Hi, Francisco,

During 'normal' idle secondary operation, the real discrepancy between
primary and secondary is very small - just few seconds
in the case of unbuffered logging.

Note, that secondary doesn't apply changes immediately:
it keeps log records in the 'log receive' buffer while
'drsecapply' thread lazily applies those changes.
If secondary server is busy, then the amount of records
to apply during the checkpoint on the secondary might be
big enough to cause much longer checkpoints.

In the case of buffered logging on the primary, the pattern is even
worse: the primary flushes it's replication buffer only when it fills
(data replication buffer has the same size as logical log buffer) or
when 'DRINTERVAL' expires. This is why one should expect, that
with buffered logging in the presence of HDR checkpoints
are longer.

Then,
1. What is LOGBUFF in Your case? May be, You can decrease it
2. You can decrease DRINTERVAL
3. You can try to switch to unbuffered log
on primary if You have dedicated disk (array) for logical log
4. Improve the disk layout on secondary

------------------------------------------
Alexey Sonkin
Senior Database Administrator


> -----Original Message-----
> From: Francisco Roldan [mailto:froldan@5b.com.gt]
> Sent: Monday, October 06, 2003 6:13 PM
> To: Alexey Sonkin; informix-list@iiug.org
> Subject: RE: Checkpoint Duration - HDR - Sync/Async
>
> Thanks Alexey,
> i really appreciate your help
>
> I think that the dss query was taking
> disk resources, but regardless of
> cpu or disk resources, I think that
> when a ckeckpoint occurs, Informix stops
> running any query (even already started querys)
> and doesn't execute new ones, and
> then execute the checkpoint, am i right?
>
> Could you explain me a little more about
> what you mention about rolling forward logical
> log records received from the primary ?
>
> I am sure that i am not the first person
> who implements HDR for high availability purposes,
> and for executing DSS querys on the secondary server,
> so i think that i am missing something.
>
> Thanks
>
> Regards
>
>
> -----Mensaje original-----
> De: Alexey Sonkin [mailto:alexeis@grandvirtual.com]
> Enviado el: Lunes, 06 de Octubre de 2003 02:47 p.m.
> Para: 'Francisco Roldan'; informix-list@iiug.org
> Asunto: RE: Checkpoint Duration - HDR - Sync/Async
>
>
>
>
> Hi, Francisco,
>
> The problem is that DSS query on secondary might take a lot of CPU/disk
> resources that a requred to roll forward logical log records received from
> the primary.
>
> The first thing to do is to define whether it's CPU
> or disk bottneck on the secondary
>
> ------------------------------------------
> Alexey Sonkin
> Senior Database Administrator
>
>
> > -----Original Message-----
> > From: Francisco Roldan [mailto:froldan@5b.com.gt]
> > Sent: Friday, October 03, 2003 11:48 AM
> > To: informix-list@iiug.org
> > Subject: RV: Checkpoint Duration - HDR - Sync/Async
> >
> > Hi everyboy,
> >
> > I really would appreciate your comments about this subject.
> >
> > Thanks in advance
> >
> > -----Mensaje original-----
> > De: Francisco Roldan [mailto:froldan@5b.com.gt]
> > Enviado el: Miércoles, 01 de Octubre de 2003 12:30 p.m.
> > Para: informix-list@iiug.org
> > Asunto: Checkpoint Duration - HDR - Sync/Async
> >
> > Hi everybody,
> > my environment :
> >
> > Two identical servers running AIX 4.3.3 - IDS 7.3.1 UD1 running HDR
> > between both database servers
> > DRINTERVAL : 360 segs (=> ASYNCHRONOUS)
> > I have only one production database on Buffered Logging Mode.
> >
> > I implemented HDR in order to protect the data changed after the last
> > backup, and to be able to execute reports/DSS-querys on the secondary
> > server (in that order).
> >
> > I read that the checkpoint between primary and secondary servers
> > running HDR are synchronous, regardless of DRINTERVAL parameter is
> > -1 (=> SYNCHRONOUS) or not.
> >
> > When i execute a very heavy dss query on my secondary server, it
> > affects the performance on this server and i have noticed that it
> > affects the duration of the checkpoint on both servers (even getting 6
> > times the normal duration).
> > It is logic if i consider that the checkpoints between primary and
> > secondary
> > servers are synchronous, am i right ? or am i missing something else
> that
> > could be affecting the checkpoints duration on both servers?
> >
> > Is it possible to minimize the impact on the primary server's
> > checkpoint duration ? For examble by tunning some parameters like
> > DRINTERVAL, CKPTINTVL(240 segs. on my servers), or the difference
> > between these values (I am just guessing). Or the Logging mode on my
> > only production database.
> >
> > Thanks in advance
> >
> > Regards
> >
> >
> > sending to informix-list
> >
> > sending to informix-list

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