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

   1 .. highlight:: perl
   2
   3
   4 memcached_get, memcached_mget, memcached_fetch, memcached_mget_execute, memcached_mget_execute_by_key
   5 *****************************************************************************************************
   6
   7
   8 Get a value
   9
  10
  11 *******
  12 LIBRARY
  13 *******
  14
  15
  16 C Client Library for memcached (libmemcached, -lmemcached)
  17
  18
  19 ********
  20 SYNOPSIS
  21 ********
  22
  23
  24
  25 .. code-block:: perl
  26
  27    #include <libmemcached/memcached.h>
  28
  29    memcached_result_st *
  30      memcached_fetch_result (memcached_st *ptr,
  31                              memcached_result_st *result,
  32                              memcached_return_t *error);
  33
  34    char *
  35      memcached_get (memcached_st *ptr,
  36                     const char *key, size_t key_length,
  37                     size_t *value_length,
  38                     uint32_t *flags,
  39                     memcached_return_t *error);
  40
  41    memcached_return_t
  42      memcached_mget (memcached_st *ptr,
  43                    const char * const *keys,
  44                    const size_t *key_length,
  45                    size_t number_of_keys);
  46    char *
  47      memcached_get_by_key (memcached_st *ptr,
  48                            const char *master_key, size_t master_key_length,
  49                            const char *key, size_t key_length,
  50                            size_t *value_length,
  51                            uint32_t *flags,
  52                            memcached_return_t *error);
  53
  54    memcached_return_t
  55      memcached_mget_by_key (memcached_st *ptr,
  56                             const char *master_key, size_t master_key_length,
  57                             const char * const *keys,
  58                             const size_t *key_length,
  59                             size_t number_of_keys);
  60
  61    char *
  62      memcached_fetch (memcached_st *ptr,
  63                       char *key, size_t *key_length,
  64                       size_t *value_length,
  65                       uint32_t *flags,
  66                       memcached_return_t *error);
  67
  68    memcached_return_t
  69      memcached_fetch_execute (memcached_st *ptr,
  70                               memcached_execute_fn *callback,
  71                               void *context,
  72                               uint32_t number_of_callbacks);
  73
  74
  75    memcached_return_t
  76      memcached_mget_execute (memcached_st *ptr,
  77                              const char * const *keys,
  78                              const size_t *key_length,
  79                              size_t number_of_keys,
  80                              memcached_execute_fn *callback,
  81                              void *context,
  82                              uint32_t number_of_callbacks);
  83
  84    memcached_return_t
  85      memcached_mget_execute_by_key (memcached_st *ptr,
  86                                     const char *master_key,
  87                                     size_t master_key_length,
  88                                     const char * const *keys,
  89                                     const size_t *key_length,
  90                                     size_t number_of_keys,
  91                                     memcached_execute_fn *callback,
  92                                     void *context,
  93                                     uint32_t number_of_callbacks);
  94
  95
  96
  97 ***********
  98 DESCRIPTION
  99 ***********
 100
 101
 102 memcached_get() is used to fetch an individual value from the server. You
 103 must pass in a key and its length to fetch the object. You must supply
 104 three pointer variables which will give you the state of the returned
 105 object.  A uint32_t pointer to contain whatever flags you stored with the value,
 106 a size_t pointer which will be filled with size of of the object, and a
 107 memcached_return_t pointer to hold any error. The object will be returned
 108 upon success and NULL will be returned on failure. Any object returned by
 109 memcached_get() must be released by the caller application.
 110
 111 memcached_mget() is used to select multiple keys at once. For multiple key
 112 operations it is always faster to use this function. This function always
 113 works asynchronously. memcached_fetch() is then used to retrieve any keys
 114 found. No error is given on keys that are not found. You must call either
 115 memcached_fetch() or memcached_fetch_result() after a successful call to
 116 memcached_mget(). You should continue to call these functions until they
 117 return NULL (aka no more values). If you need to quit in the middle of a
 118 memcached_get() call, execute a memcached_quit(). After you do this, you can
 119 issue new queries against the server.
 120
 121 memcached_fetch() is used to fetch an individual value from the server.
 122 memcached_mget() must always be called before using this method.  You
 123 must pass in a key and its length to fetch the object. You must supply
 124 three pointer variables which will give you the state of the returned
 125 object.  A uint32_t pointer to contain whatever flags you stored with the value,
 126 a size_t pointer which will be filled with size of of the object, and a
 127 memcached_return_t pointer to hold any error. The object will be returned
 128 upon success and NULL will be returned on failure. MEMCACHD_END is returned
 129 by the \*error value when all objects that have been found are returned.
 130 The final value upon MEMCACHED_END is null. Values returned by
 131 memcached_fetch() musted be free'ed by the caller. memcached_fetch() will
 132 be DEPRECATED in the near future, memcached_fetch_result() should be used
 133 instead.
 134
 135 memcached_fetch_result() is used to return a memcached_result_st(3) structure
 136 from a memcached server. The result object is forward compatible with changes
 137 to the server. For more information please refer to the memcached_result_st(3)
 138 help. This function will dynamically allocate a result structure for you
 139 if you do not pass one to the function.
 140
 141 memcached_fetch_execute() is a callback function for result sets. Instead
 142 of returning the results to you for processing, it passes each of the
 143 result sets to the list of functions you provide. It passes to the function
 144 a memcached_st that can be cloned for use in the called function (it can not
 145 be used directly). It also passes a result set which does not need to be freed.
 146 Finally it passes a "context". This is just a pointer to a memory reference
 147 you supply the calling function. Currently only one value is being passed
 148 to each function call. In the future there will be an option to allow this
 149 to be an array.
 150
 151 memcached_mget_execute() and memcached_mget_execute_by_key() is
 152 similar to memcached_mget(), but it may trigger the supplied callbacks
 153 with result sets while sending out the queries. If you try to perform
 154 a really large multiget with memcached_mget() you may encounter a
 155 deadlock in the OS kernel (we fail to write data to the socket because
 156 the input buffer is full). memcached_mget_execute() solves this
 157 problem by processing some of the results before continuing sending
 158 out requests. Please note that this function is only available in the
 159 binary protocol.
 160
 161 memcached_get_by_key() and memcached_mget_by_key() behave in a similar nature
 162 as memcached_get() and memcached_mget(). The difference is that they take
 163 a master key that is used for determining which server an object was stored
 164 if key partitioning was used for storage.
 165
 166 All of the above functions are not supported when the \ ``MEMCACHED_BEHAVIOR_USE_UDP``\
 167 has been set. Executing any of these functions with this behavior on will result in
 168 \ ``MEMCACHED_NOT_SUPPORTED``\  being returned or, for those functions which do not return
 169 a \ ``memcached_return_t``\ , the error function parameter will be set to
 170 \ ``MEMCACHED_NOT_SUPPORTED``\ .
 171
 172
 173 ******
 174 RETURN
 175 ******
 176
 177
 178 All objects returned must be freed by the calling application.
 179 memcached_get() and memcached_fetch() will return NULL on error. You must
 180 look at the value of error to determine what the actual error was.
 181
 182 MEMCACHED_KEY_TOO_BIG is set to error whenever memcached_fetch() was used
 183 and the key was set larger then MEMCACHED_MAX_KEY, which was the largest
 184 key allowed for the original memcached ascii server.
 185
 186
 187 ****
 188 HOME
 189 ****
 190
 191
 192 To find out more information please check:
 193 `https://launchpad.net/libmemcached <https://launchpad.net/libmemcached>`_
 194
 195
 196 ******
 197 AUTHOR
 198 ******
 199
 200
 201 Brian Aker, <brian@tangent.org>
 202
 203
 204 ********
 205 SEE ALSO
 206 ********
 207
 208
 209 memcached(1) libmemcached(3) memcached_strerror(3)
 210