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Re (tilly) 1: Mega XSLT Batch job - best approach?

by tilly (Archbishop)
on Jan 22, 2002 at 18:23 UTC ( [id://140662]=note: print w/replies, xml ) Need Help??

in reply to Mega XSLT Batch job - best approach?

Given what you would describe I would plan on, one way or another, winding up with LibXSLT inlined in Perl.

But before coding, my next question is how many parallel processes you can profitably run. This is a question of whether you are bound on I/O or CPU. If CPU, then it is generally not worthwhile to run more processes than you have CPUs. If I/O then it depends on your hardware, and what fraction of time is CPU. The last time I tested an I/O bound job, 7 worked best for me. YMMV.

Next try a run of 50-100 pages with LibXSLT, and see if you have a serious memory leak. If memory usage stays flat, then I wouldn't worry about it. If it is clearly leaking but doesn't wind up at a worrying level, note that. If it leaks unacceptably, figure out how many you can do in one "batch".

Now you have cases:

  1. Only worthwhile to run one process, and there is no leak. Then just inline it.
  2. Only worthwhile to run one process, but there is a leak you care about. Then write a script that can take an input file listing 50-100 file names and do those files. In your main script launch batches in system calls. (The idea of the batch is to amortize startup costs.)
  3. Worthwhile to run many processes. Figure out what to run, then run them in parallel, either using Parallel::ForkManager (may well be Linux specific - the NT emulation of fork is not great) or using IPC::Open3 directly as I did at Run commands in parallel.
Two gotchas to think about. How you will handle error handling is one. And the other is that in any sort of, "gather together, set batches off" logic it is very easy to say, "OK, when I have a batch, send it off" but forget that when you finish finding new jobs, you need to run the remainder as a batch.

Good luck, and tell us how it went.

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