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memcached(1)                                                      memcached(1)




NAME

       memcached - high-performance memory object caching system


SYNOPSIS

       memcached [options]


DESCRIPTION

       This  manual page documents briefly the memcached memory object caching
       daemon.

       memcached is a flexible memory object caching daemon designed to  alle-
       viate  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.


OPTIONS

       These programs follow the usual GNU command line syntax. A  summary  of
       options is included below.

       -s <file>
              Unix socket path to listen on (disables network support).

       -a <perms>
              Permissions  (in  octal  format) for Unix socket created with -s
              option.

       -l <ip_addr>
              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.

       -d     Run memcached as a daemon.

       -u <username>
              Assume the identity of <username> (only when run as root).

       -m <num>
              Use  <num>  MB memory max to use for object storage; the default
              is 64 megabytes.

       -c <num>
              Use <num> max simultaneous connections; the default is 1024.

       -R <num>
              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.

       -k     Lock  down all paged memory. This is a somewhat dangerous option
              with large caches, so consult the README and memcached  homepage
              for configuration suggestions.

       -p <num>
              Listen on TCP port <num>, the default is port 11211.

       -U <num>
              Listen on UDP port <num>, the default is port 11211, 0 is off.

       -M     Disable  automatic  removal  of items from the cache when out of
              memory.  Additions will not be possible until adequate space  is
              freed up.

       -r     Raise the core file size limit to the maximum allowable.

       -f <factor>
              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.

       -n <size>
              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.

       -C     Disable  the  use  of  CAS  (and  reduce  the per-item size by 8
              bytes).

       -h     Show the version of memcached and a summary of options.

       -v     Be verbose during the event loop; print out errors and warnings.

       -vv    Be  even more verbose; same as -v but also print client commands
              and responses.

       -i     Print memcached and libevent licenses.

       -P <filename>
              Print pidfile to <filename>, only used under -d option.

       -t <threads>
              Number of threads to use  to  process  incoming  requests.  This
              option  is only meaningful if memcached was compiled with thread
              support enabled. It is typically not useful to set  this  higher
              than  the  number  of  CPU  cores  on  the memcached server. The
              default is 4.

       -D <char>
              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.

       -L     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.

       -B <proto>
              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".

       -I <size>
              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.

       -o <options>
              Comma separated list of extended or experimental options. See -h
              or wiki for up to date list.


LICENSE

       The  memcached daemon is copyright Danga Interactive and is distributed
       under the BSD license. Note that  daemon  clients  are  licensed  sepa-
       rately.


SEE ALSO

       The README file that comes with memcached
       http://www.danga.com/memcached


AUTHOR

       The  memcached daemon was written by Anatoly Vorobey <mellon@pobox.com>
       and Brad Fitzpatrick <brad@danga.com> and the rest of the crew of Danga
       Interactive http://www.danga.com



                                April 11, 2005                    memcached(1)

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