Re: [PROPOSAL] Backup and recovery of pg_statistic

> There's still the problem that it won't work across a major version
> upgrade that makes any change whatsoever to the rowtype of pg_statistic.

I'm sorry if my previous explanation was poor, this time I am going to be 
detailed.

Suppose you want to upgrade from 9.4 to 9.6. In that case you would use the 
pg_upgrade utility provided by the release 9.6, which means that it's the 
pg_dump who would have to connect to the older instance and to prepare tuples 
to be inserted to the pg_statistic of the newer instance. The pg_dump utility 
would have to convert statistical data to the new format (for example, add 
placeholders for new columns), so generated INSERT statements would be fine 
provided that the pg_dump would be up-to-date.

The documentation states that we should always run the pg_upgrade binary of 
the new server, not the old one [http://www.postgresql.org/docs/9.5/static/
pgupgrade.html, Usage, #9]. This means that the pg_upgrade will definitely use 
a fresh version of pg_dump utility that is aware of all possible pitfalls.

Furthermore, each INSERT statement consists of textually-serialized columns of 
pg_statistic. Columns of 'anyarray' type are deserialized using the 'array_in' 
procedure which performs various sanity checks, including the element type 
check. Thus it is not possible to insert an anyarray object which will cause 
server death.


-- 
Dmitry Ivanov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company