| From: | Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
| Cc: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Amit Langote <amitlangote09(at)gmail(dot)com>, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>, Rajkumar Raghuwanshi <rajkumar(dot)raghuwanshi(at)enterprisedb(dot)com>, Beena Emerson <memissemerson(at)gmail(dot)com>, amul sul <sulamul(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Dilip Kumar <dilipbalaut(at)gmail(dot)com> |
| Subject: | Re: [HACKERS] Runtime Partition Pruning |
| Date: | 2018-04-13 05:38:46 |
| Message-ID: | 0b361a22-f995-e15c-a385-6d1b72dd0d13@lab.ntt.co.jp |
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| Lists: | pgsql-hackers |
On 2018/04/13 1:57, Robert Haas wrote:
>> It might be possible to do something better in each module by keeping
>> an array indexed by RTI which have each entry NULL initially then on
>> first relation_open set the element in the array to that pointer.
>
> I'm not sure that makes a lot of sense in the planner, but in the
> executor it might be a good idea. See also
> https://www.postgresql.org/message-id/CA%2BTgmoYKToP4-adCFFRNrO21OGuH%3Dphx-fiB1dYoqksNYX6YHQ%40mail.gmail.com
> for related discussion. I think that a coding pattern where we rely
> on relation_open(..., NoLock) is inherently dangerous -- it's too easy
> to be wrong about whether the lock is sure to have been taken. It
> would be much better to open the relation once and hold onto the
> pointer, not just for performance reasons, but for robustness.
About the specific relation_open(.., NoLock) under question, I think there
might be a way to address this by opening the tables with the appropriate
lock mode in partitioned_rels list in ExecLockNonleafAppendTables and
keeping the Relation pointers around until ExecEndNode. Then instead of
ExecSetupPartitionPruneState doing relation_open/close(.., NoLock), it
just reuses the one that's passed by the caller.
Attached a PoC patch. David, thoughts?
Thanks,
Amit
| Attachment | Content-Type | Size |
|---|---|---|
| open-partitioned-rels-for-pruning-1.patch | text/plain | 10.0 KB |
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