On 18 April 2016 at 12:11, David Rowley <david.row...@2ndquadrant.com>

> this is not helping me much as I don't really understand why
> pg_statistic need to be frozen?

Yeah, in particular it's not clear to me why pg_upgrade goes to such
efforts to freeze everything when it copies pg_clog over in
copy_clog_xlog_xid() .

Is it mainly a defense against the multixact format change?

 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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