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Subject: Re: [BUG] false positive in bt_index_check in case of short 4B
 varlena datum
From: "Andrey M. Borodin" <x4mmm@yandex-team.ru>
In-Reply-To: <e6d20179-ddbd-3376-a7f5-4831df7d6b60@gmail.com>
Date: Mon, 8 Jan 2024 19:34:41 +0500
Cc: Michael Zhilin <m.zhilin@postgrespro.ru>,
 pgsql-bugs@postgresql.org,
 y sokolov <y.sokolov@postgrespro.ru>
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Message-Id: <49BBA065-4C9A-4E50-9048-B457907FF219@yandex-team.ru>
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 <e6d20179-ddbd-3376-a7f5-4831df7d6b60@gmail.com>
To: Alexander Lakhin <exclusion@gmail.com>
Archived-At: <https://www.postgresql.org/message-id/49BBA065-4C9A-4E50-9048-B457907FF219%40yandex-team.ru>
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Hi Alexander!

I think both cases are very interesting and deserve two separate bug =
items.

> On 14 Dec 2023, at 22:17, Alexander Lakhin <exclusion@gmail.com> =
wrote:
>=20
>=20
> By changing the storage mode for a column, you can also get another =
error:
> CREATE TABLE t(f1 text);
> CREATE INDEX t_idx ON t(f1);
> INSERT INTO t VALUES(repeat('1234567890', 1000));
> ALTER TABLE t ALTER COLUMN f1 SET STORAGE plain;
>=20
> CREATE EXTENSION amcheck;
> SELECT bt_index_check('t_idx', true);
>=20
> ERROR:  index row requires 10016 bytes, maximum size is 8191
>=20

I think In this case we should warn user that index contains tuples with =
datums that are not insertable anymore. And abort heapallindexed.


> On 8 Jan 2024, at 00:00, Alexander Lakhin <exclusion@gmail.com> wrote:
>=20
> What is your opinion regarding similar failures, which are not =
addressed
> by the patch? Besides the case shown above, there is another one:
> CREATE TABLE tbl(i int4, t text);
> ALTER TABLE tbl ALTER COLUMN t SET STORAGE plain;
> CREATE INDEX tbl_idx ON tbl (t, i) WITH (fillfactor =3D 10);
> INSERT INTO tbl SELECT g, repeat('Test', 250) FROM generate_series(1, =
130) g;
> ALTER TABLE tbl ALTER COLUMN t SET STORAGE extended;
>=20
> CREATE EXTENSION amcheck;
> SELECT bt_index_check('tbl_idx', true);
>=20
> ERROR:  heap tuple (0,1) from table "tbl" lacks matching index tuple =
within index "tbl_idx"
> HINT:  Retrying verification using the function =
bt_index_parent_check() might provide a more specific error.

IMO In this case we should handle VARATT_IS_EXTENDED in =
bt_normalize_tuple().

BTW CI fails of the original patch ITT are related to the fact that COPY =
in\out file is created in PG_ABS_SRCDIR instead of PG_ABS_BUILDDIR. In =
an off-list conversation I recommended Michael to mimic tests =
regress/largeobject.sql. Though, there might be better ideas.

Thanks!


Best regards, Andrey Borodin.=