Thanks for the response Steve...It was really helpful:
Below are some doubts I wanted to clarify..please read and suggest.
Can we also check if replication was broken earlier...somehow due to power
failure of some other reasons in past...The reason I am asking is I am
getting some discrepancies in data between master and slave...? I want to
know the reason of it...
thanx
On Thu, Nov 29, 2012 at 12:32 AM, Steve Crawford <
scrawf...@pinpointresearch.com> wrote:
> On 11/28/2012 10:21 AM, Shams Khan wrote:
>
>> ...how do we ensure my replication is working fine?...
>>
>>
> Below is the core of one of my bash-script tools. It could use some
> tweaking (comments welcome) but works well. The script is run every minute
> by cron on master and standby servers. It auto-determines whether the
> server is currently a master or standby so the same script can be deployed
> to all servers.
>
> If a master-server, it updates a one-record test table with a current
> timestamp to ensure there is activity on the master.
>
> If a standby-server, it determines the lag based both on the age of
> pg_last_xact_replay_timestamp(**) and on the age of the record in the
> test table then returns the worst of the two.
>
> The delay value is set in $standby_delay which is a value in seconds. It's
> up to you to decide what constitutes an issue that requires attention (but
> remember that 60-seconds does not necessarily indicate a problem on an idle
> server). My first-level alert triggers at 130-seconds and I have never hit
> that much of a delay.
>
> #!/bin/bash
> #
> # Check PostgreSQL sync-status
> #
> # Requires table "sync_status" with column "sync_time" of type timestamp
> with time zone
>
>
> # We need a temp file
> tempquery="$(mktemp /tmp/monitor_db_**synchronizationXXXXXXXXXX)"
>
> # If master, update sync_status timestamp and return 0. If standby, check
> both age
> # of log-replay location and of timestamp in sync_status table and set
> $standby_delay
> # to the greater of the two (in seconds)
> #
> standby_delay=$(
> psql -q --tuples-only --no-align 2>/dev/null <<EOS
> \o ${tempquery}
> select
> case when setting='on' then
> '
> with logdelay as
> (
> select
> case when
> pg_last_xlog_receive_location(**)=pg_last_xlog_replay_**location() then
> 0::int
> else
> (extract(epoch from now())-extract(epoch from
> pg_last_xact_replay_timestamp(**)))::int
> end as replicadelay
> union
> select
> (extract(epoch from now())-extract(epoch from sync_time))::int as
> replicadelay
> from
> sync_status
> )
> select
> max(replicadelay)
> from
> logdelay
> ;
> '
> else
> '
> begin;
> delete from sync_status;
> insert into sync_status (sync_time) values (now()) returning 0::int as
> replicadelay;
> commit;
> '
> end
> from pg_settings where name='transaction_read_only';
> \o
> \i ${tempquery}
> EOS
> )
>
> # Cleanup temp file
> test -f "${tempquery}" && rm "${tempquery}"
>
> # Do some alert based on the number of seconds of lag between master and
> standby here
>
> Cheers,
> Steve
>
>
>
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