On Sat, Nov 8, 2014 at 5:35 AM, Petr Jelinek <p...@2ndquadrant.com> wrote: > That's not what I said. I am actually ok with adding the LSN if people see > it useful. > I was just wondering if we can make the record smaller somehow - 24bytes per > txid is around 96GB of data for whole txid range and won't work with pages > smaller than ~4kBs unless we add 6 char support to SLRU (which is not hard > and we could also not allow track_commit_timestamps to be turned on with > smaller pagesize...). > > I remember somebody was worried about this already during the original patch > submission and it can't be completely ignored in the discussion about adding > more stuff into the record.
Fair point. Sorry I misunderstood. I think the key question here is the time for which the data needs to be retained. 2^32 of anything is a lot, but why keep around that number of records rather than more (after all, we have epochs to distinguish one use of a given txid from another) or fewer? Obvious alternatives include: - Keep the data for some period of time; discard the data when it's older than some threshold. - Keep a certain amount of total data; every time we create a new file, discard the oldest one. - Let consumers of the data say how much they need, and throw away data when it's no longer needed by the oldest consumer. - Some combination of the above. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
