Re: Optimize planner memory consumption for huge arrays

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>
Cc: Lepikhov Andrei <a(dot)lepikhov(at)postgrespro(dot)ru>, Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org, Евгений Бредня <e(dot)brednya(at)postgrespro(dot)ru>
Subject: Re: Optimize planner memory consumption for huge arrays
Date: 2024-02-19 21:51:47
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Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> writes:
> On 2/19/24 16:45, Tom Lane wrote:
>> Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> writes:
>>> For example, I don't think we expect selectivity functions to allocate
>>> long-lived objects, right? So maybe we could run them in a dedicated
>>> memory context, and reset it aggressively (after each call).

>> That could eliminate a whole lot of potential leaks. I'm not sure
>> though how much it moves the needle in terms of overall planner
>> memory consumption.

> I'm not sure about that either, maybe not much - for example it would
> not help with the two other memory usage patches (which are related to
> SpecialJoinInfo and RestrictInfo, outside selectivity functions).

> It was an ad hoc thought, inspired by the issue at hand. Maybe it would
> be possible to find similar "boundaries" in other parts of the planner.

Here's a quick and probably-incomplete implementation of that idea.
I've not tried to study its effects on memory consumption, just made
sure it passes check-world.

The main hazard here is that something invoked inside clause
selectivity might try to cache a data structure for later use.
However, there are already places that do that kind of thing,
and they already explicitly switch into the planner_cxt, because
otherwise they fail under GEQO. (If we do find places that need
fixing for this, they were probably busted under GEQO already.)
Perhaps it's worth updating the comments at those places, but
I didn't bother in this first cut.

regards, tom lane

Attachment Content-Type Size
v1-estimate-selectivities-in-temp-context.patch text/x-diff 5.7 KB

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