On Fri, Feb 13, 2026 at 07:46:22AM +0000, PG Bug reporting form wrote:
> After upgrading from PostgreSQL 15.15 to 15.16, substring(text) raises:
> >ERROR: invalid byte sequence for encoding "UTF8": 0xe6 0x97
> on valid UTF-8 text stored in a TOAST-compressed column.
> user=> select substring(data from 1 for 1) from toast_repro;
> ERROR: 22021: invalid byte sequence for encoding "UTF8": 0xe6 0x97
Thanks for the report. That is a bug and a regression; I regret missing it
during review. The substring operation works by taking a 4-byte slice from
the toasted value (4 bytes being the max length of a UTF8 char in PostgreSQL),
the finding the actual first character within those bytes. However, it
incorrectly requires those four bytes to be a valid UTF8 string. I'll start
on a fix.
