MEMCACHED_SET(3) libmemcached MEMCACHED_SET(3)NAMEmemcached_set - 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 expi‐
ration, 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 expi‐
ration, 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 expi‐
ration, 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 expi‐
ration, 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 expi‐
ration, uint32_t flags)
Compile and link with -lmemcached
DESCRIPTIONmemcached_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 charac‐
ters 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_BEHAV‐
IOR_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_BEHAV‐
IOR_BINARY_PROTOCOL, the size of the key,value, flags and expiry com‐
bined may not exceed 1368 bytes. When running with the ASCII protocol,
the exact limit fluctuates depending on which function is being exe‐
cuted 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 ALSOmemcached(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 09, 2014 MEMCACHED_SET(3)