Re: [Pharo-dev] tricks for XML parsing.

Sent: Thursday, July 14, 2016 at 2:50 AM From: "Jan Vrany" <jan.vrany@fit.cvut.cz> To: pharo-dev@lists.pharo.org Subject: Re: [Pharo-dev] tricks for XML parsing.

On Thu, 2016-07-14 at 01:58 +0200, monty wrote:

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Thanks for the link.

In-place parsing is a non-starter because it means storing the entire input as a string in memory, so you could only parse files that fit in Pharo's address space. The multi-gigabyte OpenStreetMap docs the article mentions would be unparsable with SAX in a 32-bit VM.

I do not understand. I only know expat which does - AFAIK - in-place parsing and surelt does not need the whole input in memory. 

From the article, footnote 3: "This creates a lifetime dependency–the entire source buffer must outlive all document nodes for the technique to work"

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There is always the option of an FFI-based parser, but it shouldn't be a hybrid like Python's minidom (FFI Expat with a Python DOM implementation), because something like that already exists in Smalltalk/X (FFI Expat with a Smalltalk DOM)

I guess you refer to the implementation I did ages ago. 

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and it was slower than a St/X port of XMLParser in my tests (I assume due to the FFI overhead), so it's probably not worth it.

Very, very interesting. Where can I find the benchmarks? 

This was well over a year ago, and it was DOM parsing. I was testing if St/X (your branch, I think) could be supported by XMLParser in addition to Pharo, Squeak, and GS, but I ran into too many incompatibilities, like Monticello not working (had to load in .st files), #new not sending #initialize, not being able to modify the value of a dictionary association directly, #lf/#cr weirdness, so I gave up. But not before hacking it enough to kind-of run and compared it with the other parsers.

I just run a very simple benchmark on 112MB document (http://www.xml-be nchmark.org/downloads.html) and results are quite the opposite: 

Benchmark resut: Generated at :14-07-2016 07:32:25 AM

           Benchmark      Execution Time [ms]      # of M&S GCs [1]      # of newspace GCs [1]   Parameters BenchmarkXML             SAX - VW                    93418                     0                        2060          SAX - XMLSuite                     9921                     0                         410   

As you can see, the latter is roughly 10 times faster. 

That's the VW parser, which is slower than XMLParser. And again, it was of DOM parsing.

I agree my implementation which uses Expat is clearly suboptimal  and need to be improved (for example it does not use a ILC-based  send to driver so you have a lot of cache misses and does a lot  of unnecessary memcpy()s, but this can be easily improved)

Your implementation was fine, and particularly, its XPath/Query was very impressive. I wasn't attacking you. My point was just the hybrid approach built on Expat (which is a non-validating parser, BTW) should be avoided, in case anyone is considering it, based on my experience with minidom vs lxml.etree in Python and with St/X's v2 parser. A parser based on LibXLM2, Xerces, or something else for SAX, DOM, XPath, etc is probably a better way of creating an alternative to pure-Smalltalk parsers.

Jan   

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But a non-hybrid parser with everything (including the DOM) done in C should definitely be faster.

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Sent: Wednesday, July 13, 2016 at 10:27 AM From: stepharo <stepharo@free.fr> To: "Pharo Development List" <pharo-dev@lists.pharo.org> Subject: [Pharo-dev] tricks for XML parsing.

Hi guys

these free books may be interesting for you

     http://aosabook.org/

http://aosabook.org/en/posa/parsing-xml-at-the-speed-of-light.html

stef