Re: beta1 & beta2 & Windows & heavy load

On Sun, Sep 12, 2004 at 08:28:42PM -0400, Tom Lane wrote:

> 1. During CommitSubTransaction, release the lock on the subtransaction's
> XID (but not any of its other locks).  This means that the number of
> locks held due to just transaction XIDs is no more than the subxact
> nesting depth, rather than growing with the number of subcommitted XIDs.
> 
> 2. XactLockTableWait would have to do something like this:
> 
>     for (;;)
>     {
>         wait for lock associated with xid;
>         if (!TransactionIdIsInProgress(xid))
>             break;
>         xid = SubTransGetParent(xid);
>     }

FWIW, this works for me.

> The other question is whether it's worth some extra overhead in
> XactLockTableWait to save on shared memory.  I'm inclined to think it
> is, mainly because you don't get into XactLockTableWait in the first
> place unless you're going to have to block.

Furthermore, the savings are possibly unbounded, so this is a good idea
anyway.  From the example case it's not hard to imagine situations where
we will want lots of subtransactions; just using exceptions in functions
will implicitly open new ones!  (This kind of bothers me because of the
possibly very fast use of Xids, accelerating Xid counter wraparound ...)

-- 
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"La principal característica humana es la tontería"
(Augusto Monterroso)