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help / color / mirror / Atom feedFrom: Mark Frost <[email protected]>
To: [email protected] <[email protected]>
Subject: RE: Poor row estimates from planner, stat `most_common_elems` sometimes missing for a text[] column
Date: Fri, 6 Jun 2025 09:21:34 +0000
Message-ID: <PH3PPF1C905D6E61EEB89CF46C1F572D402E16EA@PH3PPF1C905D6E6.namprd15.prod.outlook.com> (raw)
In-Reply-To: <[email protected]>
References: <PH3PPF1C905D6E6F24A5C1A1A1D8345B593E16FA@PH3PPF1C905D6E6.namprd15.prod.outlook.com>
<[email protected]>
> On 6/5/25 17:42, Mark Frost wrote:
> > Is there any good explanation for this behaviour? Preferably we’d like
> > some way for proper `most_common_elems` statistics to be collected in
> > our production database, in the hope that influences a good query plan
> > to always be selected.
> most_common_elems has a limited size, and if all the elements have the
> same freq, there's nothing we can do.
> You could do: alter table test alter column tags set statistics X;
> However, X is capped at 10000…
Actually *any* most_common_elems stats would be fine, because the reasoning is:
* If the searched element is in most_common_elems we know it’s frequency
* If it’s not, it’s less frequent than the least most_common_elems
So in our case when every row is unique, we’d only actually need stats to record a single most_common_elems (if only it would record one)
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Subject: RE: Poor row estimates from planner, stat `most_common_elems` sometimes missing for a text[] column
In-Reply-To: <PH3PPF1C905D6E61EEB89CF46C1F572D402E16EA@PH3PPF1C905D6E6.namprd15.prod.outlook.com>
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