank you both. I didn't think that there was a real easy way to review the
> logical logs.
>
> I can't imagine how an hour's worth of data could me missing either. I
> swore
> up and down that, that could not happen because the servers were actively
> replicating. We just have one user that also swears that data is missing
> that
> he/she entered. (unless it was right before the server died and the
> transaction never completed)
>
> Larry
>
> ________________________________
> From: ids-bounces@iiug.org <ids-bounces@iiug.org> on behalf of
> david@smooth1.co.uk <david@smooth1.co.uk>
> Sent: Tuesday, May 16, 2017 1:38 PM
> To: ids@iiug.org
> Subject: Re: Log reader to get transactions - failed HD.... [39212]
>
> Not directly but...
>
> - onstat -l to check the current state of the logical logs
>
> - The current logical log will be marked with a "C" in the flags
>
> - Check in the online.log for message about when each Logical Log
> completed.
>
> - onlog -n logical-log-id > onlog.number.txt to dump each logical log
>
> - The output would need parsing to convert from partnums to table/index
> names
>
> - Logical log record formats are described at
>
> https://www.ibm.com/support/knowledgecenter/en/SSGU8G_11.
> 50.0/com.ibm.adref.doc/ids_adr_0358.htm
> IBM Knowledge
> Center<https://www.ibm.com/support/knowledgecenter/en/
> SSGU8G_11.50.0/com.ibm.adref.doc/ids_adr_0358.htm>
> www.ibm.com
> Welcome to IBM Knowledge Center: IBM's new home for technical product
> documentation. You can find product documentation here from over 3000 IBM
> products. In IBM Knowledge Center you can browse this documentation or
> search
> it to find the answers you need.
>
> - Note the begin work (BEGIN) record contains date and time!!
>
> - You can add -l to onlog to get more detail
>
> - You can use -d device to analyse logical log backups
>
> - onlog syntax is at
>
> https://www.ibm.com/support/knowledgecenter/en/SSGU8G_11.
> 50.0/com.ibm.adref.doc/ids_adr_0402.htm
> The onlog Utility -
> IBM<https://www.ibm.com/support/knowledgecenter/en/
> SSGU8G_11.50.0/com.ibm.adref.doc/ids_adr_0402.htm>
> www.ibm.com
> The onlog utility displays the contents of a logical-log file, either on
> disk
> or on backup.
>
> Regards,
> David.
>
> > On 16 May 2017 at 20:17 LARRY SORENSEN <LSORENSEN25@msn.com> wrote:
> >
> >
> > Solaris 10
> >
> > IDS 11.50.FC5
> >
> > SPARC 64
> >
> > I have a primary server and a secondary server. The primary server
> eventually
> > crashed, and we failed over to the secondary server. I told everyone that
> the
> > data should be current on the secondary, but now I am being told that it
> > appears that information changed during the last hour before the death of
> the
> > primary seems to be missing.
> >
> > Is there an elegant way to review the logs from the primary, which is
> > currently back up but not being used to find all the transactions/data
> changes
> > that took place during its final hour?
> >
> > Thank you.
> >
> > Larry
> >
> >
> >
>
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Messages In This Thread

• Log reader to get transactions - failed HDR Primar
  LARRY SORENSEN -- Tuesday, 16 May 2017, at 3:17 p.m.
  • Re: Log reader to get transactions - failed HDR Pr
    Art Kagel -- Tuesday, 16 May 2017, at 3:31 p.m.
  • Re: Log reader to get transactions - failed HDR Pr
    david@smooth1.co.uk -- Tuesday, 16 May 2017, at 3:38 p.m.
    • Re: Log reader to get transactions - failed HD....
      LARRY SORENSEN -- Tuesday, 16 May 2017, at 3:45 p.m.
      • Re: Log reader to get transactions - failed HD....
        Art Kagel -- Tuesday, 16 May 2017, at 4:25 p.m.
        • Re: Log reader to get transactions - failed HD....
          Madison Pruet -- Wednesday, 17 May 2017, at 10:25 a.m.
        • Re: Log reader to get transactions - failed HD....
          Art Kagel -- Wednesday, 17 May 2017, at 10:28 a.m.

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