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

   1 =head1 NAME
   2
   3 memcached_get, memcached_mget, memcached_fetch, memcached_mget_execute,
   4 memcached_mget_execute_by_key - Get a value
   5
   6 =head1 LIBRARY
   7
   8 C Client Library for memcached (libmemcached, -lmemcached)
   9
  10 =head1 SYNOPSIS
  11
  12   #include <memcached.h>
  13
  14   memcached_result_st *
  15     memcached_fetch_result (memcached_st *ptr,
  16                             memcached_result_st *result,
  17                             memcached_return_t *error);
  18
  19   char *
  20     memcached_get (memcached_st *ptr,
  21                    const char *key, size_t key_length,
  22                    size_t *value_length,
  23                    uint32_t *flags,
  24                    memcached_return_t *error);
  25
  26   memcached_return_t
  27     memcached_mget (memcached_st *ptr,
  28                   const char * const *keys,
  29                   const size_t *key_length,
  30                   size_t number_of_keys);
  31   char *
  32     memcached_get_by_key (memcached_st *ptr,
  33                           const char *master_key, size_t master_key_length,
  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_by_key (memcached_st *ptr,
  41                            const char *master_key, size_t master_key_length,
  42                            const char * const *keys,
  43                            const size_t *key_length,
  44                            size_t number_of_keys);
  45
  46   char *
  47     memcached_fetch (memcached_st *ptr,
  48                      char *key, size_t *key_length,
  49                      size_t *value_length,
  50                      uint32_t *flags,
  51                      memcached_return_t *error);
  52
  53   memcached_return_t
  54     memcached_fetch_execute (memcached_st *ptr,
  55                              memcached_execute_fn *callback,
  56                              void *context,
  57                              uint32_t number_of_callbacks);
  58
  59
  60   memcached_return_t
  61     memcached_mget_execute (memcached_st *ptr,
  62                             const char * const *keys,
  63                             const size_t *key_length,
  64                             size_t number_of_keys,
  65                             memcached_execute_fn *callback,
  66                             void *context,
  67                             uint32_t number_of_callbacks);
  68
  69   memcached_return_t
  70     memcached_mget_execute_by_key (memcached_st *ptr,
  71                                    const char *master_key,
  72                                    size_t master_key_length,
  73                                    const char * const *keys,
  74                                    const size_t *key_length,
  75                                    size_t number_of_keys,
  76                                    memcached_execute_fn *callback,
  77                                    void *context,
  78                                    uint32_t number_of_callbacks);
  79
  80
  81 =head1 DESCRIPTION
  82
  83 memcached_get() is used to fetch an individual value from the server. You
  84 must pass in a key and its length to fetch the object. You must supply
  85 three pointer variables which will give you the state of the returned
  86 object.  A uint32_t pointer to contain whatever flags you stored with the value,
  87 a size_t pointer which will be filled with size of of the object, and a
  88 memcached_return_t pointer to hold any error. The object will be returned
  89 upon success and NULL will be returned on failure. Any object returned by
  90 memcached_get() must be released by the caller application.
  91
  92 memcached_mget() is used to select multiple keys at once. For multiple key
  93 operations it is always faster to use this function. This function always
  94 works asynchronously. memcached_fetch() is then used to retrieve any keys
  95 found. No error is given on keys that are not found. You must call either
  96 memcached_fetch() or memcached_fetch_result() after a successful call to
  97 memcached_mget(). You should continue to call these functions until they
  98 return NULL (aka no more values). If you need to quit in the middle of a
  99 memcached_get() call, execute a memcached_quit(). After you do this, you can
 100 issue new queries against the server.
 101
 102 memcached_fetch() is used to fetch an individual value from the server.
 103 memcached_mget() must always be called before using this method.  You
 104 must pass in a key and its length to fetch the object. You must supply
 105 three pointer variables which will give you the state of the returned
 106 object.  A uint32_t pointer to contain whatever flags you stored with the value,
 107 a size_t pointer which will be filled with size of of the object, and a
 108 memcached_return_t pointer to hold any error. The object will be returned
 109 upon success and NULL will be returned on failure. MEMCACHD_END is returned
 110 by the *error value when all objects that have been found are returned.
 111 The final value upon MEMCACHED_END is null. Values returned by
 112 memcached_fetch() musted be free'ed by the caller. memcached_fetch() will
 113 be DEPRECATED in the near future, memcached_fetch_result() should be used
 114 instead.
 115
 116 memcached_fetch_result() is used to return a memcached_result_st(3) structure
 117 from a memcached server. The result object is forward compatible with changes
 118 to the server. For more information please refer to the memcached_result_st(3)
 119 help. This function will dynamically allocate a result structure for you
 120 if you do not pass one to the function.
 121
 122 memcached_fetch_execute() is a callback function for result sets. Instead
 123 of returning the results to you for processing, it passes each of the
 124 result sets to the list of functions you provide. It passes to the function
 125 a memcached_st that can be cloned for use in the called function (it can not
 126 be used directly). It also passes a result set which does not need to be freed.
 127 Finally it passes a "context". This is just a pointer to a memory reference
 128 you supply the calling function. Currently only one value is being passed
 129 to each function call. In the future there will be an option to allow this
 130 to be an array.
 131
 132 memcached_mget_execute() and memcached_mget_execute_by_key() is
 133 similar to memcached_mget(), but it may trigger the supplied callbacks
 134 with result sets while sending out the queries. If you try to perform
 135 a really large multiget with memcached_mget() you may encounter a
 136 deadlock in the OS kernel (we fail to write data to the socket because
 137 the input buffer is full). memcached_mget_execute() solves this
 138 problem by processing some of the results before continuing sending
 139 out requests. Please note that this function is only available in the
 140 binary protocol.
 141
 142 memcached_get_by_key() and memcached_mget_by_key() behave in a similar nature
 143 as memcached_get() and memcached_mget(). The difference is that they take
 144 a master key that is used for determining which server an object was stored
 145 if key partitioning was used for storage.
 146
 147 All of the above functions are not supported when the C<MEMCACHED_BEHAVIOR_USE_UDP>
 148 has been set. Executing any of these functions with this behavior on will result in
 149 C<MEMCACHED_NOT_SUPPORTED> being returned or, for those functions which do not return
 150 a C<memcached_return_t>, the error function parameter will be set to
 151 C<MEMCACHED_NOT_SUPPORTED>.
 152
 153 =head1 RETURN
 154
 155 All objects returned must be freed by the calling application.
 156 memcached_get() and memcached_fetch() will return NULL on error. You must
 157 look at the value of error to determine what the actual error was.
 158
 159 MEMCACHED_KEY_TOO_BIG is set to error whenever memcached_fetch() was used
 160 and the key was set larger then MEMCACHED_MAX_KEY, which was the largest
 161 key allowed for the original memcached ascii server.
 162
 163 =head1 HOME
 164
 165 To find out more information please check:
 166 L<https://launchpad.net/libmemcached>
 167
 168 =head1 AUTHOR
 169
 170 Brian Aker, E<lt>brian@tangent.orgE<gt>
 171
 172 =head1 SEE ALSO
 173
 174 memcached(1) libmemcached(3) memcached_strerror(3)
 175
 176 =cut
 177