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Re: Hash-based MCV matching for large IN-lists

Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>

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From: Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>
To: Chengpeng Yan <chengpeng_yan@Outlook.com>
Cc: David Geier <geidav.pg@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2026-01-29T11:14:43Z
Lists: pgsql-hackers

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Hi Chengpeng,

Thanks for your review!


On 28.01.2026 16:08, Chengpeng Yan wrote:
> * Treat NULL array elements as zero selectivity for ALL:

Agreed. For ALL/AND semantics the function now returns selectivity = 0.0 
as soon as a NULL element is encountered.


> * Fix cross-type equality argument order in `mcvs_in_equal`:

Agreed. Added 'op_is_reserved' flag MCVInHashContext, same as in 
MCVHashContext.


> * Include non-MCV IN-list constants in non-disjoint selectivity:

This is not applicable to v3.


> * Avoid double-negating inequality estimates for non-Const elements:

Agreed. var_eq_non_const() is now always with negate = false, not to 
call negation twice.


Attached v4 patch with above fixes.

-- 
Best regards,
Ilia Evdokimov,
Tantor Labs LLC,
https://tantorlabs.com/

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Short-circuit row estimation in NOT IN containing NULL consts