On 3/18/23 06:35, Amit Kapila wrote: > On Sat, Mar 18, 2023 at 3:13 AM Tomas Vondra > <tomas.von...@enterprisedb.com> wrote: >> >> ... >> >> Clearly, for sequences we can't quite rely on snapshots/slots, we need >> to get the LSN to decide what changes to apply/skip from somewhere else. >> I wonder if we can just ignore the queued changes in tablesync, but I >> guess not - there can be queued increments after reading the sequence >> state, and we need to apply those. But maybe we could use the page LSN >> from the relfilenode - that should be the LSN of the last WAL record. >> >> Or maybe we could simply add pg_current_wal_insert_lsn() into the SQL we >> use to read the sequence state ... >> > > What if some Alter Sequence is performed before the copy starts and > after the copy is finished, the containing transaction rolled back? > Won't it copy something which shouldn't have been copied? >
That shouldn't be possible - the alter creates a new relfilenode and it's invisible until commit. So either it gets committed (and then replicated), or it remains invisible to the SELECT during sync. regards -- Tomas Vondra EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
