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

   1 =head1 NAME
   2
   3 memcached_get, memcached_mget, memcached_fetch - Get a value
   4
   5 =head1 LIBRARY
   6
   7 C Client Library for memcached (libmemcached, -lmemcached)
   8
   9 =head1 SYNOPSIS
  10
  11   #include <memcached.h>
  12
  13   memcached_result_st *
  14   memcached_fetch_result(memcached_st *ptr,
  15                        memcached_result_st *result,
  16                        memcached_return *error);
  17
  18   char *memcached_get (memcached_st *ptr,
  19                        const char *key, size_t key_length,
  20                        size_t *value_length,
  21                        uint32_t *flags,
  22                        memcached_return *error);
  23
  24   memcached_return
  25   memcached_mget (memcached_st *ptr,
  26                   const char * const *keys,
  27                   const size_t *key_length,
  28                   size_t number_of_keys);
  29   char *
  30   memcached_get_by_key(memcached_st *ptr,
  31                        const char *master_key, size_t master_key_length,
  32                        const char *key, size_t key_length,
  33                        size_t *value_length,
  34                        uint32_t *flags,
  35                        memcached_return *error);
  36
  37   memcached_return
  38   memcached_mget_by_key(memcached_st *ptr,
  39                         const char *master_key, size_t master_key_length,
  40                         const char * const *keys,
  41                         const size_t *key_length,
  42                         size_t number_of_keys);
  43
  44   char *memcached_fetch (memcached_st *ptr,
  45                          char *key, size_t *key_length,
  46                          size_t *value_length,
  47                          uint32_t *flags,
  48                          memcached_return *error);
  49
  50   memcached_return
  51   memcached_fetch_execute(memcached_st *ptr,
  52                           memcached_return (*callback[])(memcached_st *ptr, memcached_result_st *result, void *context),
  53                           void *context,
  54                           unsigned int number_of_callbacks);
  55
  56
  57   memcached_return
  58   memcached_mget_execute(memcached_st *ptr,
  59                          const char *master_key,
  60                          size_t master_key_length,
  61                          const char * const *keys,
  62                          const size_t *key_length,
  63                          size_t number_of_keys,
  64                          memcached_execute_function *callback,
  65                          void *context,
  66                          unsigned int number_of_callbacks);
  67
  68
  69 =head1 DESCRIPTION
  70
  71 memcached_get() is used to fetch an individual value from the server. You
  72 must pass in a key and its length to fetch the object. You must supply
  73 three pointer variables which will give you the state of the returned
  74 object.  A uint32_t pointer to contain whatever flags you stored with the value,
  75 a size_t pointer which will be filled with size of of the object, and a
  76 memcached_return pointer to hold any error. The object will be returned
  77 upon success and NULL will be returned on failure. Any object returned by
  78 memcached_get() must be released by the caller application.
  79
  80 memcached_mget() is used to select multiple keys at once. For multiple key
  81 operations it is always faster to use this function. This function always
  82 works asynchronously. memcached_fetch() is then used to retrieve any keys
  83 found. No error is given on keys that are not found. You must call either
  84 memcached_fetch() or memcached_fetch_result() after a successful call to
  85 memcached_mget(). You should continue to call these functions until they
  86 return NULL (aka no more values). If you need to quit in the middle of a
  87 memcached_get() call, execute a memcached_quit(). After you do this, you can
  88 issue new queries against the server.
  89
  90 memcached_fetch() is used to fetch an individual value from the server.
  91 memcached_mget() must always be called before using this method.  You
  92 must pass in a key and its length to fetch the object. You must supply
  93 three pointer variables which will give you the state of the returned
  94 object.  A uint32_t pointer to contain whatever flags you stored with the value,
  95 a size_t pointer which will be filled with size of of the object, and a
  96 memcached_return pointer to hold any error. The object will be returned
  97 upon success and NULL will be returned on failure. MEMCACHD_END is returned
  98 by the *error value when all objects that have been found are returned.
  99 The final value upon MEMCACHED_END is null. Values returned by
 100 memcached_fetch() musted be free'ed by the caller.
 101
 102 memcached_fetch_result() is used to return a memcached_result_st(3) structure
 103 from a memcached server. The result object is forward compatible with changes
 104 to the server. For more information please refer to the memcached_result_st(3)
 105 help. This function will dynamically allocate a result structure for you
 106 if you do not pass one to the function.
 107
 108 memcached_fetch_execute() is a callback function for result sets. Instead
 109 of returning the results to you for processing, it passes each of the
 110 result sets to the list of functions you provide. It passes to the function
 111 a memcached_st that can be cloned for use in the called function (it can not
 112 be used directly). It also passes a result set which does not need to be freed.
 113 Finally it passes a "context". This is just a pointer to a memory reference
 114 you supply the calling function. Currently only one value is being passed
 115 to each function call. In the future there will be an option to allow this
 116 to be an array.
 117
 118 memcached_mget_execute() is similar to memcached_mget(), but it may trigger
 119 the supplied callbacks with result sets while sending out the queries. If
 120 you try to perform a really large multiget with memcached_mget() you may
 121 encounter a deadlock in the OS kernel (we fail to write data to the socket
 122 because the input buffer is full). memcached_mget_execute() solves this
 123 problem by processing some of the results before continuing sending out
 124 requests. Please note that this function is only available in the binary
 125 protocol.
 126
 127 memcached_get_by_key() and memcached_mget_by_key() behave in a similar nature
 128 as memcached_get() and memcached_mget(). The difference is that they take
 129 a master key that is used for determining which server an object was stored
 130 if key partitioning was used for storage.
 131
 132 All of the above functions are not supported when the C<MEMCACHED_BEHAVIOR_USE_UDP>
 133 has been set. Executing any of these functions with this behavior on will result in
 134 C<MEMCACHED_NOT_SUPPORTED> being returned or, for those functions which do not return
 135 a C<memcached_return>, the error function parameter will be set to
 136 C<MEMCACHED_NOT_SUPPORTED>.
 137
 138 =head1 RETURN
 139
 140 All objects returned must be freed by the calling application.
 141 memcached_get() and memcached_fetch() will return NULL on error. You must
 142 look at the value of error to determine what the actual error was.
 143
 144 =head1 HOME
 145
 146 To find out more information please check:
 147 L<http://tangent.org/552/libmemcached.html>
 148
 149 =head1 AUTHOR
 150
 151 Brian Aker, E<lt>brian@tangent.orgE<gt>
 152
 153 =head1 SEE ALSO
 154
 155 memcached(1) libmemcached(3) memcached_strerror(3)
 156
 157 =cut
 158