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Re: json api WIP patch

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: json api WIP patch
Date: 2013-01-15 16:31:28
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Lists: pgsql-hackers
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 
>> <>) 
>> 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.



Attachment: jsonapi5.patchx
Description: text/plain (127.2 KB)

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