Horton

Re: Regression with large XML data input

Jim Jones <jim.jones@uni-muenster.de>

View thread View on postgr.es
From: Jim Jones <jim.jones@uni-muenster.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Erik Wienhold <ewie@ewie.name>, Michael Paquier <michael@paquier.xyz>, Robert Treat <rob@xzilla.net>, Postgres hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-07-29T14:01:19Z
Lists: pgsql-hackers 

On 29.07.25 14:11, Tom Lane wrote:
> In the original coding, there was a hazard of the node list getting
> leaked if the caller passed parsed_nodes == NULL.  Or at least I
> thought there was.  It may be that all releases of libxml2 are smart
> enough to free the node list if there's no way to pass it back,
> but I guess we had reason not to trust it.  Possibly there's something
> about that in the discussion that led up to 6082b3d5d, though I see
> I neglected to mention it in the commit message.

I see.. thanks for explaining.
I went through the discussions and the libxml2 issue, and I also think
it is prudent to keep it like that :)

Could you add a short comment to it? Something like this:

/*
 * We use a local variable (node_list) to receive the result
 * from xmlParseBalancedChunkMemory(), even though we might
 * eventually return it via parsed_nodes. This ensures that we
 * retain control of the memory and can safely free it here
 * in case of parse errors or early exits.
 *
 * If parsing fails, we free node_list immediately. If parsing
 * succeeds, we assign it to *parsed_nodes (if provided), which
 * will later be attached to the document tree. Otherwise, if
 * the caller is not interested in the parsed nodes (i.e.,
 * parsed_nodes == NULL), we free them immediately.
 *
 */


Thanks!

Best, Jim

Commits

  1. Remove unnecessary complication around xmlParseBalancedChunkMemory.

  2. Avoid regression in the size of XML input that we will accept.

  3. Use xmlParseInNodeContext not xmlParseBalancedChunkMemory.

  4. Revert "Add support for parsing of large XML data (>= 10MB)"