Re: Recovery control functions

On Fri, Jan 14, 2011 at 8:15 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On Fri, 2011-01-14 at 11:09 +0000, Simon Riggs wrote:
>> Functions to control recovery, to aid PITR and Hot Standby.
>> pg_is_xlog_replay_paused()
>> pg_xlog_replay_pause()
>> pg_xlog_replay_resume()
>>
>> recovery.conf parameter: pause_at_recovery_target (bool)
>
> And now with the correct patch.

IIRC, in last year, you implemented the related function which
advances recovery the specified number of records and pauses.
Why did you drop that from the patch? That's very useful at least
for me to do PITR and debug the recovery code.

+ If in hot standby, all queries will see the same consistent snapshot
+ of the database, and no query conflicts will be generated.

Really? The access exclusive lock taken from the master before
pause of recovery can conflict with a query?

+ <primary><varname>pause_at_recovery_target</> recovery
parameter</primary>
+ </indexterm>
+ <listitem>
+ <para>
+ Specifies whether recovery should pause when the recovery target
+ is reached. The default is true, if a recovery target is set.

The default is false, according to the code.

If HS is disabled and pause_at_recovery_target is enabled,
recovery might never end infinitely. This is not desirable.
We should reject such a combination of settings or emit
WARNING?

+ while (RecoveryIsPaused());
+ {
+ pg_usleep(100000L); /* 100 ms */
+ HandleStartupProcInterrupts();

100ms seems too short. What about 1s or bigger?
Or wait on the latch rather than using poll loop.

Regards,

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