Re: [BUG] false positive in bt_index_check in case of short 4B varlena datum

> On 2 May 2026, at 00:41, Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> This is checking (as you noted) !VARATT_IS_EXTENDED, whereas the
> bt_normalize_tuple() code is checking !VARATT_IS_COMPRESSED.
>
> VARATT_IS_EXTENDED() will return true for short varlenas (because it's not a
> standard 4 byte uncompressed varlena), whereas VARATT_IS_COMPRESSED() will
> return false for a short varlena (since it's not compressed).
>
> I didn't find other instanes of similar code that uses !VARATT_IS_COMPRESSED.

As far as I understand

!VARATT_IS_COMPRESSED(DatumGetPointer(normalized[i])) && !VARATT_IS_SHORT(DatumGetPointer(normalized[i]))

is exactly

!VARATT_IS_EXTENDED(DatumGetPointer(untoasted_values[i]))

Which is what was proposed in v2 patch. But later was changed to !VARATT_IS_COMPRESSED().
As I understood it was done to further strengthen normalization.

So the intent might be that short varatts need normalization in some cases. But we have no tests that show such a case.
I tried to build a problematic storage alternation like [0], but everything works nicely.

So I propose something in a line with attached patch.

Best regards, Andrey Borodin.

[0] https://github.com/postgres/postgres/blob/master/contrib/amcheck/sql/check_btree.sql#L170-L172