python read file from memory

read_from_mem.py

# We compare/measure reading a file from memory(1) vs reading from filesytem(2)

##################################
### 1. reading file from memory ##
##################################

import time
import mmap

filename = "myfile.txt"

start = time.clock()
txt = open(filename)
# memory-map the file, size 0 means whole file
# mmap.PROT_READ == open for read
mm =  mmap.mmap(txt.fileno(), 0, prot=mmap.PROT_READ)

for i in range(0, 100001):
   #read 10bytes
   mm.read(10)
txt.close()
mm.close()

end = time.clock()

duration= (end - start) * 1000

print "mm_duration::", duration

#results:
"""
(trusty)komu@localhost:~/work$ python read_mmap.py 
mm_duration:: 35.923
(trusty)komu@localhost:~/work$ python read_mmap.py 
mm_duration:: 36.191
(trusty)komu@localhost:~/work$ python read_mmap.py 
mm_duration:: 36.898
"""

######################################
### 2. reading file from filesystem ##
######################################

import time

filename = "myfile.txt"

start = time.clock()
txt = open(filename)

for i in range(0, 100001):
   #read 10bytes
   txt.read(10)
txt.close()

end = time.clock()

duration= (end - start) * 1000

print "duration::", duration


#results:
"""
(trusty)komu@localhost:~/work$ python read.py 
duration:: 110.113
(trusty)komu@localhost:~/work$ python read.py 
duration:: 94.076
(trusty)komu@localhost:~/work$ python read.py 
duration:: 94.838

# Conclusion:
"""
this seems to imply reading from memory is about 3times faster than from filesystem
"""