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ProFTPD module mod_statcache
ProFTPD module mod_statcache
The mod_statcache module is designed to cache the results
of stat(2) and lstat(2) calls in shared memory,
so that the results can be shared among multiple session processes. On
a busy server, especially one handling many directory listings, these
stat(2)/lstat(2) calls can add quite a bit of
overhead.
This module is contained in the mod_statcache.c file for
ProFTPD 1.3.x, and is not compiled by default. Installation
instructions are discussed here. More examples
of mod_statcache usage can be found here.
The most current version of mod_statcache is distributed with the
ProFTPD source code.
Author
Please contact TJ Saunders <tj at castaglia.org> with any
questions, concerns, or suggestions regarding this module.
Directives
Control Actions
Syntax: StatCacheCapacity count
Default: StatCacheCapacity 5000
Context: server config
Module: mod_statcache
Compatibility: 1.3.4rc2 and later
The StatCacheCapacity directive configures the capacity
of the cache, i.e. the maximum number of cache entries. By default,
mod_statcache allocates space for 5000 cache entries.
The count value be 10 or greater. The configured count
is handled as a hint; the actual allocated capacity may be rounded up
to the nearest multiple of the internal block sizes.
Syntax: StatCacheControlsACLs actions|"all" "allow"|"deny" "user"|"group" list
Default: None
Context: server config
Module: mod_statcache
Compatibility: 1.3.4rc2 and later
The StatCacheControlsACLs directive configures access lists of
users or groups who are allowed (or denied) the ability to
use the actions implemented by mod_statcache. The default
behavior is to deny everyone unless an ACL allowing access has been explicitly
configured.
If "allow" is used, then list, a comma-delimited list
of users or groups, can use the given actions; all
others are denied. If "deny" is used, then the list of
users or groups cannot use actions all others are
allowed. Multiple StatCacheControlsACLs directives may be used to
configure ACLs for different control actions, and for both users and groups.
The action provided by mod_statcache is
"statcache".
Examples:
# Allow only user root to examine cache stats
StatCacheControlsACLs all allow user root
Syntax: StatCacheEngine on|off
Default: StatCacheEngine off
Context: server config, <VirtualHost>, <Global>
Module: mod_statcache
Compatibility: 1.3.4rc2 and later
The StatCacheEngine directive enables or disables the module's
caching of stat(2) and lstat(2) calls.
Syntax: StatCacheMaxAge positive-cache-age [negative-cache-age]
Default: StatCacheMaxAge 5
Context: server config
Module: mod_statcache
Compatibility: 1.3.4rc2 and later
The StatCacheMaxAge directive configures how long the
mod_statcache module will keep the stat(2) or
lstat(2) results cached for a given path. By default,
mod_statcache will cache results for 5 seconds (and will
cache failed stat(2)/lstat(2) calls for
1 second).
If you configure a single age parameter, then that value will be used for
both positive and negative cache entries. Thus:
StatCacheMaxAge 300
will cache successful and failed
stat(2)/lstat(2) calls for 5 minutes (300 seconds).
To disable caching of failed stat(2)/lstat(2) calls
entirely, use a negative-cache-age value of zero, e.g.:
# Cache lookups for 60 seconds, and do not cache failed lookups
StatCacheMaxAge 60 0
Syntax: StatCacheTable path
Default: None
Context: server config
Module: mod_statcache
Compatibility: 1.3.4rc2 and later
The StatCacheTable directive configures a path to a file
that mod_statcache uses for handling its cache data. The given
path must be an absolute path. Note: this directive is
required for mod_statcache to function. It is recommended
that this file not be on an NFS mounted partition.
Note that statcache data is not kept across daemon stop/starts. That is,
once proftpd is shutdown, all current statcache data is lost.
Control Actions
Syntax: ftpdctl statcache info|dump
Purpose: Display statcache information
The statcache action is used to display cache statistics about
the statcache data maintained by mod_statcache. For example:
# ftpdctl statcache info
ftpdctl: hits 773, misses 67: 92.0% hit rate
ftpdctl: expires 22, rejects 0
ftpdctl: current count: 1 (of 5000) (0.0% usage)
ftpdctl: highest count: 45 (of 5000) (0.9% usage)
To dump out the entire cache contents (not recommended on a busy server),
you can use:
# ftpdctl statcache dump
The mod_statcache module is distributed with ProFTPD. For
including mod_statcache as a statically linked module, use:
$ ./configure --with-modules=mod_statcache
To build mod_statcache as a DSO module:
$ ./configure --enable-dso --with-shared=mod_statcache
Then follow the usual steps:
$ make
$ make install
For those with an existing ProFTPD installation, you can use the
prxs tool to add mod_statcache, as a DSO module, to
your existing server:
$ prxs -c -i -d mod_statcache.c
Note: Use of the mod_statcache module will
interfere with the mod_vroot and mod_quotatab
modules.
The mod_statcache module works by allocating a SysV shared
memory segment. The different proftpd session processes
then attach to that shared memory segment so that they can share statcache
results.
Example configuration:
<IfModule mod_statcache.c>
StatCacheEngine on
StatCacheTable /var/run/proftpd/statcache.tab
</IfModule>
© Copyright 2013-2017 TJ Saunders
All Rights Reserved
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