On Fri, 2020-05-22 at 12:48 -0400, Rui DeSousa wrote: > > On May 22, 2020, at 12:36 AM, Raj kumar <rajkumar820999@xxxxxxxxx> wrote: > > > > . But, ideally for sync replication, lag should be always 0 right. > > Incorrect. Synchronous replication means that a commit will not return until it has been safely written to disk on the primary and the replica. That means the transaction is written to WAL file on > both primary and replica. On the primary, the transaction is also visible to transactions with a later xmin. On the replica, the transaction has been recorded in the WAL; it still needs to get > applied to the database for it to become visible to read transactions. If you set "synchronous_commit = remote_apply", the commit will only return when the change has been replayed on the synchronous standby server. Yours, Laurenz Albe -- Cybertec | https://www.cybertec-postgresql.com
