We have a master/slave setup with replication. Today we failed over to the slave and saw disk I/O go through the roof.
Are the pg_statistic statistics synced along with streaming replication? Are you expected to have to do a vacuum analyze after failing over? That's what we're trying now to see if it makes a difference. Our next step will be to fall back to the first host and see where this one went wrong (society? lax discipline at home? the wrong sort of friends?)