Re: Parallel Sort

Hannu Krosing <hannu(at)krosing(dot)net> writes:
> Has anybody looked into making syscache MVCC compliant ?

This is the wrong statement of the question.

The right statement is "how would you like backend A to be updating
table T in compliance with a view of table T's schema that is obsolete
because of backend B's already-committed DDL changes?" For example,
ignoring a just-committed CHECK constraint because it's not visible
to your transaction's snapshot.

The point of SnapshotNow catalog lookups is to be sure that we see the
current definition of a table whether or not we're in a transaction
whose snapshot precedes the last DDL change to that table. There might
be some other way to deal with that consistency problem, but just
changing syscache's behavior is not going to make things better.

regards, tom lane