[Linux-ha-dev] pgsql RA improvements

[Serge Dubrouski]

And I don't like the idea of removing PID in "start" function. The
standard approach if to remove it after stopping application. Other
way it could lead to attempt of starting a second copy of application.

On 2/23/07, Serge Dubrouski <sergeyfd at gmail.com> wrote:
> I like the idea of the patch, but honestly I don't like how it's
> implemented. It shall call (as Andrew suggested) "monitor" function to
> check that pgsql is up or down instead of spreading the same code all
> around the script. I'd like to review the idea and prepare another
> patch if everybody is agree.
>
> On 2/23/07, Keisuke MORI <kskmori at intellilink.co.jp> wrote:
> > Hi,
> >
> > We have found a several problems with pgsql RA through our testing.
> > It 'fails to failover' in some scenarios.
> > I'm proposing a patch to fix them.
> >
> > Problem description:
> >
> > 1) The first 'monitor' may fail even if the postmaster was
> >   successfully launched.
> >
> >   This is because 'start' of the pgsql may return before the
> >   postmaster gets ready to answer to a psql query issued by
> >   'monitor', since it only checks the existance of postmaster
> >   process. The postmaster can take a few minitues to get ready
> >   to answer, particularly when it needs to recover the database
> >   after a crash. Even if no recovery is necessary, we observed
> >   that it sometimes fails in some of our test cases.
> >
> > 2) The postmaster fails to startup when 'postmaster.pid' file
> >   was left over from the previous crash.
> >
> > 3) 'stop' doest not execute the fast mode shutdown effectively,
> >   because it executes the immediate mode shutdown at the very
> >   next moment.  The fast mode shutdown can take a few minutes
> >   to complete to flush the database log.
> >
> >   This isn't a critical problem, but it may result to take a
> >   time longer to complete the failover (according to our
> >   database team). It is preferable to wait to complete the fast
> >   mode shutdown as long as possible.
> >
> >
> > Proposals to fix:
> >
> > 1) In 'start', wait until the postmaster gets ready to answer by
> >   checking as same as 'monitor' does.
> >   The maximum wait time to complete to startup can be
> >   customized by an additional parameter 'start_wait'.
> >
> > 2) Add a cleanup code for 'postmaster.pid' when stop and before starting.
> >
> > 3) In 'stop', wait until the postmaster completes to the fast
> >   mode shutdown.
> >   The maximum wait time to complete to shutdown can be
> >   customized by an additional parameter 'stop_wait.
> >
> >
> > The attached patch is for the latest -dev.
> >
> > Regards,
> >
> > Keisuke MORI
> > NTT DATA Intellilink Corporation
> >
> >
> > _______________________________________________________
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> >
> >
> >
>