Re: patch: function xmltable

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: Craig Ringer <craig(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: patch: function xmltable
Date: 2017-01-24 20:38:49
Message-ID: 20170124203849.2r2xzkraix6qy3i7@alvherre.pgsql
Views: Raw Message | Whole Thread | Download mbox | Resend email
Lists: pgsql-hackers

Pavel Stehule wrote:

> * SELECT (xmltable(..)).* + regress tests
> * compilation and regress tests without --with-libxml

Thanks. I just realized that this is doing more work than necessary --
I think it would be simpler to have tableexpr fill a tuplestore with the
results, instead of just expecting function execution to apply
ExecEvalExpr over and over to obtain the results. So evaluating a
tableexpr returns just the tuplestore, which function evaluation can
return as-is. That code doesn't use the value-per-call interface

I also realized that the expr context callback is not called if there's
an error, which leaves us without shutting down libxml properly. I
added PG_TRY around the fetchrow calls, but I'm not sure that's correct
either, because there could be an error raised in other parts of the
code, after we've already emitted a few rows (for example out of
memory). I think the right way is to have PG_TRY around the execution
of the whole thing rather than just row at a time; and the tuplestore
mechanism helps us with that.

I think it would be good to have a more complex test case in regress --
let's say there is a table with some simple XML values, then we use
XMLFOREST (or maybe one of the table_to_xml functions) to generate a
large document, and then XMLTABLE uses that document as input document.

Please fix.

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

Attachment Content-Type Size
xmltable-36.patch text/plain 171.1 KB

In response to


Browse pgsql-hackers by date

  From Date Subject
Next Message Robert Haas 2017-01-24 20:55:25 Re: Declarative partitioning - another take
Previous Message Pavel Stehule 2017-01-24 20:33:56 Re: PoC plpgsql - possibility to force custom or generic plan