Michael Paquier wrote: > That’s actually what pg_rman is doing for what it calls incremental > backups (perhaps that would be differential backup in PG > terminology?), and the performance is bad as you can imagine. We could > have a dedicated LSN map to do such things with 4 bytes per page. I am > still not convinced that this much facility and the potential bug > risks are worth it though, Postgres already knows about differential > backups if you shape it as a delta of WAL segments. I think that, in > order to find a LSN map more convincing, we should find first other > use cases where it could become useful. Some use cases may pop up with > VACUUM, but I have not studied the question hard enough...
The case I've discussed with barman developers is a large database (couple dozen of TBs should be enough) where a large fraction (say 95%) is read-only but there are many changes to the active part of the data, so that WAL is more massive than size of active data. -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers