Обсуждение: RS_EPHEMERAL vs RS_TEMPORARY
I'm trying to figure out what's specific about RS_EPHEMERAL and RS_TEMPORARY slot kinds. The following comment (see definition of the ReplicationSlotPersistency enumeration) tells when each kind is dropped * Slots marked as PERSISTENT are crash-safe and will not be dropped when * released. Slots marked as EPHEMERAL will be dropped when released or after * restarts. Slots marked TEMPORARY will be dropped at the end of a session * or on error. ... typedef enum ReplicationSlotPersistency However I don't see the actual difference: whenever ReplicationSlotCleanup() is called (on error or session end), ReplicationSlotRelease() has already been called too. And as for server restart, I see that RestoreSlotFromDisk() discards both EPHEMERAL and TEMPORARY. Do we really need both of them? -- Antonin Houska Web: https://www.cybertec-postgresql.com
On 2020-02-25 08:30, Antonin Houska wrote: > I'm trying to figure out what's specific about RS_EPHEMERAL and RS_TEMPORARY > slot kinds. The following comment (see definition of the > ReplicationSlotPersistency enumeration) tells when each kind is dropped The general idea is that an "ephemeral" slot is a future persistent slot that is not completely initialized yet. If there is a crash and you find an ephemeral slot, you can clean it up. The name is perhaps a bit odd, you can think of it as an uninitialized one. A temporary slot is one that behaves like a temporary table: It is removed at the end of a session. Perhaps the implementation differences are not big or are none, but it's relevant for reporting. For example, the pg_replication_slots view shows which slots are temporary. You wouldn't want to show an ephemeral slot as temporary. -- Peter Eisentraut http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Peter Eisentraut <peter.eisentraut@2ndquadrant.com> wrote: > On 2020-02-25 08:30, Antonin Houska wrote: > > I'm trying to figure out what's specific about RS_EPHEMERAL and RS_TEMPORARY > > slot kinds. The following comment (see definition of the > > ReplicationSlotPersistency enumeration) tells when each kind is dropped > > The general idea is that an "ephemeral" slot is a future persistent slot that > is not completely initialized yet. If there is a crash and you find an > ephemeral slot, you can clean it up. The name is perhaps a bit odd, you can > think of it as an uninitialized one. A temporary slot is one that behaves > like a temporary table: It is removed at the end of a session. > > Perhaps the implementation differences are not big or are none, but it's > relevant for reporting. For example, the pg_replication_slots view shows > which slots are temporary. You wouldn't want to show an ephemeral slot as > temporary. ok, so only comments seem to be the problem. Anyway, the reason I started to think about it was that I noticed an Assert() statement I considered inaccurate. Does this patch make sense? -- Antonin Houska Web: https://www.cybertec-postgresql.com