NAME

       memcached_replace - Storing and Replacing Data

SYNOPSIS

       #include <libmemcached/memcached.h>

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

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

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

       memcached_return_t    memcached_set_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)

       memcached_return_t    memcached_add_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)

       memcached_return_t   memcached_replace_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)

       Compile and link with -lmemcached

DESCRIPTION

       memcached_set(),   memcached_add(),   and   memcached_replace()  are  all  used  to  store
       information on the server. All methods take a key, and its length  to  store  the  object.
       Keys  are  currently limited to 250 characters when using either a version of memcached(1)
       which is 1.4 or below, or when using the text protocol. You must supply both a value and a
       length.  Optionally  you store the object. Keys are currently limited to 250 characters by
       the memcached(1) server. You must supply both a value and a  length.  Optionally  you  may
       test  an  expiration  time for the object and a 16 byte value (it is meant to be used as a
       bitmap). "flags" is a 4byte space that is stored alongside of the  main  value.  Many  sub
       libraries make use of this field, so in most cases users should avoid making use of it.

       memcached_set()  will  write  an object to the server. If an object already exists it will
       overwrite what is in the server. If the object does not exist it will be written.  If  you
       are  using  the  non-blocking  mode this function will always return true unless a network
       error occurs.

       memcached_replace() replaces an object on the server. If the object is not  found  on  the
       server an error occurs.

       memcached_add()  adds  an  object  to  the server. If the object is found on the server an
       error occurs, otherwise the value is stored.

       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_set_by_key(), memcached_add_by_key(), and memcached_replace_by_key() methods all
       behave  in  a similar method as the non key methods. The difference is that they use their
       group_key parameter to map objects to particular servers.

       If you are looking for performance, memcached_set() with non-blocking IO  is  the  fastest
       way to store data on the server.

       All  of  the  above  functions  are  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.

       For  memcached_replace()  and memcached_add(), MEMCACHED_NOTSTORED is a legitmate error in
       the case of a collision.

HOME

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

SEE ALSO

       memcached(1) libmemached(3)  memcached_strerror(3)  memcached_prepend(3)  memcached_cas(3)
       memcached_append(3)

AUTHOR

       Brian Aker

COPYRIGHT

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