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Full Discussion: File access:
Top Forums Programming File access: Post 302237925 by jim mcnamara on Thursday 18th of September 2008 04:38:59 PM
Old 09-18-2008
That is exactly why the answer(s) we gave to the original question were somewhat meaningless.

What you are seeing is only the effect of buffer size on the number of times underlying stdio system calls are made. More calls more overhead. Nothing to do necessarily with I/O throughput. Larger buffers do improve performance but there comes a point where doubling buffer size buys almost nothing.

The actual I/O throughput is a function of "hard drive" cache size - our drives are on a giant SAN with RAID support. Buffering is immense. So our "hard drives" are really just a frontend box that pretends it is a disk - fronting for a RAID cluster.

Clearing the cache just means you are measuring disk latency and seek times as well as the other components of I/O.

Last edited by jim mcnamara; 09-18-2008 at 05:44 PM..
 

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IO::Dir(3pm)						 Perl Programmers Reference Guide					      IO::Dir(3pm)

NAME
IO::Dir - supply object methods for directory handles SYNOPSIS
use IO::Dir; $d = IO::Dir->new("."); if (defined $d) { while (defined($_ = $d->read)) { something($_); } $d->rewind; while (defined($_ = $d->read)) { something_else($_); } undef $d; } tie %dir, 'IO::Dir', "."; foreach (keys %dir) { print $_, " " , $dir{$_}->size," "; } DESCRIPTION
The "IO::Dir" package provides two interfaces to perl's directory reading routines. The first interface is an object approach. "IO::Dir" provides an object constructor and methods, which are just wrappers around perl's built in directory reading routines. new ( [ DIRNAME ] ) "new" is the constructor for "IO::Dir" objects. It accepts one optional argument which, if given, "new" will pass to "open" The following methods are wrappers for the directory related functions built into perl (the trailing 'dir' has been removed from the names). See perlfunc for details of these functions. open ( DIRNAME ) read () seek ( POS ) tell () rewind () close () "IO::Dir" also provides an interface to reading directories via a tied hash. The tied hash extends the interface beyond just the directory reading routines by the use of "lstat", from the "File::stat" package, "unlink", "rmdir" and "utime". tie %hash, 'IO::Dir', DIRNAME [, OPTIONS ] The keys of the hash will be the names of the entries in the directory. Reading a value from the hash will be the result of calling "File::stat::lstat". Deleting an element from the hash will delete the corresponding file or subdirectory, provided that "DIR_UNLINK" is included in the "OPTIONS". Assigning to an entry in the hash will cause the time stamps of the file to be modified. If the file does not exist then it will be created. Assigning a single integer to a hash element will cause both the access and modification times to be changed to that value. Alternatively a reference to an array of two values can be passed. The first array element will be used to set the access time and the second element will be used to set the modification time. SEE ALSO
File::stat AUTHOR
Graham Barr. Currently maintained by the Perl Porters. Please report all bugs to <perlbug@perl.org>. COPYRIGHT
Copyright (c) 1997-2003 Graham Barr <gbarr@pobox.com>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.18.2 2013-11-04 IO::Dir(3pm)
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