| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Tomas Vondra <tomas(at)vondra(dot)me> |
| Cc: | Mark Dilger <mark(dot)dilger(at)enterprisedb(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, pgsql-hackers(at)lists(dot)postgresql(dot)org, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com> |
| Subject: | Re: Adding skip scan (including MDAM style range skip scan) to nbtree |
| Date: | 2025-05-09 17:22:33 |
| Message-ID: | CAH2-WzmhSe0u1R8xF75Asam6U3t01ZdEE1z7R0C3UMKiUiSTZQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, May 9, 2025 at 1:19 PM Tomas Vondra <tomas(at)vondra(dot)me> wrote:
> Not sure I understand. Why would it need to scan 85 index pages? There's
> only 100 matching tuples total, spread over the 100 partitions. We'll
> need to scan maybe 1 page per partition.
I was unclear. The thing about 85 leaf pages only applies when
partitioning isn't in use. When it is in use, each individual
partition's index has only one index leaf page. So each individual
index scan is indeed fairly inexpensive, particularly relative to
startup cost/preprocessing cost.
--
Peter Geoghegan
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