| From: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
|---|---|
| To: | Nikhil Sontakke <nikhils(at)2ndquadrant(dot)com> |
| Cc: | Stas Kelvich <s(dot)kelvich(at)postgrespro(dot)ru>, Simon Riggs <simon(at)2ndquadrant(dot)com>, PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org>, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com> |
| Subject: | Re: Speedup twophase transactions |
| Date: | 2017-01-31 05:38:15 |
| Message-ID: | CAB7nPqR3fLPsBVAQ_dGPb1VvPEv2mFU4j+eyJrYSMNuAVoFDvA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jan 31, 2017 at 2:34 PM, Nikhil Sontakke
<nikhils(at)2ndquadrant(dot)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
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