Re: Apply worker can pick an invalid index for REPLICA IDENTITY FULL lookups

On Sun, 23 Aug 2026 at 01:26, Mihail Nikalayeu
<mihailnikalayeu(at)gmail(dot)com> wrote:
>
> Hello,
>
> When the remote relation has REPLICA IDENTITY FULL and the local one
> has no primary key or replica identity, the apply worker looks for any
> index it can search by.
> FindUsableIndexForReplicaIdentityFull() walks RelationGetIndexList()
> and takes the first index of a suitable shape without checking if it
> is valid.
> That list omits only indexes that are not indislive, so the leftover
> from a failed CREATE INDEX CONCURRENTLY is eligible -- and such an
> index need not contain every row.
>
> A failed CIC validation leaves an index that scans cleanly but lacks
> exactly the rows validation would have added. Consequently, updates
> and deletes for those rows are dropped as update_missing conflicts and
> the subscriber quietly diverges.
>
> A failed build leaves an index that is empty down to the metapage,
> which parks the subscription in a permanent error:
> ERROR: could not read blocks 0..0 in file "base/5/16433": read only 0
> of 8192 bytes
>
> The fix and a reproducer are in the attachments.
>
> Affects 16 and up, from 89e46da5e51.

Thanks for the patch, the patch does not apply on PG17 version, you
might have to provide a separate patch for PG17 & below version:
patch -p1 < v1-0001-Don-t-choose-an-invalid-index-for-REPLICA-IDENTIT.patch
patching file 'src/backend/replication/logical/relation.c'
1 out of 1 hunks failed--saving rejects to
'src/backend/replication/logical/relation.c.rej'
patching file 'src/test/subscription/t/032_subscribe_use_index.pl'

Regards,
Vignesh