[antlr-interest] Re: Local lookahead depth

Anthony W Youngman Anthony.Youngman at ECA-International.com
Fri Nov 14 07:19:56 PST 2003


I agree with Oliver !!!

Have you EVER hit this sort of problem in real life? I reduced an
estimated run time of about a week, to an actual run time of under an
hour, by eliminating disk access from a program. (The estimate was
achieved by extrapolating from partial runs.)

And as Oliver may remember :-) I was in a spat on the relational theory
newsgroup (which has died down now) about how Pick will smoke SQL for
speed. While performance may be similar while all the data is cached in
RAM, as soon as there is any hint of disk thrashing SQL will be hammered
while Pick is hardly affected - because you can prove mathematically
that Pick disk i/o is almost optimally perfect :-) Would YOU try running
a 32-user interactive db on a 386 with 16Mb ram? We did the equivalent,
and it was plenty fast (actually, it was a MIPS R3000).

Cheers,
Wol

-----Original Message-----
From: Oliver Zeigermann [mailto:oliver at zeigermann.de] 
Sent: 10 November 2003 07:23
To: antlr-interest at yahoogroups.com
Subject: [antlr-interest] Re: Local lookahead depth

> > 
> > I have the same experience. But consider extremely large amounts 
> of 
> > input to be parsed. In this case it is prohibitve to generate an 
> AST 
> > because of the memory issue. As a very practical exmaple I have 
> parsing 
> > of the AMM (Aircraft Maintenance Manual) which is available in 
> SGML 
> > (very hard to parse, really). I parsed this a few years using 
> ANTLR, but 
> > its size normally is around 100MB. A few years ago my machine had 
> 128MB 
> > of RAM! You see what I mean?
> 
> And how much disk space did you have?  On a UNIX box, mmap() is a 
> good way of automating file I/O, but even on systems without virtual 
> memory, you can fake it. Performance is not an issue--with a problem 
> of this size, nothing stays in the processor cache, and the overhead 
> of the disk writes will be only a few percent.
> 
> --Loring


Loring,

are you really serious about this? Have a look at the DOM vs. SAX
discussion in the XML area...

Oliver


 

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