git.m6w6.name Git - m6w6/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.
 113
 114 memcached_fetch_result() is used to return a memcached_result_st(3) structure
 115 from a memcached server. The result object is forward compatible with changes
 116 to the server. For more information please refer to the memcached_result_st(3)
 117 help. This function will dynamically allocate a result structure for you
 118 if you do not pass one to the function.
 119
 120 memcached_fetch_execute() is a callback function for result sets. Instead
 121 of returning the results to you for processing, it passes each of the
 122 result sets to the list of functions you provide. It passes to the function
 123 a memcached_st that can be cloned for use in the called function (it can not
 124 be used directly). It also passes a result set which does not need to be freed.
 125 Finally it passes a "context". This is just a pointer to a memory reference
 126 you supply the calling function. Currently only one value is being passed
 127 to each function call. In the future there will be an option to allow this
 128 to be an array.
 129
 130 memcached_mget_execute() and memcached_mget_execute_by_key() is
 131 similar to memcached_mget(), but it may trigger the supplied callbacks
 132 with result sets while sending out the queries. If you try to perform
 133 a really large multiget with memcached_mget() you may encounter a
 134 deadlock in the OS kernel (we fail to write data to the socket because
 135 the input buffer is full). memcached_mget_execute() solves this
 136 problem by processing some of the results before continuing sending
 137 out requests. Please note that this function is only available in the
 138 binary protocol.
 139
 140 memcached_get_by_key() and memcached_mget_by_key() behave in a similar nature
 141 as memcached_get() and memcached_mget(). The difference is that they take
 142 a master key that is used for determining which server an object was stored
 143 if key partitioning was used for storage.
 144
 145 All of the above functions are not supported when the C<MEMCACHED_BEHAVIOR_USE_UDP>
 146 has been set. Executing any of these functions with this behavior on will result in
 147 C<MEMCACHED_NOT_SUPPORTED> being returned or, for those functions which do not return
 148 a C<memcached_return_t>, the error function parameter will be set to
 149 C<MEMCACHED_NOT_SUPPORTED>.
 150
 151 =head1 RETURN
 152
 153 All objects returned must be freed by the calling application.
 154 memcached_get() and memcached_fetch() will return NULL on error. You must
 155 look at the value of error to determine what the actual error was.
 156
 157 =head1 HOME
 158
 159 To find out more information please check:
 160 L<https://launchpad.net/libmemcached>
 161
 162 =head1 AUTHOR
 163
 164 Brian Aker, E<lt>brian@tangent.orgE<gt>
 165
 166 =head1 SEE ALSO
 167
 168 memcached(1) libmemcached(3) memcached_strerror(3)
 169
 170 =cut
 171