Re: [PATCH] ANALYZE: hash-accelerate MCV tracking for equality-only types

On 22.01.2026 12:40, Chengpeng Yan wrote:

> The v2 patch is attached.

I took a deeper look at the v2 patch. The hash-based lookup itself looks 
correct, and when testing ANALYZE runtime with large 
default_statistics_target values, the patch indeed provides a noticeable 
speedup.

I have one small suggestion regarding the handling of firstcount1 and 
c1_cursor in the 'match' path.

When we find a match in track[], we increment count and perform 
bubble-up swaps to keep the array ordered by frequency. If the value 
previously has count = 1, it is effectively leaving the singleton (count 
= 1) region and becoming part of the count>1. Conceptually, this means 
that the boundary between these two regions (firstcount1) should move 
left by one.

Given that, it seems sufficient to update the boundary and then ensure 
that c1_cursor still point inside the singleton region:

if (was_count1 && j < firstcount1)
     firstcount1--;
if (c1_cursor < firstcount1)
     c1_cursor = firstcount1;

This avoids reasoning about specific shifted subranges 
(firstcount1..match_index). FIFO behavior is still preserved because 
c1_cursor is only advanced when an eviction actually happens.

Let me know if I'm overlooking any corner cases.

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