Alvaro, Michael, * Alvaro Herrera (alvhe...@alvh.no-ip.org) wrote: > 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.
Yes, we've seen environments like that also. Thanks! Stephen
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