Hi, Thanks for looking into this.
On Mon, Sep 16, 2024 at 4:54 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > Why raise the ERROR just for timeout invalidation here and why not if > the slot is invalidated for other reasons? This raises the question of > what happens before this patch if the invalid slot is used from places > where we call ReplicationSlotAcquire(). I did a brief code analysis > and found that for StartLogicalReplication(), even if the error won't > occur in ReplicationSlotAcquire(), it would have been caught in > CreateDecodingContext(). I think that is where we should also add this > new error. Similarly, pg_logical_slot_get_changes_guts() and other > logical replication functions should be calling > CreateDecodingContext() which can raise the new ERROR. I am not sure > about how the invalid slots are handled during physical replication, > please check the behavior of that before this patch. When physical slots are invalidated due to wal_removed reason, the failure happens at a much later point for the streaming standbys while reading the requested WAL files like the following: 2024-09-16 16:29:52.416 UTC [876059] FATAL: could not receive data from WAL stream: ERROR: requested WAL segment 000000010000000000000005 has already been removed 2024-09-16 16:29:52.416 UTC [872418] LOG: waiting for WAL to become available at 0/5002000 At this point, despite the slot being invalidated, its wal_status can still come back to 'unreserved' even from 'lost', and the standby can catch up if removed WAL files are copied either by manually or by a tool/script to the primary's pg_wal directory. IOW, the physical slots invalidated due to wal_removed are *somehow* recoverable unlike the logical slots. IIUC, the invalidation of a slot implies that it is not guaranteed to hold any resources like WAL and XMINs. Does it also imply that the slot must be unusable? -- Bharath Rupireddy PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
