From: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
---|---|
To: | Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Cc: | David Rowley <dgrowley(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com> |
Subject: | EXPLAIN IndexOnlyScan shows disabled when enable_indexonlyscan=on |
Date: | 2024-10-22 00:45:32 |
Message-ID: | CAAKRu_atV=kovgpaLREyG68PB5+ncKvJ2UNoeRetEgyC3Yb5Sw@mail.gmail.com |
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I was surprised today when I saw that with
enable_indexscan=off
enable_indexonlyscan=on
EXPLAIN prints that the index only scan is disabled:
QUERY PLAN
-----------------------------------------------
Index Only Scan using history_pkey on history
Disabled: true
I wasn't sure if this was expected -- maybe index-only scan is
considered a type of index scan for this purpose. I dug around this
disable_cost thread [1] a bit to see if I could figure out what the
expected behavior is on my own, but I'm still not sure.
Anyway, maybe I'm misunderstanding something.
Here's my repro:
CREATE TABLE history(
id INT PRIMARY KEY GENERATED BY DEFAULT AS IDENTITY,
data TEXT);
INSERT INTO history(data)
select repeat('a', 100) from generate_series(1,10000)i;
VACUUM history;
set enable_seqscan = off;
set enable_indexscan = off;
set enable_bitmapscan = off;
set enable_indexonlyscan = on;
EXPLAIN (costs off) SELECT id from history;
- Melanie
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