Re: SSI heap_insert and page-level predicate locks

On Wed, Jun 8, 2011 at 5:36 AM, Dan Ports <drkp(at)csail(dot)mit(dot)edu> wrote:
> On Wed, Jun 08, 2011 at 11:23:48AM +0300, Heikki Linnakangas wrote:
>> AFAICS, the check for page lock is actually unnecessary. A page-level
>> lock on a heap only occurs when tuple-level locks are promoted. It is
>> just a coarser-grain representation of holding locks on all tuples on
>> the page, *that exist already*. It is not a "gap" lock like the index
>> locks are, it doesn't need to conflict with inserting new tuples on the
>> page. In fact, if heap_insert chose to insert the tuple on some other
>> heap page, there would have been no conflict.
>
> Yes, it's certainly unnecessary now, given that we never explicitly
> take heap page locks, just tuple- or relation-level.
>
> The only thing I'd be worried about is that at some future point we
> might add heap page locks -- say, for sequential scans that don't read
> the entire relation -- and expect inserts to be tested against them.
> I'm not sure whether we'd actually do this, but we wanted to keep the
> option open during development.

I don't think this is the right time to be rejiggering this stuff
anyway. Our bug count is -- at least to outward appearances --
remarkably low at the moment, considering how much stuff we jammed
into this release. Let's not hastily change things we might later
regret having changed.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company