Top Forums Shell Programming and Scripting Increase the performance of find command. Post 303041939 by jim mcnamara on Saturday 7th of December 2019 09:28:02 AM
This standard library call: nftw (or ftw)
IBM Knowledge Center

supports the find command traversing directory file trees - i.e., searching and locating files.

Assuming you want to keep the command you already have (and I am not sue that Rudi's suggested test is valid because of file and directory caching ):

A limiting factor is known to be the number of sub-directories in the file tree, and possibly the number of available open file descriptors - a per process limit.
If you can parallelize your code using several processes it may improve performance. I'm not sure this will help much because it depends on the number of sub-directories being large to gain any benefit. The developers who write system code try to maximize throughput.

What I'm saying is: performance enhancement work is subjective and often a misplaced resource and a waste of programmer time.
Suppose your command runs in one minute in production. Then you work hard and get it down to 35 seconds. The user perception of "slow" will still be there, so you have to get it down to maybe 6 seconds to make users happy and see it as "faster". In this case getting an order of magnitude improvement may not be possible.

And in this case you would have to do something about directory caching messing up testing because (you check this yourself) once you open a directory the system caches it for speedier access. Use the time command and rerun the command to see what I mean:
time [my long command goes here]
#write down the result
time [my long command goes here]
# write down the result and compare the two resulting times

This User Gave Thanks to jim mcnamara For This Post:
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FTW(3)							   BSD Library Functions Manual 						    FTW(3)

ftw, nftw -- traverse (walk) a file tree SYNOPSIS
#include <ftw.h> int ftw(const char *path, int (*fn)(const char *, const struct stat *ptr, int flag), int depth); int nftw(const char *path, int (*fn)(const char *, const struct stat *ptr, int flag, struct FTW *), int depth, int flags); DESCRIPTION
These functions are provided for compatibility with legacy code. New code should use the fts(3) functions. The ftw() and nftw() functions traverse (walk) the directory hierarchy rooted in path. For each object in the hierarchy, these functions call the function pointed to by fn. The ftw() function passes this function a pointer to a NUL-terminated string containing the name of the object, a pointer to a stat structure corresponding to the object, and an integer flag. The nftw() function passes the aforementioned argu- ments plus a pointer to a FTW structure as defined by <ftw.h> (shown below): struct FTW { int base; /* offset of basename into pathname */ int level; /* directory depth relative to starting point */ }; Possible values for the flag passed to fn are: FTW_F A regular file. FTW_D A directory being visited in pre-order. FTW_DNR A directory which cannot be read. The directory will not be descended into. FTW_DP A directory being visited in post-order (nftw() only). FTW_NS A file for which no stat(2) information was available. The contents of the stat structure are undefined. FTW_SL A symbolic link. FTW_SLN A symbolic link with a non-existent target (nftw() only). The ftw() function traverses the tree in pre-order. That is, it processes the directory before the directory's contents. The depth argument specifies the maximum number of file descriptors to keep open while traversing the tree. It has no effect in this imple- mentation. The nftw() function has an additional flags argument with the following possible values: FTW_PHYS Physical walk, don't follow symbolic links. FTW_MOUNT The walk will not cross a mount point. FTW_DEPTH Process directories in post-order. Contents of a directory are visited before the directory itself. By default, nftw() traverses the tree in pre-order. FTW_CHDIR Change to a directory before reading it. By default, nftw() will change its starting directory. The current working directory will be restored to its original value before nftw() returns. RETURN VALUES
If the tree was traversed successfully, the ftw() and nftw() functions return 0. If the function pointed to by fn returns a non-zero value, ftw() and nftw() will stop processing the tree and return the value from fn. Both functions return -1 if an error is detected. ERRORS
The ftw() and nftw() functions may fail and set errno for any of the errors specified for the library functions close(2), open(2), stat(2), malloc(3), opendir(3) and readdir(3). If the FTW_CHDIR flag is set, the nftw() function may fail and set errno for any of the errors speci- fied for chdir(2). In addition, either function may fail and set errno as follows: [EINVAL] The depth argument is less than 1 or greater than OPEN_MAX. LEGACY ERRORS
The ftw() and nftw() functions are far more tolerant of symlink cycles and are lax in reporting errors while accessing the initial path. When nftw() is passed FTW_MOUNT, it will pass the mount point to the callback function. SEE ALSO
chdir(2), close(2), open(2), stat(2), fts(3), malloc(3), opendir(3), readdir(3), compat(5) STANDARDS
The ftw() and nftw() functions conform to IEEE Std 1003.1-2001 (``POSIX.1'') and Version 3 of the Single UNIX Specification (``SUSv3''). HISTORY
Prior to MacOS X 10.4 ftw did not follow symlinks. BUGS
The depth argument is currently ignored. BSD
May 20, 2003 BSD

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