You'll sometimes see user threads in log-buffer-wait (onstat -u flags
column has a B) and onstat -l shows, uhmmm, i don't recall exactly what
it says - something about waiting in the header, but it boils down to
not being able to switch to the next log buffer (of the three (triple
buffering)) when the log buffer hasn't been replicated to the secondary
(or at least we've no reply yet from the secondary - check with onstat
-g ath you'll see the hdr threads run).

When the primary goes into a checkpoint it may wait (possibly very long)
for a session to leave critical section which it can't because it's
waiting on a log buffer.

Getting any useful stats out of the secondary sucks in general. Other
than that i quite like HDR.

> -----Original Message-----
> From: owner-informix-list@iiug.org
> [mailtowner-informix-list@iiug.org] On Behalf Of TBP
> Sent: 19 May 2004 10:42
> To: informix-list@iiug.org
> Subject: Re: Extremly long checkpoints: How to find the
> reason and solve the
>
>
> Francisco Roldan wrote:
> > Are you Replicating to other server ?
> > Some time ago I got very long checkpoints in an
> > Informix Server with High Availability Data Replication (HDR)
> > on the primary server.
> >
> > I found out that the reason was an extremely complex query
> > executed in the secondary server (Stand By Server) for generating
> > a report (DSS Reports in OLTP System , not a good idea !! ).
> >
> > Chekpoints for HDR Systems are always Synchronous .
> > It doesn't matter if you configure the system to be
> Asynchronous (I don't
> > remember
> > the name of the parameter in the Onconfig File), the only
> thing that really
> > gets Asynchronous are the transactions (No 2-Fase Commit Protocol),
> > the onconfig's parameter should be named TwoFaseCommit instead of
> > the name that I don't remember.
> > Primary Server Always wait an acknowledge message of the
> other servers
> > for finishing its own checkpoint.
> >
> > If you are not replicating ignore this message, I just
> wanted to express
> > my frustrating experience with HDR.
> > Enterprise Replication (ER) would solve the problem.
> >
> > Regards
> >
> >
> snip ...
>
> DRINTERVAL -1 (Synchronous) or DRINTERVAL > 0 Asynchronous
>
> There appears to be some activity which the checkpoint is
> dependent on
> (not the checkpoint itself) which is synchronous; you can see
> this when
> the checkpoint completes on the primary but hasn't started /
> completed
> on the secondary when DRINTERVAL > 0. Something to do with
> flushing the
> physical log buffer on the secondary, and threads in critical section.
>
> What was the "extremely complex query executed in the
> secondary server
> (Stand By Server) for generating a report (DSS Reports in
> OLTP System ,
> not a good idea !! )." (I thought that was a nice way to
> split out DSS
> from the OLTP primary by putting DSS on the secondary).
>
> Did you log a Tech Support case??
>
> Were there a lot of writes involved on the secondary to temp tables?
>

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