Hi, On 2023-11-17 15:39:14 -0300, Euler Taveira wrote: > On Mon, Nov 13, 2023, at 9:47 PM, Bruce Momjian wrote: > > Is this documentation change still relevant? > > I think so. AFAICS nothing changed. Unless you read the source code, it is not > clear that VACUUM removes the information for frozen tuples. They are > decoupled > (but executed in the same routine for convenience), hence, someone can ask why > the pg_xact_commit_timestamp() returns NULL for a transaction that was > executed > *after* you enable track_commit_timestamp.
I think the connection between freezing and removal of commit timestamps is a lot less direct that your suggested docs suggest. There can be no freezing and we'll still remove timestamps (if tuples were deleted/updated). And tuples can be frozen without the committs being truncated (if other tables have an older relfrozenxid). The relevant limiting factor is minimum of all databases datfrozenxid. Which in turn is limited by relfrozenxid of each table in said database. And relfrozenxid is limited by snapshots (and prepared transactions, replication slots, etc). > The answer is the design used a existing mechanism to clean up data in order > to avoid creating a new one. I don't really understand this part - independent of the mechanism (i.e. an slru), at some point we need to remove old data, just for space reasons. Greetings, Andres Freund
