NAME

       memcached_replace - Storing and Replacing Data

SYNOPSIS

       #include <libmemcached/memcached.h>
              Compile and link with -lmemcached

       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)

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_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  tested  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 VALUE

       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 legitimate error in
       the case of a collision.

SEE ALSO

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