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[2008-01-16 08:21 UTC] sq6elt at wp dot pl
Description:
------------
With a lot of includes, located deep in file system,
there may be a performance impact, because of a lot of
unnecessary lstats.
Why, when there is exactly specified path, any lstats are made.
Simple access is sufficient, or I missed something?
If some of these are required, then do it only once.
I have checked php4, it behaves in the same way.
There is no difference, when i use include, include_once, require, require_once.
Reproduce code:
---------------
Create a directory tree:
mkdir -p /tmp/a/b/c/d/e/f/g/h/i/j
Two empty php scripts:
echo '<? ?>' > /tmp/a/b/c/d/e/f/g/h/i/j/a.php
echo '<? ?>' > /tmp/a/b/c/d/e/f/g/h/i/j/b.php
and a main script /tmp/t.php
<?
include "/tmp/a/b/c/d/e/f/g/h/i/j/a.php";
include "/tmp/a/b/c/d/e/f/g/h/i/j/b.php";
?>
Actual result:
--------------
Do a strace on t,php
strace /usr/bin/php5 t.php 2>&1 | grep lstat64
And guess what:
lstat64("/usr", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/usr/bin", {st_mode=S_IFDIR|0755, st_size=49152, ...}) = 0
lstat64("/usr/bin/php5", {st_mode=S_IFREG|0755, st_size=5510176, ...}) = 0
lstat64("/etc", {st_mode=S_IFDIR|0755, st_size=8192, ...}) = 0
lstat64("/etc/php5", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/etc/php5/cli", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/etc/php5/cli/php.ini", {st_mode=S_IFREG|0644, st_size=44278, ...}) = 0
lstat64("/tmp", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=8192, ...}) = 0
lstat64("/tmp/t.php", {st_mode=S_IFREG|0644, st_size=94, ...}) = 0
lstat64("/tmp", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=8192, ...}) = 0
lstat64("/tmp/a", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h/i", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h/i/j", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h/i/j/a.php", {st_mode=S_IFREG|0644, st_size=11, ...}) = 0
lstat64("/tmp", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=8192, ...}) = 0
lstat64("/tmp/a", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h/i", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h/i/j", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat64("/tmp/a/b/c/d/e/f/g/h/i/j/b.php", {st_mode=S_IFREG|0644, st_size=7, ...}) = 0
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Last updated: Fri Nov 22 10:01:28 2024 UTC |
From: TSRM/tsrm_virtual_cwd.c if (!realpath(path, resolved_path)) { /* Note: Not threadsafe on older BSD's */ if (use_realpath == CWD_REALPATH) { return 1; } goto no_realpath; } use_realpath = CWD_REALPATH; CWD_STATE_COPY(&old_state, state); Manual page says: BUGS Avoid using this function. It is broken by design... So please avoid use this function, as stated above it has significant performance impact and as stated in manual it's simply broken. For now I have disabled this, by undefining HAVE_REALPATH.From logical point of view, these files are different. Programmers should thread this as different files. Besides, this is broken for hardlinks, only symlinks may be determined by this call. Simple test (rp.c) #include <stdlib.h> #include <string.h> char x[4096]; int main(int argc, char* argv[]) { if (argc != 2 ) { printf("Provide a path %i\n", argc); return 0; } memset(x, 0, 4096); realpath(argv[1], x); printf("Realpath for %s is %s\n", argv[1], x); } $ ./rp /home/ftp/welcome.msg Realpath for /home/ftp/welcome.msg is /home/ftp/welcome.msg $ mkdir /home/t $ mount /home/ftp /home/t --bind $ ./rp /home/t/welcome.msg Realpath for /home/t/welcome.msg is /home/t/welcome.msg So, this is partial solution, and in some environment have big performance impacts. If its really required to know if two files are really the same file, look at stat. $ stat /home/ftp/welcome.msg File: `/home/ftp/welcome.msg' Size: 166 Blocks: 8 IO Block: 4096 regular file Device: 807h/2055d Inode: 67117468 Links: 1 [...] $ stat /home/t/welcome.msg File: `/home/t/welcome.msg' Size: 166 Blocks: 8 IO Block: 4096 regular file Device: 807h/2055d Inode: 67117468 Links: 1 [...] One may determine if two files are really the same by comparing device and inode. This compare do a single stat on target file and not stats on each path element, and solves hard linking.