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 *error);
  18
  19   char *memcached_get (memcached_st *ptr,
  20                        const char *key, size_t key_length,
  21                        size_t *value_length,
  22                        uint32_t *flags,
  23                        memcached_return *error);
  24
  25   memcached_return
  26   memcached_mget (memcached_st *ptr,
  27                   const char * const *keys,
  28                   const size_t *key_length,
  29                   size_t number_of_keys);
  30   char *
  31   memcached_get_by_key(memcached_st *ptr,
  32                        const char *master_key, size_t master_key_length,
  33                        const char *key, size_t key_length,
  34                        size_t *value_length,
  35                        uint32_t *flags,
  36                        memcached_return *error);
  37
  38   memcached_return
  39   memcached_mget_by_key(memcached_st *ptr,
  40                         const char *master_key, size_t master_key_length,
  41                         const char * const *keys,
  42                         const size_t *key_length,
  43                         size_t number_of_keys);
  44
  45   char *memcached_fetch (memcached_st *ptr,
  46                          char *key, size_t *key_length,
  47                          size_t *value_length,
  48                          uint32_t *flags,
  49                          memcached_return *error);
  50
  51   memcached_return
  52   memcached_fetch_execute(memcached_st *ptr,
  53                           memcached_return (*callback[])(memcached_st *ptr, memcached_result_st *result, void *context),
  54                           void *context,
  55                           unsigned int number_of_callbacks);
  56
  57
  58   memcached_return
  59   memcached_mget_execute(memcached_st *ptr,
  60                          const char * const *keys,
  61                          const size_t *key_length,
  62                          size_t number_of_keys,
  63                          memcached_execute_function *callback,
  64                          void *context,
  65                          unsigned int number_of_callbacks);
  66
  67   memcached_return
  68   memcached_mget_execute_by_key(memcached_st *ptr,
  69                                 const char *master_key,
  70                                 size_t master_key_length,
  71                                 const char * const *keys,
  72                                 const size_t *key_length,
  73                                 size_t number_of_keys,
  74                                 memcached_execute_function *callback,
  75                                 void *context,
  76                                 unsigned int number_of_callbacks);
  77
  78
  79 =head1 DESCRIPTION
  80
  81 memcached_get() is used to fetch an individual value from the server. You
  82 must pass in a key and its length to fetch the object. You must supply
  83 three pointer variables which will give you the state of the returned
  84 object.  A uint32_t pointer to contain whatever flags you stored with the value,
  85 a size_t pointer which will be filled with size of of the object, and a
  86 memcached_return pointer to hold any error. The object will be returned
  87 upon success and NULL will be returned on failure. Any object returned by
  88 memcached_get() must be released by the caller application.
  89
  90 memcached_mget() is used to select multiple keys at once. For multiple key
  91 operations it is always faster to use this function. This function always
  92 works asynchronously. memcached_fetch() is then used to retrieve any keys
  93 found. No error is given on keys that are not found. You must call either
  94 memcached_fetch() or memcached_fetch_result() after a successful call to
  95 memcached_mget(). You should continue to call these functions until they
  96 return NULL (aka no more values). If you need to quit in the middle of a
  97 memcached_get() call, execute a memcached_quit(). After you do this, you can
  98 issue new queries against the server.
  99
 100 memcached_fetch() is used to fetch an individual value from the server.
 101 memcached_mget() must always be called before using this method.  You
 102 must pass in a key and its length to fetch the object. You must supply
 103 three pointer variables which will give you the state of the returned
 104 object.  A uint32_t pointer to contain whatever flags you stored with the value,
 105 a size_t pointer which will be filled with size of of the object, and a
 106 memcached_return pointer to hold any error. The object will be returned
 107 upon success and NULL will be returned on failure. MEMCACHD_END is returned
 108 by the *error value when all objects that have been found are returned.
 109 The final value upon MEMCACHED_END is null. Values returned by
 110 memcached_fetch() musted be free'ed by the caller.
 111
 112 memcached_fetch_result() is used to return a memcached_result_st(3) structure
 113 from a memcached server. The result object is forward compatible with changes
 114 to the server. For more information please refer to the memcached_result_st(3)
 115 help. This function will dynamically allocate a result structure for you
 116 if you do not pass one to the function.
 117
 118 memcached_fetch_execute() is a callback function for result sets. Instead
 119 of returning the results to you for processing, it passes each of the
 120 result sets to the list of functions you provide. It passes to the function
 121 a memcached_st that can be cloned for use in the called function (it can not
 122 be used directly). It also passes a result set which does not need to be freed.
 123 Finally it passes a "context". This is just a pointer to a memory reference
 124 you supply the calling function. Currently only one value is being passed
 125 to each function call. In the future there will be an option to allow this
 126 to be an array.
 127
 128 memcached_mget_execute() and memcached_mget_execute_by_key() is
 129 similar to memcached_mget(), but it may trigger the supplied callbacks
 130 with result sets while sending out the queries. If you try to perform
 131 a really large multiget with memcached_mget() you may encounter a
 132 deadlock in the OS kernel (we fail to write data to the socket because
 133 the input buffer is full). memcached_mget_execute() solves this
 134 problem by processing some of the results before continuing sending
 135 out requests. Please note that this function is only available in the
 136 binary protocol.
 137
 138 memcached_get_by_key() and memcached_mget_by_key() behave in a similar nature
 139 as memcached_get() and memcached_mget(). The difference is that they take
 140 a master key that is used for determining which server an object was stored
 141 if key partitioning was used for storage.
 142
 143 All of the above functions are not supported when the C<MEMCACHED_BEHAVIOR_USE_UDP>
 144 has been set. Executing any of these functions with this behavior on will result in
 145 C<MEMCACHED_NOT_SUPPORTED> being returned or, for those functions which do not return
 146 a C<memcached_return>, the error function parameter will be set to
 147 C<MEMCACHED_NOT_SUPPORTED>.
 148
 149 =head1 RETURN
 150
 151 All objects returned must be freed by the calling application.
 152 memcached_get() and memcached_fetch() will return NULL on error. You must
 153 look at the value of error to determine what the actual error was.
 154
 155 =head1 HOME
 156
 157 To find out more information please check:
 158 L<http://tangent.org/552/libmemcached.html>
 159
 160 =head1 AUTHOR
 161
 162 Brian Aker, E<lt>brian@tangent.orgE<gt>
 163
 164 =head1 SEE ALSO
 165
 166 memcached(1) libmemcached(3) memcached_strerror(3)
 167
 168 =cut
 169