Re: SKIP LOCKED DATA (work in progress)

2014-05-23 21:24 GMT+02:00 Simon Riggs <simon(at)2ndquadrant(dot)com>:

> On 23 May 2014 10:40, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> > If we're pulling syntax out of the air it'd be nice if we could avoid
> > adding new keywords to the grammar.
>
> Oracle, SQLServer and DB2 have this capability. MySQL does not.
>
> SQLServer implements that using the table hint of READPAST. Since that
> whole syntax area is radically different to what we have, it isn't
> easy to maintain code compatibility.
>
> DB2 z/OS 10 provides SKIP LOCKED DATA clause to allow moving past
> already locked rows. That's fairly recent and I don't believe there
> will be many programs using that. DB2 UDB supports some complex
> functionality using DB2_SKIPINSERTED, DB2_EVALUNCOMMITTED and
> DB2_SKIPDELETED, all of which is complex and mostly exists for
> benchmarks, AFAICS.
>
> Oracle uses both SKIP LOCKED and NOWAIT.
>
> PostgreSQL already chose to follow the Oracle syntax when we
> implemented NOWAIT. So my proposal is that we follow the Oracle syntax
> again and use the words SKIP LOCKED.
>
> I don't see any advantage in inventing new syntax that leaves us
> incompatible with Oracle, nor do I see any need to be compatible with
> both Oracle and DB2 since the latter is much less likely to gain us
> anything in practice.
>

+1

Pavel

>
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