Thread: strem replication standby lag check

hi, all,

I know we can connect to primary and SELECT pg_current_xlog_location(); (eg.
'0/36A77900') to get primary xlog position then connect to the standby to do
the following to get the byte lag:

select pg_xlog_location_diff('0/36A77900',pg_last_xlog_replay_location());

0/36A77900 is the xlog position from primary.

My question is that is there a way I can connect to the primary on the
standby host using replica user which i already have the primary_conninfo in
the recovery.conf and get the result of SELECT pg_current_xlog_location();
of the primary so I can simply write a function on the standby to return the
lag in bytes in one call.

any way I can do that without a dblink?

Thank you if any one can help.

best,
Ying





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> 2014/1/17 yhe <yinghe0101@yahoo.com>
>> any way I can do that without a dblink?
>>

On Mon, Jan 20, 2014 at 4:33 AM, desmodemone <desmodemone@gmail.com> wrote:
> I think it's better to use the pg_stat_replication

+1

And this is how to make all the calculation of the lag (in bytes):

CREATE OR REPLACE FUNCTION hex_to_int(i_hex text, OUT o_dec integer)
RETURNS integer LANGUAGE 'plpgsql' IMMUTABLE STRICT AS $$
BEGIN
    EXECUTE 'SELECT x''' || i_hex || '''::integer' INTO o_dec;
    RETURN;
END $$;

SELECT
    client_addr,
    sent_offset - (
        replay_offset - (sent_xlog - replay_xlog) * 255 * 16 ^ 6 ) AS byte_lag
FROM (
    SELECT
        client_addr,
        hex_to_int(split_part(sent_location, '/', 1)) AS sent_xlog,
        hex_to_int(split_part(replay_location, '/', 1)) AS replay_xlog,
        hex_to_int(split_part(sent_location, '/', 2)) AS sent_offset,
        hex_to_int(split_part(replay_location, '/', 2)) AS replay_offset
    FROM pg_stat_replication
) AS s;

--
Kind regards,
Sergey Konoplev
PostgreSQL Consultant and DBA

http://www.linkedin.com/in/grayhemp
+1 (415) 867-9984, +7 (901) 903-0499, +7 (988) 888-1979
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