On 12/18/2013 01:39 PM, Andres Freund wrote:
On 2013-12-18 13:07:51 +0200, Heikki Linnakangas wrote:
Here's another idea that doesn't involve SSI:

At COMMIT, take a new snapshot and check that the assertion still passes
with that snapshot. Now, there's a race condition, if another transaction is
committing at the same time, and performs the same check concurrently. That
race condition can be eliminated by holding an exclusive lock while running
the assertion, until commit, effectively allowing the assertion to be
checked by only one transaction at a time.

I think that would work, and would be simple, although it wouldn't scale too

It probably would also be very prone to deadlocks.

Hmm, since this would happen at commit, you would know all the assertions that need to be checked at that point. You could check them e.g in Oid order to avoid deadlocks.

- Heikki

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