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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: 2013-01-14 17:52:11
Message-ID: 50F445CB.90905@dunslane.net (view raw or flat)
Thread:
Lists: pgsql-hackers
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.

>
> This is also remarkably thin on comments.

Fair criticism. I'll work on that.

Thanks for looking at this.

cheers

andrew


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