...
I'm not sure why the mmap() solution is so much slower for you. Perhaps on some systems files opened for reading are mmap'd under the covers. I'm sure it's highly platform-dependent. (My results on MacOSX - see below - are somewhat better.)
Let me return to your original problem though, doing regex operations on files. I modified your two scripts slightly:
I'm sure my results are dependent on something other than the coding style I suspect file/disk cache and paging operates here. Note that we now agree on total match length and split count. However, when the windows VM goes into paging mode the mmap thing falls off the world as I would expect for a thrashing system.
eg small memory (relatively) C:\code\reportlab\demos\gadflypaper>\tmp\sscan0.py xxx_100mb.dat fn=xxx_100mb.dat n=1898737 l=90506416 time=3.55
C:\code\reportlab\demos\gadflypaper>\tmp\sscan1.py xxx_100mb.dat fn=xxx_100mb.dat n=1898737 l=90506416 time=8.25
C:\code\reportlab\demos\gadflypaper>\tmp\sscan1.py xxx_100mb.dat fn=xxx_100mb.dat n=1898737 l=90506416 time=9.77
C:\code\reportlab\demos\gadflypaper>\tmp\sscan0.py xxx_100mb.dat fn=xxx_100mb.dat n=1898737 l=90506416 time=5.09
C:\code\reportlab\demos\gadflypaper>\tmp\sscan1.py xxx_100mb.dat fn=xxx_100mb.dat n=1898737 l=90506416 time=6.17
C:\code\reportlab\demos\gadflypaper>\tmp\sscan0.py xxx_100mb.dat fn=xxx_100mb.dat n=1898737 l=90506416 time=4.64
and large memory C:\code\reportlab\demos\gadflypaper>\tmp\sscan0.py xxx_200mb.dat fn=xxx_200mb.dat n=3797470 l=181012689 time=20.16
C:\code\reportlab\demos\gadflypaper>\tmp\sscan1.py xxx_200mb.dat fn=xxx_200mb.dat n=3797470 l=181012689 time=136.42
At the end of this run I had to wait quite a long time for other things to become responsive (ie things were entirely paged out).
as another data point with sscan0/1.py (slight mods of your code) I get this with a 200mb file on freeBSD 4.9
/usr/RL_HOME/users/robin/sstest: $ python sscan0.py xxx_200mb.dat fn=xxx_200mb.dat n=3797470 l=181012689 time=7.37 /usr/RL_HOME/users/robin/sstest: $ python sscan1.py xxx_200mb.dat fn=xxx_200mb.dat n=3797470 l=181012689 time=129.65 /usr/RL_HOME/users/robin/sstest:
ie the freeBSD vm seems to thrash just as nastily as xp :(
####################################################################
Here I've implemented slightly modified versions of the scanners that you put forward.
eg
#sscan0.py thanks to Bengt
import sys, time, re
fn = sys.argv[1]
rxo = re.compile('XXXXX')def frxsplit(path, rxo, chunksize=4096):
buffer = ''
for chunk in iter((lambda f=open(path,'rb'): f.read(chunksize)),''):
buffer += chunk
pieces = rxo.split(buffer)
for piece in pieces[:-1]: yield piece
buffer = pieces[-1]
yield buffer
l=n=0
t0 = time.time()
for mat in frxsplit(fn,rxo):
n += 1
l += len(mat)
t1 = time.time()print "fn=%s n=%d l=%d time=%.2f" % (fn, n, l, (t1-t0))
#sscan1.py thanks to Skip
import sys, time, mmap, os, re
fn = sys.argv[1]
fh=os.open(fn,os.O_BINARY|os.O_RDONLY)
s=mmap.mmap(fh,0,access=mmap.ACCESS_READ)
l=n=0
t0 = time.time()
for mat in re.split("XXXXX", s):
n += 1
l += len(mat)
t1 = time.time()print "fn=%s n=%d l=%d time=%.2f" % (fn, n, l, (t1 -- Robin Becker -- http://mail.python.org/mailman/listinfo/python-list
