Re: [HACKERS] Speedup twophase transactions

On Tue, Jan 31, 2017 at 2:34 PM, Nikhil Sontakke
<nikhils@2ndquadrant.com> wrote:
>>> I wonder what's the best location for this in the common case when we
>>> do shutdown of standby.  We could add code in XLOG_CHECKPOINT_SHUTDOWN
>>> and XLOG_CHECKPOINT_ONLINE xlog_redo code path.
>>
>> ShutdownXLOG() calls CreateRestartPoint() when a standby shuts down,
>> so doing all the durability work in CheckPointTwoPhase() would take
>> care of any problems.
>>
>
> ShutdownXLOG() gets called from the checkpointer process. See comments
> above about the checkpointer not having access to the proper
> KnownPreparedList.
>
> The following test sequence will trigger the issue:
>
> 1) start master
> 2) start replica
> 3) prepare a transaction on master
> 4) shutdown master
> 5) shutdown replica
>
> CheckPointTwoPhase() in (5) does not sync this prepared transaction
> because the checkpointer's KnownPreparedList is empty.

And that's why this needs to be stored in shared memory with a number
of elements made of max_prepared_xacts...
-- 
Michael