Thread: Re: Notification or action when WAL archives fully restored andstreaming replication started

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Hi,
I've got master/slave replication setup between a few hosts. At any
point a slave could become a master. I've got appropriate locking in
place using an external system so that only one master can exist at a
time. I'm having trouble determining when my slaves are in sync with the
current master so that they can be a candidate for promotion. I want
some form of indicator _without reading a log_ when streaming
replication has started.

My recovery.conf for slaves:
  standby_mode = on
  restore_command = 'gunzip < /archives/wal/%f > %p'
  recovery_target_timeline = 'latest'
  primary_conninfo = 'host=PGSQL_FRONTEND_NAME port=5432
user=PGSQL_RECOVERY_USER password=PGSQL_RECOVERY_PASS'

Appropriate postgresql.conf:
  wal_level = replica
  archive_mode = on
  archive_command = 'test ! -f /archives/wal/%f && gzip < %p >
/archives/wal/%f'
  archive_timeout = 15min

Regards,
Michael Cassaniti
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On Thu, Mar 14, 2019 at 02:59:38PM +1100, Michael Cassaniti wrote:
> I've got master/slave replication setup between a few hosts. At any
> point a slave could become a master. I've got appropriate locking in
> place using an external system so that only one master can exist at a
> time. I'm having trouble determining when my slaves are in sync with the
> current master so that they can be a candidate for promotion. I want
> some form of indicator _without reading a log_ when streaming
> replication has started.

pg_stat_replication on the primary, no?  Here is its documentation:
https://www.postgresql.org/docs/11/monitoring-stats.html#MONITORING-STATS-VIEWS
--
Michael

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On 14/3/19 3:10 pm, Michael Paquier wrote:
> On Thu, Mar 14, 2019 at 02:59:38PM +1100, Michael Cassaniti wrote: >> I've got master/slave replication setup between
afew hosts. At any 
>> point a slave could become a master. I've got appropriate locking in
>> place using an external system so that only one master can exist at a
>> time. I'm having trouble determining when my slaves are in sync with
the >> current master so that they can be a candidate for promotion. I
want >> some form of indicator _without reading a log_ when streaming >>
replication has started. > > pg_stat_replication on the primary, no?
Here is its documentation: >
https://www.postgresql.org/docs/11/monitoring-stats.html#MONITORING-STATS-VIEWS
> -- > Michael This at least points me in the right direction. I need
something on the receiver side, so the state column in
pg_stat_wal_receiver might cover. I can check for state = streaming, but
the DB won't accept connections in standby mode.

Thanks for the quick reply.
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On 14/3/19 5:15 pm, Michael Cassaniti wrote:
> > On 14/3/19 3:10 pm, Michael Paquier wrote: > > On Thu, Mar 14, 2019
at 02:59:38PM +1100, Michael Cassaniti wrote: >> I've got master/slave
replication setup between a few hosts. At any > >> point a slave could
become a master. I've got appropriate locking in > >> place using an
external system so that only one master can exist at a > >> time. I'm
having trouble determining when my slaves are in sync with > the >>
current master so that they can be a candidate for promotion. I > want
>> some form of indicator _without reading a log_ when streaming >> >
replication has started. > > pg_stat_replication on the primary, no? >
Here is its documentation: > >
https://www.postgresql.org/docs/11/monitoring-stats.html#MONITORING-STATS-VIEWS
> > -- > Michael This at least points me in the right direction. I need
> something on the receiver side, so the state column in >
pg_stat_wal_receiver might cover. I can check for state = streaming, but
> the DB won't accept connections in standby mode. > > Thanks for the
quick reply. Actually I was wrong. For some reason my testing initially
didn't want to allow read-only connections. Problem solved.
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