On Mon, Feb 2, 2015 at 5:52 PM, Jim Nasby <jim.na...@bluetreble.com> wrote:
> On 2/2/15 7:36 PM, Jim Nasby wrote: > >> >>> Currently the fact that it needs to go back to old tables and FTS them >>> every 2B transactions (or rely on autovacuum for this) and you can't do >>> anything about it (like permanently freeze the tables) seems like a big >>> scalability issue. Does it not? >>> >> >> Unfortunately it's not terribly easy to fix this. The problem is if we >> try to play games here, we must have a 100% reliable method for changing >> relfrozenxid as soon as someone inserts a new tuple in the relation. It >> might be possible to tie this into the visibility map, but no one has >> looked at this yet. >> >> Perhaps you'd be willing to investigate this, or sponsor the work? >> > I'll see what I can do. Will talk to folks at pgDay in a month. > > Oh, there is another possibility that's been discussed: read-only tables. > If we had the ability to mark a table read-only, then a VACUUM FREEZE on > such a table would be able to set that table's relfrozenxid to > FrozenTransactionId and prevent any further attempts at vacuuming. This > might be easier than trying to do something automatic. > > I think if we could log "last update/delete/insert" timestamp for a table - we could use that to freeze tables that are not changed. I also wonder how pg_database.datfrozenxid is set? Is it equal to the oldest pg_class.relfrozenxid for that database? I ask because I am willing to give a try and update relfrozenxid for the tables that are never updated and frozen. Currently we are looking at 8-hour downtime to vacuum the whole db in single-user mode. High availability is more important that data loss in my case. [I still don't want to lose data, but it won't be the end of world if it happens]. Having read-only tables would be great. I was able to get great performance from unlogged tables, similarly read-only tables would be able to address issue with high-transactions and many large stale tables. > -- > Jim Nasby, Data Architect, Blue Treble Consulting > Data in Trouble? Get it in Treble! http://BlueTreble.com >
