On 09/30/2014 02:39 PM, Kevin Grittner wrote:
> Josh Berkus <josh@agliodbs.com> wrote:
>> On 09/30/2014 07:15 AM, Kevin Grittner wrote:
>
>>> At the risk of pushing people away from this POV, I'll point out
>>> that this is somewhat similar to what we do for unlogged bulk loads
>>> -- if all the conditions for doing it the fast way are present, we
>>> do it the fast way; otherwise it still works, but slower.
>>
>> Except that switching between fast/slow bulk loads affects *only* the
>> speed of loading, not the locking rules. Having a statement silently
>> take a full table lock when we were expecting it to be concurrent
>> (because, for example, the index got rebuilt and someone forgot the
>> UNIQUE) violates POLA from my perspective.
>
> I would not think that an approach which took a full table lock to
> implement the more general case would be accepted.
Why not? There are certainly cases ... like bulk loading ... where
users would find it completely acceptable. Imagine that you're merging
3 files into a single unlogged table before processing them into
finished data.
--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com