memcached - high-performance memory object caching system
This manual page documents briefly the
memory object caching daemon.
is a flexible memory object caching daemon designed to alleviate database load
in dynamic web applications by storing objects in memory. It's based on
libevent to scale to any size needed, and is specifically optimized to avoid
swapping and always use non-blocking I/O.
These programs follow the usual GNU command line syntax. A summary of options
is included below.
Unix socket path to listen on (disables network support).
Permissions (in octal format) for Unix socket created with -s option.
Listen on <ip_addr>; default to INADDR_ANY. This is an important option to
consider as there is no other way to secure the installation. Binding to an
internal or firewalled network interface is suggested.
Run memcached as a daemon.
Assume the identity of <username> (only when run as root).
Use <num> MB memory max to use for object storage; the default is 64 megabytes.
Use <num> max simultaneous connections; the default is 1024.
This option seeks to prevent client starvation by setting a limit to the
number of sequential requests the server will process from an individual
client connection. Once a connection has exceeded this value, the server will
attempt to process I/O on other connections before handling any further
request from this connection. The default value for this option is 20.
Lock down all paged memory. This is a somewhat dangerous option with large
caches, so consult the README and memcached homepage for configuration
Listen on TCP port <num>, the default is port 11211.
Listen on UDP port <num>, the default is port 11211, 0 is off.
Disable automatic removal of items from the cache when out of memory.
Additions will not be possible until adequate space is freed up.
Raise the core file size limit to the maximum allowable.
Use <factor> as the multiplier for computing the sizes of memory chunks that
items are stored in. A lower value may result in less wasted memory depending
on the total amount of memory available and the distribution of item sizes.
The default is 1.25.
Allocate a minimum of <size> bytes for the item key, value, and flags. The
default is 48. If you have a lot of small keys and values, you can get a
significant memory efficiency gain with a lower value. If you use a high
chunk growth factor (-f option), on the other hand, you may want to increase
the size to allow a bigger percentage of your items to fit in the most densely
packed (smallest) chunks.
Disable the use of CAS (and reduce the per-item size by 8 bytes).
Show the version of memcached and a summary of options.
Be verbose during the event loop; print out errors and warnings.
Be even more verbose; same as -v but also print client commands and
Be extremely verbose; same of the above and also print internal state transitions.
Print memcached and libevent licenses.
Override the size of each slab page in bytes. In mundane words, it adjusts the
maximum item size that memcached will accept. You can use the suffixes K and
M to specify the size as well, so use 2000000 or 2000K or 2M if you want a
maximum size of 2 MB per object. It is not recommended to raise this limit above
1 MB due just to performance reasons. The default value is 1 MB.
Print pidfile to <filename>, only used under -d option.
Number of threads to use to process incoming requests. It is
typically not useful to set this higher than the number of CPU cores on the
memcached server. Setting a high number (64 or more) of worker
threads is not recommended. The default is 4.
Use <char> as the delimiter between key prefixes and IDs. This is used for
per-prefix stats reporting. The default is ":" (colon). If this option is
specified, stats collection is turned on automatically; if not, then it may
be turned on by sending the "stats detail on" command to the server.
Try to use large memory pages (if available). Increasing the memory page size
could reduce the number of TLB misses and improve the performance. In order to
get large pages from the OS, memcached will allocate the total item-cache in
one large chunk. Only available if supported on your OS.
Specify the binding protocol to use. By default, the server will
autonegotiate client connections. By using this option, you can
specify the protocol clients must speak. Possible options are "auto"
(the default, autonegotiation behavior), "ascii" and "binary".
Override the default size of each slab page. Default is 1mb. Default is 1m,
minimum is 1k, max is 128m. Adjusting this value changes the item size limit.
Beware that this also increases the number of slabs (use -v to view), and the
overal memory usage of memcached.
The memcached daemon is copyright Danga Interactive and is distributed under
the BSD license. Note that daemon clients are licensed separately.