Re: XactLockTableWait doesn't set wait_event correctly

On 2 December 2016 at 00:28, Robert Haas <robertmhaas@gmail.com> wrote:
> On Wed, Nov 30, 2016 at 6:50 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
>> Obtaining a tuple lock requires two separate actions: First we do
>> LockTuple() and then we do XactLockTableWait().
>
> I think that's kind of a confusing way of looking at it.  LockTuple()
> waits for a "tuple" lmgr lock, and XactLockTableWait waits for a
> "transaction" lmgr lock.  Those two things are both part of a larger
> protocol for managing access to what we refer to as tuple locks at the
> SQL level.  I don't think conflating those things would be a very good
> idea, because it's useful to know which phase you're currently doing -
> e.g. anybody waiting on a tuple lock is not first in the queue.

Why is it useful to know which phase you're at? What can I do with that info?

Why is knowing that you're doing a "transaction lock" more important
than the fact you're doing a tuple lock on a particular db, relation,
page and tuple? The "transaction lock" tells you nothing a user can
act upon to improve the situation.

-- 
Simon Riggs                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services