Hello, We are currently testing Synchronous Streaming replication between two PG 9.1 boxes () in a test environment, with the slave as hot_standby. We appear to have it working correctly (changes appear on both) etc
However the following query from ( http://www.dansketcher.com/2013/01/27/monitoring-postgresql-streaming-replication/ ): SELECT client_addr, sent_offset - (replay_offset - (sent_xlog - replay_xlog) * 255 * 16 ^ 6 ) AS byte_lag FROM ( SELECT client_addr, ('x' || lpad(split_part(sent_location, '/', 1), 8, '0'))::bit(32)::bigint AS sent_xlog, ('x' || lpad(split_part(replay_location, '/', 1), 8, '0'))::bit(32)::bigint AS replay_xlog, ('x' || lpad(split_part(sent_location, '/', 2), 8, '0'))::bit(32)::bigint AS sent_offset, ('x' || lpad(split_part(replay_location, '/', 2), 8, '0'))::bit(32)::bigint AS replay_offset FROM pg_stat_replication ) AS s; the byte_lag is almost never 0 and usually 816 bytes. Similiarly, the output from pg_stat_replication *very* rarely has write_location and replay_location the same. procpid | usesysid | usename | application_name | client_addr | client_hostname | client_port | backend_start | state | sent_location | write_location | flush_location | replay_location | sync_priority | sync_state ---------+----------+-------------+------------------+-------------+-----------------+-------------+------------------------------+-----------+---------------+----------------+----------------+-----------------+---------------+------------ 17895 | 7141183 | replication | walreceiver | 10.2.1.151 | | 58017 | 2014-04-04 12:41:16.36911+01 | streaming | 17/E6014228 | 17/E6014228 | 17/E6014228 | 17/E6013F08 | 1 | sync (1 row) I've been attempting to find documentation about the meaning of sent_location, write_location, flush_location and replay_location but have so far been unsuccessful; especially with regards to the implications of replay_location being < flush_location. Is this "normal" for synchronous replication? Many Thanks, Rob
