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From: Takahiro Itagaki on 17 Jun 2010 22:33
Hi,

We don't have any statistic views for walsenders in SR's master server
in 9.0, but such views would be useful to monitor and manage standby
servers from the master server. I have two ideas for the solution -
adding a new system view or recycling pg_stat_activity:

1. Add another system view for walsenders, ex. "pg_stat_replication".
It would show pid, remote host, and sent location for each walsender.

2. Make pg_stat_activity to show walsenders. We could use current_query
to display walsender-specific information, like:
=# SELECT * FROM my_stat_activity ;
-[ RECORD 1 ]----+---------------------------------
datid | 16384
<snip>
current_query | SELECT * FROM my_stat_activity ;
-[ RECORD 2 ]----+---------------------------------
datid | 0
datname |
procpid | 4300
usesysid | 10
usename | itagaki
application_name |
client_addr | ::1
client_port | 37710
backend_start | 2010-06-16 16:47:35.646486+09
xact_start |
query_start |
waiting | f
current_query | walsender: sent=0/701AAA8

The attached patch is a WIP codes for the case 2, but it might be
better to design management policy via SQL in 9.1 before such detailed
implementation. Comments welcome.

Regards,
---
Takahiro Itagaki
NTT Open Source Software Center
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