Kevin Grittner <kgrittn@ymail.com> writes:
> The Serializable Snapshot Isolation techniques only work on top of
> MVCC snapshot isolation. At the time of the SSI patch, catalogs
> were not accessed according to those rules, so we excluded them
> from SSI handling -- it just could not have worked in a meaningful
> way. (So catalog access is currently identical under REPEATABLE
> READ and SERIALIZABLE transaction isolation levels.)
Really? "SELECT * FROM pg_database" will ignore SSI?
I agree that the system's own catalog accesses don't pay attention
to SSI, and probably can't because of concerns about needing to see
fully up-to-date data. But that's not my question. My point is
that userland snapshots can be used to examine shared catalogs,
and even update them if you're a superuser.
regards, tom lane