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

Attachment: walsender_activity-20100618.patch
Description: Binary data

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