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From: Siddharth Kothari <[email protected]>
To: Peter Geoghegan <[email protected]>
Cc: [email protected]
Cc: Vaibhav Jain <[email protected]>
Cc: Madhukar <[email protected]>
Cc: Xun Cheng <[email protected]>
Subject: Re: Fix size estimation for parallel B-Tree scans with skip arrays
Date: Wed, 29 Apr 2026 20:29:23 +0530
Message-ID: <CAGCUe0L+M113dXmW44LWDmqSHa8kMcwAKgW+hXdTwVd-8dz8jA@mail.gmail.com> (raw)
In-Reply-To: <CAH2-Wzk6-mzP4utr9=sKT9XQi+NgonD_X30z1sf_hgnKQvPpGg@mail.gmail.com>
References: <CAGCUe0Lwk3C0qdkBa+OLpYc7yXwW=pbaz8Sju4xMXEQAmyp+5g@mail.gmail.com>
	<CAH2-Wzk6-mzP4utr9=sKT9XQi+NgonD_X30z1sf_hgnKQvPpGg@mail.gmail.com>

Thank you Peter!

On Wed, Apr 29, 2026 at 8:14 PM Peter Geoghegan <[email protected]> wrote:

> On Wed, Apr 29, 2026 at 2:54 AM Siddharth Kothari <[email protected]>
> 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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