From: | Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> |
---|---|
To: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
Cc: | Justin Pryzby <pryzby(at)telsasoft(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Should we add GUCs to allow partition pruning to be disabled? |
Date: | 2019-03-11 04:06:08 |
Message-ID: | 143b7b65-33fb-c5c3-bd4d-80d8b3d52c02@lab.ntt.co.jp |
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Lists: | pgsql-hackers |
On 2019/03/11 11:13, David Rowley wrote:
> On Mon, 11 Mar 2019 at 15:00, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> wrote:
>>
>> On Mon, 11 Mar 2019 at 14:33, Amit Langote
>> <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>>> PG 11 moved the needle a bit for SELECT queries:
>>>
>>> Excluding unnecessary partitions is slow for UPDATE and DELETE queries,
>>
>> With those words I expect the user might be surprised that it's still
>> slow after doing SET enable_partition_pruning = off;
>
> I had in mind in 10, 11 and master add a note to mention:
Thanks for putting this together.
> Currently, it is not recommended to have partition hierarchies more
> than a few hundred partitions. Larger partition hierarchies can
> suffer from slow planning times with <command>SELECT</command>
> queries. Planning times for <command>UPDATE</command> and
> <command>DELETE</command> commands may also suffer slow planning
> times, but in addition, memory consumption may also become an issue
> due to how the planner currently plans the query once per partition.
> These limitations are likely to be resolved in a future version of
> <productname>PostgreSQL</productname>.
How about slightly rewriting the sentence toward the end as:
memory consumption may also become an issue, because planner currently
plans the query once for every partition.
> I've not really thought too much on the fact that the issue also
> exists with inheritance tables in earlier version too.
That's fine maybe.
Thanks,
Amit
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