Re: Transactions and temp tables

Hi,

I am attaching a new patch that deals with the issue of the locks on
temporary tables that have been accessed in transactions that have been
prepared but not committed.
I have added another list that keeps track of temp tables accessed by
transactions that are prepared but not committed. The RemoveTempTable
callback does not try to acquire locks on these tables. Now postmaster
can terminate even with transactions in the prepared state that accessed
temp tables.

Let me know what you think.
manu

Tom Lane wrote:
> Emmanuel Cecchet <manu(at)frogthinker(dot)org> writes:
>
>> Ok, so actually I don't see any different behavior between a temp table
>> or a regular table. The locking happens the same way and as long as the
>> commit prepared happens (potentially in another session), the lock is
>> released at commit time which seems to make sense.
>>
>
> Right, the problem is that you can't shut down the original backend
> because it'll try to drop the temp table at exit, and then block on
> the lock that the prepared xact is holding. From a database management
> standpoint that is unacceptable --- it means for instance that you can't
> shut down the database cleanly while such a prepared transaction is
> pending. The difference from a regular table is that no such automatic
> action is taken at backend exit for regular tables.
>
> The whole business of having restrictions on temp table access is
> annoying; I wish we could get rid of them not add complexity to
> enforcing them. The local-buffer-management end of the issue seems
> readily solvable: we need only decree that PREPARE has to flush out any
> dirty local buffers (and maybe discard local buffers altogether, not
> sure). But I've not been able to see a decent solution to the lock
> behavior.
>
> regards, tom lane
>
>