| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Siddharth Kothari <sidkot(at)google(dot)com> |
| Cc: | pgsql-bugs(at)lists(dot)postgresql(dot)org, Vaibhav Jain <jainva(at)google(dot)com>, Madhukar <madhukarprasad(at)google(dot)com>, Xun Cheng <xuncheng(at)google(dot)com> |
| Subject: | Re: Fix size estimation for parallel B-Tree scans with skip arrays |
| Date: | 2026-04-29 14:43:47 |
| Message-ID: | CAH2-Wzk6-mzP4utr9=sKT9XQi+NgonD_X30z1sf_hgnKQvPpGg@mail.gmail.com |
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| Lists: | pgsql-bugs |
On Wed, Apr 29, 2026 at 2:54 AM Siddharth Kothari <sidkot(at)google(dot)com> wrote:
> Root cause:
>
> In src/backend/access/nbtree/nbtree.c, the loop in btestimateparallelscan assumes that every index column might require a skip array and adds sizeof(int) to the estimated size:
>
> However, every skip array actually needs space for its slot in the btps_arrElems array AND space to store its scan key's sk_flags.
Your diagnosis looks correct to me. As you said, the problem is that
we only add btps_arrElems space overhead for input scan keys -- we
neglect to do the same for any skip array scan key that might be
output by nbtree preprocessing later on.
I'll commit this patch later today.
Thanks!
--
Peter Geoghegan
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