Re: Online base backup from the hot-standby

2011/8/5 Jun Ishiduka <ishizuka(dot)jun(at)po(dot)ntts(dot)co(dot)jp>:
> * Procedure
>
> 1. Call pg_start_backup('x') on the standby.
> 2. Take a backup of the data dir.
> 3. Call pg_stop_backup() on the standby.
> 4. Copy the control file on the standby to the backup.
> 5. Check whether the control file is status during hot standby with pg_controldata.
>   -> If the standby promote between 3. and 4., the backup can not recovery.
>      -> pg_control is that "Minimum recovery ending location" is equals 0/0.
>      -> backup-end record is not written.

What if we do #4 before #3? The backup gets corrupted? My guess is
that the backup is still valid even if we copy pg_control before executing
pg_stop_backup(). Which would not require #5 because if the standby
promotion happens before pg_stop_backup(), pg_stop_backup() can
detect that status change and cancel the backup.

#5 looks fragile. If we can get rid of it, the procedure becomes more
robust, I think.

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center