Re: Huge input lookup exception when trying to create the index for XML data type column in postgreSQL

On Fri, Sep 8, 2023 at 11:39 AM Dominique Devienne <ddevienne(at)gmail(dot)com>
wrote:

> On Thu, Sep 7, 2023 at 10:22 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> Erik Wienhold <ewie(at)ewie(dot)name> writes:
>> > Looks like "Huge input lookup" as reported in [1] (also from Sai) and
>> that
>> > error is from libxml.
>>
>> Ah, thanks for the pointer. It looks like for the DOCUMENT case,
>> we could maybe relax this restriction by passing the XML_PARSE_HUGE
>> option to xmlCtxtReadDoc(). However, there are things to worry about:
>>
>
> Just a remark from the sidelines, from someone having done a fair bit of
> XML in years past.
>
> That XPath is simple, and a streaming parser (SAX or StAX) could handle
> it. While that
> XML_PARSE_HUGE option probably applies to a DOM parser. So is there a
> work-around
> to somehow force using a streaming parser instead of one that must produce
> the whole Document,
> just so a few elements are picked out of it? FWIW. --DD
>

If push comes to shove, the streaming-based extraction can be done outside
the DB, stored in a new column
or table, and index that instead. This is in fact exactly the approach I
took on one server handling XML I wrote.

To be honest, in my case, the XMLs were never large, so I used rapidxml
which is also a DOM parser,
but the same principle applies though, i.e. extract the data from the XML
outside the DB using
SAX (push) / StAX (pull), to avoid having a (too) large document in memory
at any time (client or server side). --DD