[Linux-ha-dev] pgsql RA improvements

[Keisuke MORI]

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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