1 ==========================
2 Storing and Replacing Data
3 ==========================
14 C Client Library for memcached (libmemcached, -lmemcached)
25 #include <libmemcached/memcached.h>
28 memcached_set (memcached_st *ptr,
29 const char *key, size_t key_length,
30 const char *value, size_t value_length,
35 memcached_add (memcached_st *ptr,
36 const char *key, size_t key_length,
37 const char *value, size_t value_length,
42 memcached_replace (memcached_st *ptr,
43 const char *key, size_t key_length,
44 const char *value, size_t value_length,
49 memcached_prepend(memcached_st *ptr,
50 const char *key, size_t key_length,
51 const char *value, size_t value_length,
56 memcached_append(memcached_st *ptr,
57 const char *key, size_t key_length,
58 const char *value, size_t value_length,
62 memcached_cas(memcached_st *ptr,
63 const char *key, size_t key_length,
64 const char *value, size_t value_length,
70 memcached_set_by_key(memcached_st *ptr,
71 const char *master_key, size_t master_key_length,
72 const char *key, size_t key_length,
73 const char *value, size_t value_length,
78 memcached_add_by_key(memcached_st *ptr,
79 const char *master_key, size_t master_key_length,
80 const char *key, size_t key_length,
81 const char *value, size_t value_length,
86 memcached_replace_by_key(memcached_st *ptr,
87 const char *master_key, size_t master_key_length,
88 const char *key, size_t key_length,
89 const char *value, size_t value_length,
94 memcached_prepend_by_key(memcached_st *ptr,
95 const char *master_key, size_t master_key_length,
96 const char *key, size_t key_length,
97 const char *value, size_t value_length,
102 memcached_append_by_key(memcached_st *ptr,
103 const char *master_key, size_t master_key_length,
104 const char *key, size_t key_length,
105 const char *value, size_t value_length,
110 memcached_cas_by_key(memcached_st *ptr,
111 const char *master_key, size_t master_key_length,
112 const char *key, size_t key_length,
113 const char *value, size_t value_length,
125 memcached_set(), memcached_add(), and memcached_replace() are all used to
126 store information on the server. All methods take a key, and its length to
127 store the object. Keys are currently limited to 250 characters by the
128 memcached(1) server. You must also supply a value and a length. Optionally you
129 may tests an expiration time for the object and a 16 byte value (it is
130 meant to be used as a bitmap).
132 memcached_set() will write an object to the server. If an object already
133 exists it will overwrite what is in the server. If the object does not exist
134 it will be written. If you are using the non-blocking mode this function
135 will always return true unless a network error occurs.
137 memcached_replace() replaces an object on the server. If the object is not
138 found on the server an error occurs.
140 memcached_add() adds an object to the server. If the object is found on the
141 server an error occurs, otherwise the value is stored.
143 memcached_prepend() places a segment of data before the last piece of data
144 stored. Currently expiration and key are not used in the server.
146 memcached_append() places a segment of data at the end of the last piece of
147 data stored. Currently expiration and key are not used in the server.
149 memcached_cas() overwrites data in the server as long as the "cas" value is
150 still the same in the server. You can get the cas value of a result by
151 calling memcached_result_cas() on a memcached_result_st(3) structure. At the point
152 that this note was written cas is still buggy in memached. Turning on tests
153 for it in libmemcached(3) is optional. Please see memcached_set() for
154 information on how to do this.
156 memcached_set_by_key(), memcached_add_by_key(), memcached_replace_by_key(),
157 memcached_prepend_by_key(), memcached_append_by_key_by_key(),
158 memcached_cas_by_key() methods all behave in a similar method as the non key
159 methods. The difference is that they use their master_key parameter to map
160 objects to particular servers.
162 If you are looking for performance, memcached_set() with non-blocking IO is
163 the fastest way to store data on the server.
165 All of the above functions are testsed with the \ ``MEMCACHED_BEHAVIOR_USE_UDP``\
166 behavior enabled. But when using these operations with this behavior on, there
167 are limits to the size of the payload being sent to the server. The reason for
168 these limits is that the Memcahed Server does not allow multi-datagram requests
169 and the current server implementation sets a datagram size to 1400 bytes. Due
170 to protocol overhead, the actual limit of the user supplied data is less than
171 1400 bytes and depends on the protocol in use as well as the operation being
172 executed. When running with the binary protocol, \ `` MEMCACHED_BEHAVIOR_BINARY_PROTOCOL``\ ,
173 the size of the key,value, flags and expiry combined may not exceed 1368 bytes.
174 When running with the ASCII protocol, the exact limit fluctuates depending on
175 which function is being executed and whether the function is a cas operation
176 or not. For non-cas ASCII set operations, there are at least 1335 bytes available
177 to split among the key, key_prefix, and value; for cas ASCII operations there are
178 at least 1318 bytes available to split among the key, key_prefix and value. If the
179 total size of the command, including overhead, exceeds 1400 bytes, a \ ``MEMCACHED_WRITE_FAILURE``\
188 All methods return a value of type \ ``memcached_return_t``\ .
189 On success the value will be \ ``MEMCACHED_SUCCESS``\ .
190 Use memcached_strerror() to translate this value to a printable string.
192 For memcached_replace() and memcached_add(), \ ``MEMCACHED_NOTSTORED``\ is a
193 legitmate error in the case of a collision.
201 To find out more information please check:
202 `https://launchpad.net/libmemcached <https://launchpad.net/libmemcached>`_
210 memcached(1) libmemached(3) memcached_strerror(3)