4 memcached_set, memcached_add, memcached_replace
5 ***********************************************
16 C Client Library for memcached (libmemcached, -lmemcached)
27 #include <memcached.h>
30 memcached_set (memcached_st *ptr,
31 const char *key, size_t key_length,
32 const char *value, size_t value_length,
37 memcached_add (memcached_st *ptr,
38 const char *key, size_t key_length,
39 const char *value, size_t value_length,
44 memcached_replace (memcached_st *ptr,
45 const char *key, size_t key_length,
46 const char *value, size_t value_length,
51 memcached_prepend(memcached_st *ptr,
52 const char *key, size_t key_length,
53 const char *value, size_t value_length,
58 memcached_append(memcached_st *ptr,
59 const char *key, size_t key_length,
60 const char *value, size_t value_length,
64 memcached_cas(memcached_st *ptr,
65 const char *key, size_t key_length,
66 const char *value, size_t value_length,
72 memcached_set_by_key(memcached_st *ptr,
73 const char *master_key, size_t master_key_length,
74 const char *key, size_t key_length,
75 const char *value, size_t value_length,
80 memcached_add_by_key(memcached_st *ptr,
81 const char *master_key, size_t master_key_length,
82 const char *key, size_t key_length,
83 const char *value, size_t value_length,
88 memcached_replace_by_key(memcached_st *ptr,
89 const char *master_key, size_t master_key_length,
90 const char *key, size_t key_length,
91 const char *value, size_t value_length,
96 memcached_prepend_by_key(memcached_st *ptr,
97 const char *master_key, size_t master_key_length,
98 const char *key, size_t key_length,
99 const char *value, size_t value_length,
104 memcached_append_by_key(memcached_st *ptr,
105 const char *master_key, size_t master_key_length,
106 const char *key, size_t key_length,
107 const char *value, size_t value_length,
112 memcached_cas_by_key(memcached_st *ptr,
113 const char *master_key, size_t master_key_length,
114 const char *key, size_t key_length,
115 const char *value, size_t value_length,
127 memcached_set(), memcached_add(), and memcached_replace() are all used to
128 store information on the server. All methods take a key, and its length to
129 store the object. Keys are currently limited to 250 characters by the
130 memcached(1) server. You must also supply a value and a length. Optionally you
131 may support an expiration time for the object and a 16 byte value (it is
132 meant to be used as a bitmap).
134 memcached_set() will write an object to the server. If an object already
135 exists it will overwrite what is in the server. If the object does not exist
136 it will be written. If you are using the non-blocking mode this function
137 will always return true unless a network error occurs.
139 memcached_replace() replaces an object on the server. If the object is not
140 found on the server an error occurs.
142 memcached_add() adds an object to the server. If the object is found on the
143 server an error occurs, otherwise the value is stored.
145 memcached_prepend() places a segment of data before the last piece of data
146 stored. Currently expiration and key are not used in the server.
148 memcached_append() places a segment of data at the end of the last piece of
149 data stored. Currently expiration and key are not used in the server.
151 memcached_cas() overwrites data in the server as long as the "cas" value is
152 still the same in the server. You can get the cas value of a result by
153 calling memcached_result_cas() on a memcached_result_st(3) structure. At the point
154 that this note was written cas is still buggy in memached. Turning on support
155 for it in libmemcached(3) is optional. Please see memcached_set() for
156 information on how to do this.
158 memcached_set_by_key(), memcached_add_by_key(), memcached_replace_by_key(),
159 memcached_prepend_by_key(), memcached_append_by_key_by_key(),
160 memcached_cas_by_key() methods all behave in a similar method as the non key
161 methods. The difference is that they use their master_key parameter to map
162 objects to particular servers.
164 If you are looking for performance, memcached_set() with non-blocking IO is
165 the fastest way to store data on the server.
167 All of the above functions are supported with the \ ``MEMCACHED_BEHAVIOR_USE_UDP``\
168 behavior enabled. But when using these operations with this behavior on, there
169 are limits to the size of the payload being sent to the server. The reason for
170 these limits is that the Memcahed Server does not allow multi-datagram requests
171 and the current server implementation sets a datagram size to 1400 bytes. Due
172 to protocol overhead, the actual limit of the user supplied data is less than
173 1400 bytes and depends on the protocol in use as well as the operation being
174 executed. When running with the binary protocol, \ `` MEMCACHED_BEHAVIOR_BINARY_PROTOCOL``\ ,
175 the size of the key,value, flags and expiry combined may not exceed 1368 bytes.
176 When running with the ASCII protocol, the exact limit fluctuates depending on
177 which function is being executed and whether the function is a cas operation
178 or not. For non-cas ASCII set operations, there are at least 1335 bytes available
179 to split among the key, key_prefix, and value; for cas ASCII operations there are
180 at least 1318 bytes available to split among the key, key_prefix and value. If the
181 total size of the command, including overhead, exceeds 1400 bytes, a \ ``MEMCACHED_WRITE_FAILURE``\
190 All methods return a value of type \ ``memcached_return_t``\ .
191 On success the value will be \ ``MEMCACHED_SUCCESS``\ .
192 Use memcached_strerror() to translate this value to a printable string.
194 For memcached_replace() and memcached_add(), \ ``MEMCACHED_NOTSTORED``\ is a
195 legitmate error in the case of a collision.
203 To find out more information please check:
204 `https://launchpad.net/libmemcached <https://launchpad.net/libmemcached>`_
212 Brian Aker, <brian@tangent.org>
220 memcached(1) libmemached(3) memcached_strerror(3)