On Mon, Sep 30, 2013 at 10:50 AM, Andres Freund <and...@2ndquadrant.com> wrote: > Changeset extraction only works in the context of a single database but > has to scan through xlog records from multiple databases. Most records > are easy to skip because they contain the database in the relfilenode or > are just not interesting for logical replication. The only exception are > compact commits. > So we have some alternatives: > 1) don't do anything, in that case empty transactions will get replayed since > the changes > themselves will get skipped. > 2) Don't use compact commits if wal_level=logical > 3) unify compact and non-compact commits, trying to get the normal one > smaller. > > For 3) I am thinking of using 'xinfo' to store whether we have the other > information or not. E.g. if there are subxacts in a compact commit we > signal that by the flag 'XACT_COMMIT_CONTAINS_SUBXACTS' and store the > number of subxacts after the xlog record. Similarly with relations, > invalidation messages and the database id. That should leave compact > commits without any subxacts at the former size, and those with at the > former size + 4. Normal commits would get smaller in many cases since we > don't store the empty fields. > > I personally think 3) is the best solution, any other opinions?
What's wrong with #1? -- 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
