git.m6w6.name Git - awesomized/libmemcached/blob - docs/memcached_get.rst

   1 ===============================
   2 Retrieving data from the server
   3 ===============================
   4
   5
   6 Get a value
   7
   8
   9 *******
  10 LIBRARY
  11 *******
  12
  13
  14 C Client Library for memcached (libmemcached, -lmemcached)
  15
  16
  17 --------
  18 SYNOPSIS
  19 --------
  20
  21
  22
  23 .. code-block:: perl
  24
  25    #include <libmemcached/memcached.h>
  26
  27    memcached_result_st *
  28      memcached_fetch_result (memcached_st *ptr,
  29                              memcached_result_st *result,
  30                              memcached_return_t *error);
  31
  32    char *
  33      memcached_get (memcached_st *ptr,
  34                     const char *key, size_t key_length,
  35                     size_t *value_length,
  36                     uint32_t *flags,
  37                     memcached_return_t *error);
  38
  39    memcached_return_t
  40      memcached_mget (memcached_st *ptr,
  41                    const char * const *keys,
  42                    const size_t *key_length,
  43                    size_t number_of_keys);
  44    char *
  45      memcached_get_by_key (memcached_st *ptr,
  46                            const char *master_key, size_t master_key_length,
  47                            const char *key, size_t key_length,
  48                            size_t *value_length,
  49                            uint32_t *flags,
  50                            memcached_return_t *error);
  51
  52    memcached_return_t
  53      memcached_mget_by_key (memcached_st *ptr,
  54                             const char *master_key, size_t master_key_length,
  55                             const char * const *keys,
  56                             const size_t *key_length,
  57                             size_t number_of_keys);
  58
  59    char *
  60      memcached_fetch (memcached_st *ptr,
  61                       char *key, size_t *key_length,
  62                       size_t *value_length,
  63                       uint32_t *flags,
  64                       memcached_return_t *error);
  65
  66    memcached_return_t
  67      memcached_fetch_execute (memcached_st *ptr,
  68                               memcached_execute_fn *callback,
  69                               void *context,
  70                               uint32_t number_of_callbacks);
  71
  72
  73    memcached_return_t
  74      memcached_mget_execute (memcached_st *ptr,
  75                              const char * const *keys,
  76                              const size_t *key_length,
  77                              size_t number_of_keys,
  78                              memcached_execute_fn *callback,
  79                              void *context,
  80                              uint32_t number_of_callbacks);
  81
  82    memcached_return_t
  83      memcached_mget_execute_by_key (memcached_st *ptr,
  84                                     const char *master_key,
  85                                     size_t master_key_length,
  86                                     const char * const *keys,
  87                                     const size_t *key_length,
  88                                     size_t number_of_keys,
  89                                     memcached_execute_fn *callback,
  90                                     void *context,
  91                                     uint32_t number_of_callbacks);
  92
  93
  94
  95 -----------
  96 DESCRIPTION
  97 -----------
  98
  99
 100 memcached_get() is used to fetch an individual value from the server. You
 101 must pass in a key and its length to fetch the object. You must supply
 102 three pointer variables which will give you the state of the returned
 103 object.  A uint32_t pointer to contain whatever flags you stored with the value,
 104 a size_t pointer which will be filled with size of of the object, and a
 105 memcached_return_t pointer to hold any error. The object will be returned
 106 upon success and NULL will be returned on failure. Any object returned by
 107 memcached_get() must be released by the caller application.
 108
 109 memcached_mget() is used to select multiple keys at once. For multiple key
 110 operations it is always faster to use this function. This function always
 111 works asynchronously. memcached_fetch() is then used to retrieve any keys
 112 found. No error is given on keys that are not found. You must call either
 113 memcached_fetch() or memcached_fetch_result() after a successful call to
 114 memcached_mget(). You should continue to call these functions until they
 115 return NULL (aka no more values). If you need to quit in the middle of a
 116 memcached_get() call, execute a memcached_quit(). After you do this, you can
 117 issue new queries against the server.
 118
 119 memcached_fetch() is used to fetch an individual value from the server.
 120 memcached_mget() must always be called before using this method.  You
 121 must pass in a key and its length to fetch the object. You must supply
 122 three pointer variables which will give you the state of the returned
 123 object.  A uint32_t pointer to contain whatever flags you stored with the value,
 124 a size_t pointer which will be filled with size of of the object, and a
 125 memcached_return_t pointer to hold any error. The object will be returned
 126 upon success and NULL will be returned on failure. MEMCACHD_END is returned
 127 by the \*error value when all objects that have been found are returned.
 128 The final value upon MEMCACHED_END is null. Values returned by
 129 memcached_fetch() musted be free'ed by the caller. memcached_fetch() will
 130 be DEPRECATED in the near future, memcached_fetch_result() should be used
 131 instead.
 132
 133 memcached_fetch_result() is used to return a memcached_result_st(3) structure
 134 from a memcached server. The result object is forward compatible with changes
 135 to the server. For more information please refer to the memcached_result_st(3)
 136 help. This function will dynamically allocate a result structure for you
 137 if you do not pass one to the function.
 138
 139 memcached_fetch_execute() is a callback function for result sets. Instead
 140 of returning the results to you for processing, it passes each of the
 141 result sets to the list of functions you provide. It passes to the function
 142 a memcached_st that can be cloned for use in the called function (it can not
 143 be used directly). It also passes a result set which does not need to be freed.
 144 Finally it passes a "context". This is just a pointer to a memory reference
 145 you supply the calling function. Currently only one value is being passed
 146 to each function call. In the future there will be an option to allow this
 147 to be an array.
 148
 149 memcached_mget_execute() and memcached_mget_execute_by_key() is
 150 similar to memcached_mget(), but it may trigger the supplied callbacks
 151 with result sets while sending out the queries. If you try to perform
 152 a really large multiget with memcached_mget() you may encounter a
 153 deadlock in the OS kernel (we fail to write data to the socket because
 154 the input buffer is full). memcached_mget_execute() solves this
 155 problem by processing some of the results before continuing sending
 156 out requests. Please note that this function is only available in the
 157 binary protocol.
 158
 159 memcached_get_by_key() and memcached_mget_by_key() behave in a similar nature
 160 as memcached_get() and memcached_mget(). The difference is that they take
 161 a master key that is used for determining which server an object was stored
 162 if key partitioning was used for storage.
 163
 164 All of the above functions are not testsed when the \ ``MEMCACHED_BEHAVIOR_USE_UDP``\
 165 has been set. Executing any of these functions with this behavior on will result in
 166 \ ``MEMCACHED_NOT_SUPPORTED``\  being returned or, for those functions which do not return
 167 a \ ``memcached_return_t``\ , the error function parameter will be set to
 168 \ ``MEMCACHED_NOT_SUPPORTED``\ .
 169
 170
 171 ******
 172 RETURN
 173 ******
 174
 175
 176 All objects returned must be freed by the calling application.
 177 memcached_get() and memcached_fetch() will return NULL on error. You must
 178 look at the value of error to determine what the actual error was.
 179
 180 MEMCACHED_KEY_TOO_BIG is set to error whenever memcached_fetch() was used
 181 and the key was set larger then MEMCACHED_MAX_KEY, which was the largest
 182 key allowed for the original memcached ascii server.
 183
 184
 185 ****
 186 HOME
 187 ****
 188
 189
 190 To find out more information please check:
 191 `https://launchpad.net/libmemcached <https://launchpad.net/libmemcached>`_
 192
 193
 194 ******
 195 AUTHOR
 196 ******
 197
 198
 199 Brian Aker, <brian@tangent.org>
 200
 201
 202 --------
 203 SEE ALSO
 204 --------
 205
 206 :manpage:`memcached(1)` :manpage:`libmemcached(3)` :manpage:`memcached_strerror(3)`