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MEMCACHED_REPLACE(3)             libmemcached             MEMCACHED_REPLACE(3)


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

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

1.0.18                         February 9, 2014           MEMCACHED_REPLACE(3)

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