I'd been wondering why a VACUUM FREEZE is performed during pg_upgrade,
so I opened up the code to see if that would help me determine why
this is.
I'm confronted with a comment, which states;
/*
* We do freeze after analyze so pg_statistic is also frozen. template0 is
* not frozen here, but data rows were frozen by initdb, and we set its
* datfrozenxid, relfrozenxids, and relminmxid later to match the new xid
* counter later.
*/
this is not helping me much as I don't really understand why
pg_statistic need to be frozen?
-- David Rowley http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services