Re: Don't deform column-by-column in composite_to_json

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: pgsql-hackers(at)postgresql(dot)org, Andrew Dunstan <andrew(at)dunslane(dot)net>
Subject: Re: Don't deform column-by-column in composite_to_json
Date: 2019-02-06 01:53:37
Message-ID: 20190206015337.GA3854@alvherre.pgsql
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On 2019-Feb-01, Andres Freund wrote:

> diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
> index de0d0723b71..8724022df54 100644
> --- a/src/backend/utils/adt/json.c
> +++ b/src/backend/utils/adt/json.c
> @@ -1755,6 +1755,8 @@ composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
> int i;
> bool needsep = false;
> const char *sep;
> + Datum values[MaxHeapAttributeNumber];
> + bool nulls[MaxHeapAttributeNumber];
> sep = use_line_feeds ? ",\n " : ",";

Isn't this putting much more than needed in the stack? Seems like we
could just allocate tupdesc->natts members dynamically. Not sure if we
care: it's about 12 kB; maybe considering palloc overhead, using the
stack is better.

Worth asking. But if this is worth doing here, then it's worth doing in
a lot more places, isn't it?

Álvaro Herrera
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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