NAME

       memcached_cas - Working with data on the server in an atomic fashion

SYNOPSIS

       #include <libmemcached/memcached.h>

       memcached_return_t  memcached_cas(memcached_st *ptr,  const  char *key, size_t key_length,
       const char *value, size_t value_length, time_t expiration, uint32_t flags, uint64_t cas)

       memcached_return_t    memcached_cas_by_key(memcached_st *ptr,    const    char *group_key,
       size_t group_key_length,    const   char *key,   size_t key_length,   const   char *value,
       size_t value_length, time_t expiration, uint32_t flags, uint64_t cas)

       Compile and link with -lmemcached

DESCRIPTION

       memcached_cas() overwrites data in the server as long as the "cas" value is still the same
       in  the server. You can get the cas value of a result by calling memcached_result_cas() on
       a memcached_result_st(3) structure. At the point that this note was written cas  is  still
       buggy  in  memached.  Turning  on  tests for it in libmemcached(3) is optional. Please see
       memcached_set() for information on how to do this.

       memcached_cas_by_key() method behaves in a similar method as  the  non  key  methods.  The
       difference is that it uses the group_key parameter to map objects to particular servers.

       memcached_cas()  is testsed with the MEMCACHED_BEHAVIOR_USE_UDP behavior enabled. However,
       when using these operations with this behavior on, there are limits to  the  size  of  the
       payload  being  sent  to  the  server.   The reason for these limits is that the Memcached
       Server does not allow multi-datagram requests and the current server implementation sets a
       datagram  size  to  1400  bytes.  Due  to  protocol overhead, the actual limit of the user
       supplied data is less than 1400 bytes and depends on the protocol in use as, well  as  the
       operation     being     executed.    When    running    with    the    binary    protocol,
       MEMCACHED_BEHAVIOR_BINARY_PROTOCOL, the size of the key,value, flags and  expiry  combined
       may  not  exceed  1368  bytes.  When  running  with  the  ASCII  protocol, the exact limit
       fluctuates depending on which function is being executed and whether the function is a cas
       operation  or  not.  For  non-cas  ASCII  set  operations,  there  are at least 1335 bytes
       available to split among the key, key_prefix, and value; for cas  ASCII  operations  there
       are  at  least  1318  bytes available to split among the key, key_prefix and value. If the
       total   size   of   the   command,   including   overhead,   exceeds   1400    bytes,    a
       MEMCACHED_WRITE_FAILURE will be returned.

RETURN

       All  methods  return  a  value  of  type memcached_return_t.  On success the value will be
       MEMCACHED_SUCCESS.  Use memcached_strerror()  to  translate  this  value  to  a  printable
       string.

HOME

       To find out more information please check: http://libmemcached.org/

SEE ALSO

       memcached(1)  libmemached(3)  memcached_strerror(3)  memcached_set(3)  memcached_append(3)
       memcached_add(3) memcached_prepend(3) memcached_replace(3)

AUTHOR

       Brian Aker

COPYRIGHT

       2011-2013, Brian Aker DataDifferential, http://datadifferential.com/