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Re: patch: function xmltable

From: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
To: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Cc: Craig Ringer <craig(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: patch: function xmltable
Date: 2017-01-18 21:08:07
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers

2017-01-16 23:51 GMT+01:00 Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>:

> Given
> pg5lnfrnm(at)alap3(dot)anarazel(dot)de
> which is going to heavily change how the executor works in this area, I
> am returning this patch to you again.  I would like a few rather minor
> changes:
> 1. to_xmlstr can be replaced with calls to xmlCharStrdup.

I checked this idea, and it doesn't look well - xmlCharStrdup created xml
string in own memory - and it should be explicitly released with xmlFree().
In this case is more practical using PostgreSQL memory context - because
this memory is released safely in exception. I can rename this function to
more conventional pg_xmlCharStrndup. This function can be used more time in
current code.

> 2. don't need xml_xmlnodetostr either -- just use xml_xmlnodetoxmltype
>    (which returns text*) and extract the cstring from the varlena.  It's
>    a bit more wasteful in terms of cycles, but I don't think we care.
>    If we do care, change the function so that it returns cstring, and
>    have the callers that want text wrap it in cstring_to_text.

done - it is related to not too often use case, and possible slowdown is

> 3. have a new perValueCxt memcxt in TableExprState, child of buildercxt,
>    and switch to it just before GetValue() (reset it just before
>    switching).  Then, don't worry about leaks in GetValue.  This way,
>    the text* conversions et al don't matter.


> After that I think we're going to need to get this working on top of
> Andres' changes.  Which I'm afraid is going to be rather major surgery,
> but I haven't looked.

I am waiting on new commits in this area. This moment I have not idea what
will be broken.

attached updated patch with cleaned xml part



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

Attachment: xmltable-31.patch
Description: text/x-patch (161.5 KB)

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