Re: [HACKERS] Notice: heap_open/close changes committed

Vadim Mikheev <vadim(at)krs(dot)ru> writes:
> Tom Lane wrote:
>> 2. I made most opens of system relations grab AccessShareLock if
>> read-only, or RowExclusiveLock if read-write, on the theory that
> ^^^^^^^^^^^^^^^^

> There are problems here. In the case of normal UPDATE/DELETE
> (when RowExclusiveLock is acquired) Executor takes care about
> the-same-row writers, but other parts of system don't check
> is tuple read being updated concurrent transaction or not.

Drat. I was afraid I might be getting in over my head :-(

> This is the old bug (pre-6.5.X released WRITE lock just after
> system table was modified). I had no time to fix it and so
> just changed old WRITE lock with new AccessExclusiveLock.

I do not think changing RowExclusiveLock back to AccessExclusiveLock
will fix it unless we hold the lock till end of transaction, no?
That seems like much too high a price to pay.

> But we have to handle this in proper way (wait if t_xmax
> is id of an active transaction).

Yes. Where is the code that does this right in the regular executor?
I will see what needs to be done to make the system table accesses
act the same.

regards, tom lane