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

   1 .. highlight:: perl
   2
   3
   4 ****
   5 NAME
   6 ****
   7
   8
   9 memcached_get, memcached_mget, memcached_fetch, memcached_mget_execute,
  10 memcached_mget_execute_by_key - Get a value
  11
  12
  13 *******
  14 LIBRARY
  15 *******
  16
  17
  18 C Client Library for memcached (libmemcached, -lmemcached)
  19
  20
  21 ********
  22 SYNOPSIS
  23 ********
  24
  25
  26
  27 .. code-block:: perl
  28
  29    #include <memcached.h>
  30
  31    memcached_result_st *
  32      memcached_fetch_result (memcached_st *ptr,
  33                              memcached_result_st *result,
  34                              memcached_return_t *error);
  35
  36    char *
  37      memcached_get (memcached_st *ptr,
  38                     const char *key, size_t key_length,
  39                     size_t *value_length,
  40                     uint32_t *flags,
  41                     memcached_return_t *error);
  42
  43    memcached_return_t
  44      memcached_mget (memcached_st *ptr,
  45                    const char * const *keys,
  46                    const size_t *key_length,
  47                    size_t number_of_keys);
  48    char *
  49      memcached_get_by_key (memcached_st *ptr,
  50                            const char *master_key, size_t master_key_length,
  51                            const char *key, size_t key_length,
  52                            size_t *value_length,
  53                            uint32_t *flags,
  54                            memcached_return_t *error);
  55
  56    memcached_return_t
  57      memcached_mget_by_key (memcached_st *ptr,
  58                             const char *master_key, size_t master_key_length,
  59                             const char * const *keys,
  60                             const size_t *key_length,
  61                             size_t number_of_keys);
  62
  63    char *
  64      memcached_fetch (memcached_st *ptr,
  65                       char *key, size_t *key_length,
  66                       size_t *value_length,
  67                       uint32_t *flags,
  68                       memcached_return_t *error);
  69
  70    memcached_return_t
  71      memcached_fetch_execute (memcached_st *ptr,
  72                               memcached_execute_fn *callback,
  73                               void *context,
  74                               uint32_t number_of_callbacks);
  75
  76
  77    memcached_return_t
  78      memcached_mget_execute (memcached_st *ptr,
  79                              const char * const *keys,
  80                              const size_t *key_length,
  81                              size_t number_of_keys,
  82                              memcached_execute_fn *callback,
  83                              void *context,
  84                              uint32_t number_of_callbacks);
  85
  86    memcached_return_t
  87      memcached_mget_execute_by_key (memcached_st *ptr,
  88                                     const char *master_key,
  89                                     size_t master_key_length,
  90                                     const char * const *keys,
  91                                     const size_t *key_length,
  92                                     size_t number_of_keys,
  93                                     memcached_execute_fn *callback,
  94                                     void *context,
  95                                     uint32_t number_of_callbacks);
  96
  97
  98
  99 ***********
 100 DESCRIPTION
 101 ***********
 102
 103
 104 memcached_get() is used to fetch an individual value from the server. You
 105 must pass in a key and its length to fetch the object. You must supply
 106 three pointer variables which will give you the state of the returned
 107 object.  A uint32_t pointer to contain whatever flags you stored with the value,
 108 a size_t pointer which will be filled with size of of the object, and a
 109 memcached_return_t pointer to hold any error. The object will be returned
 110 upon success and NULL will be returned on failure. Any object returned by
 111 memcached_get() must be released by the caller application.
 112
 113 memcached_mget() is used to select multiple keys at once. For multiple key
 114 operations it is always faster to use this function. This function always
 115 works asynchronously. memcached_fetch() is then used to retrieve any keys
 116 found. No error is given on keys that are not found. You must call either
 117 memcached_fetch() or memcached_fetch_result() after a successful call to
 118 memcached_mget(). You should continue to call these functions until they
 119 return NULL (aka no more values). If you need to quit in the middle of a
 120 memcached_get() call, execute a memcached_quit(). After you do this, you can
 121 issue new queries against the server.
 122
 123 memcached_fetch() is used to fetch an individual value from the server.
 124 memcached_mget() must always be called before using this method.  You
 125 must pass in a key and its length to fetch the object. You must supply
 126 three pointer variables which will give you the state of the returned
 127 object.  A uint32_t pointer to contain whatever flags you stored with the value,
 128 a size_t pointer which will be filled with size of of the object, and a
 129 memcached_return_t pointer to hold any error. The object will be returned
 130 upon success and NULL will be returned on failure. MEMCACHD_END is returned
 131 by the \*error value when all objects that have been found are returned.
 132 The final value upon MEMCACHED_END is null. Values returned by
 133 memcached_fetch() musted be free'ed by the caller. memcached_fetch() will
 134 be DEPRECATED in the near future, memcached_fetch_result() should be used
 135 instead.
 136
 137 memcached_fetch_result() is used to return a memcached_result_st(3) structure
 138 from a memcached server. The result object is forward compatible with changes
 139 to the server. For more information please refer to the memcached_result_st(3)
 140 help. This function will dynamically allocate a result structure for you
 141 if you do not pass one to the function.
 142
 143 memcached_fetch_execute() is a callback function for result sets. Instead
 144 of returning the results to you for processing, it passes each of the
 145 result sets to the list of functions you provide. It passes to the function
 146 a memcached_st that can be cloned for use in the called function (it can not
 147 be used directly). It also passes a result set which does not need to be freed.
 148 Finally it passes a "context". This is just a pointer to a memory reference
 149 you supply the calling function. Currently only one value is being passed
 150 to each function call. In the future there will be an option to allow this
 151 to be an array.
 152
 153 memcached_mget_execute() and memcached_mget_execute_by_key() is
 154 similar to memcached_mget(), but it may trigger the supplied callbacks
 155 with result sets while sending out the queries. If you try to perform
 156 a really large multiget with memcached_mget() you may encounter a
 157 deadlock in the OS kernel (we fail to write data to the socket because
 158 the input buffer is full). memcached_mget_execute() solves this
 159 problem by processing some of the results before continuing sending
 160 out requests. Please note that this function is only available in the
 161 binary protocol.
 162
 163 memcached_get_by_key() and memcached_mget_by_key() behave in a similar nature
 164 as memcached_get() and memcached_mget(). The difference is that they take
 165 a master key that is used for determining which server an object was stored
 166 if key partitioning was used for storage.
 167
 168 All of the above functions are not supported when the \ ``MEMCACHED_BEHAVIOR_USE_UDP``\
 169 has been set. Executing any of these functions with this behavior on will result in
 170 \ ``MEMCACHED_NOT_SUPPORTED``\  being returned or, for those functions which do not return
 171 a \ ``memcached_return_t``\ , the error function parameter will be set to
 172 \ ``MEMCACHED_NOT_SUPPORTED``\ .
 173
 174
 175 ******
 176 RETURN
 177 ******
 178
 179
 180 All objects returned must be freed by the calling application.
 181 memcached_get() and memcached_fetch() will return NULL on error. You must
 182 look at the value of error to determine what the actual error was.
 183
 184 MEMCACHED_KEY_TOO_BIG is set to error whenever memcached_fetch() was used
 185 and the key was set larger then MEMCACHED_MAX_KEY, which was the largest
 186 key allowed for the original memcached ascii server.
 187
 188
 189 ****
 190 HOME
 191 ****
 192
 193
 194 To find out more information please check:
 195 `https://launchpad.net/libmemcached <https://launchpad.net/libmemcached>`_
 196
 197
 198 ******
 199 AUTHOR
 200 ******
 201
 202
 203 Brian Aker, <brian@tangent.org>
 204
 205
 206 ********
 207 SEE ALSO
 208 ********
 209
 210
 211 memcached(1) libmemcached(3) memcached_strerror(3)
 212