Re: json api WIP patch

On 01/14/2013 11:02 PM, Andrew Dunstan wrote:
>
> On 01/14/2013 12:52 PM, Andrew Dunstan wrote:
>>
>> On 01/14/2013 11:32 AM, Robert Haas wrote:
>>>
>>> So, how much performance does this lose on json_in() on a large
>>> cstring, as compared with master?
>>
>> That's a good question. I'll try to devise a test.
>>
>>>
>>> I can't shake the feeling that this is adding a LOT of unnecessary
>>> data copying. For one thing, instead of copying every single lexeme
>>> (including the single-character ones?) out of the original object, we
>>> could just store a pointer to the offset where the object starts and a
>>> length, instead of copying it.
>>
>> In the pure pares case (json_in, json_reccv) nothing extra should be
>> copied. On checking this after reading the above I found that wasn't
>> quite the case, and some lexemes (scalars and field names, but not
>> punctuation) were being copied when not needed. I have made a fix
>> (see
>> <https://bitbucket.org/adunstan/pgdevel/commits/139043dba7e6b15f1f9f7675732bd9dae1fb6497>)
>> which I will include in the next version I publish.
>>
>> In the case of string lexemes, we are passing back a de-escaped
>> version, so just handing back pointers to the beginning and end in
>> the input string doesn't work.
>
>
> After a couple of iterations, some performance enhancements to the
> json parser and lexer have ended up with a net performance improvement
> over git tip. On our test rig, the json parse test runs at just over
> 13s per 10000 parses on git tip and approx 12.55s per 10000 parses
> with the attached patch.
>
> Truth be told, I think the lexer changes have more than paid for the
> small cost of the switch to an RD parser. But since the result is a
> net performance win PLUS some enhanced functionality, I think we
> should be all good.
>
>

Latest version of this patch, including some documentation, mainly from
Merlin Moncure but tweaked by me.

cheers

andrew