James Mansion wrote:
> Mark Mielke wrote:
>> I recall there being a measurable performance difference between the
>> most liberal parser, and the most optimized parser, back when I wrote
>> one for PostgreSQL. I don't know how good the one in use for
>> PostgreSQL 8.3 is. As to whether the cost is noticeable to people or
>> not - that depends on what they are doing. The problem is that a UUID
>> is pretty big, and parsing it liberally means a loop.
> It just seems odd - I would have thought one would use re2c or ragel
> to generate something and the performance would essentially be O[n] on
> the input length in characters - using either a collection of allowed
> forms or an engine that normalises case and discards the '-'
> characters between any hex pairs.
Instruction level parallelism allows for multiple hex values to be
processed in parallel, whereas a loop relies on branch prediction and
speculative load and store? :-)
The liberal version is difficult to unroll. The strict version is easy
> So yes these would have a control loop. Is that so bad?
> Either way its hard to imagine how parsing a string of this length
> could create a measurable performance issue compared to what will
> happen with the value post parse.
I think so too.
Mark Mielke <mark(at)mielke(dot)cc>
In response to
pgsql-hackers by date
|Next:||From: Tom Dunstan||Date: 2008-02-29 05:40:39|
|Subject: Re: UUID data format 4x-4x-4x-4x-4x-4x-4x-4x|
|Previous:||From: Tom Lane||Date: 2008-02-29 05:05:45|
|Subject: Re: Batch update of indexes on data loading |