|Just another Perl shrine|
Re: Minimizing PAR performance hitby tsee (Curate)
|on Jan 08, 2007 at 09:35 UTC||Need Help??|
If I recall correctly --dependent is implied by -P. The reason is somewhat obvious (to me): If you need a Perl interpreter to execute the produced script (for those following along: -P produces a Perl script with all dependencies embedded), it's just pointless to ship a libperl along.
One thing I'd like to point out which I am sure you already know, but some other readers might not, is that the PAR "runtime" performance hit is related to the start-up time only. That is, it takes longer to start, but the performance once its running is identical. False assumptions about this have cropped up in the past.
If you produce a stand-alone .exe using PAR, that .exe will have to do some fancy bootstrapping procedure and ends up creating two processes instead of one. Reason is that it cannot rely on a single (perl) process to do the cleanup up of the temporary data if that was so requested by the packager. After all, the "inner" process is started from the temporary directory itself. I would say this constitutes a good part of the memory overhead.
Validating this, I tried loading the PAR module from a one-liner. This shows an increase of RAM use of about 1.5MB over a one-liner that consists of only "use strict; use warnings;" or about 2MB over one without any "use" statements. This difference between a script that uses PAR and one which doesn't might be further reduced if it uses more of the modules PAR loads internally anyway. Numbers at the end of this post.
The way to go to reduce the memory overhead is certainly to move away from stand-alone executables. Install a perl. Install PAR on the client-side. This is a pure-Perl module since version 0.970 and should install cleanly just about anywhere. Then ship a .par archive to the client. Any script that was packaged indo that .par can be executed with a one-liner:
This should incrementally unpack the necessary files from the .par archive instead of dumping the whole archive's contents to disk. (Don't quote me on this, though.)
Creating a .par archive is reasonably simple: Use the -p (without the -B) option to pp. Since pp (or rather Module::ScanDeps) is a little over-aggressive at including possible dependencies, you might want to unzip the .par into a temporary directory, remove anything that you are sure won't be needed, and then re-zip it. PAR::Dist can help with that a little if this feels uncomfortable.
Of course, unpacking stuff incrementally will be slower over all than dumping it all to disk at start-up. I don't know how much difference this makes, but at least you don't pay the penalty from the separate process, etc.
Finally, I would suggest looking at the PAR FAQ at par.perl.org. It has some good tips for reducing the executable size which might provide some benefit in this case, too.
Hope this helps,
P.S.: The memory numbers as top showed:
There was quite a bit of code added to PAR between 0.92 and 0.970, but 300kb of extra memory kind of surprises me.