git.m6w6.name Git - m6w6/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                   char **keys, size_t *key_length,
  27                   size_t number_of_keys);
  28   char *
  29   memcached_get_by_key(memcached_st *ptr,
  30                        const char *master_key, size_t master_key_length,
  31                        const char *key, size_t key_length,
  32                        size_t *value_length,
  33                        uint32_t *flags,
  34                        memcached_return *error);
  35
  36   memcached_return
  37   memcached_mget_by_key(memcached_st *ptr,
  38                         const char *master_key, size_t master_key_length,
  39                         char **keys, size_t *key_length,
  40                         size_t number_of_keys);
  41
  42   char *memcached_fetch (memcached_st *ptr,
  43                          char *key, size_t *key_length,
  44                          size_t *value_length,
  45                          uint32_t *flags,
  46                          memcached_return *error);
  47
  48   memcached_return
  49   memcached_fetch_execute(memcached_st *ptr,
  50                           memcached_return (*callback[])(memcached_st *ptr, memcached_result_st *result, void *context),
  51                           void *context,
  52                           unsigned int number_of_callbacks);
  53
  54
  55   memcached_return
  56   memcached_mget_execute(memcached_st *ptr,
  57                          const char *master_key,
  58                          size_t master_key_length,
  59                          const char **keys,
  60                          size_t *key_length,
  61                          size_t number_of_keys,
  62                          memcached_execute_function *callback,
  63                          void *context,
  64                          unsigned int number_of_callbacks);
  65
  66
  67 =head1 DESCRIPTION
  68
  69 memcached_get() is used to fetch an individual value from the server. You
  70 must pass in a key and its length to fetch the object. You must supply
  71 three pointer variables which will give you the state of the returned
  72 object.  A uint32_t pointer to contain whatever flags you stored with the value,
  73 a size_t pointer which will be filled with size of of the object, and a
  74 memcached_return pointer to hold any error. The object will be returned
  75 upon success and NULL will be returned on failure. Any object returned by
  76 memcached_get() must be released by the caller application.
  77
  78 memcached_mget() is used to select multiple keys at once. For multiple key
  79 operations it is always faster to use this function. This function always
  80 works asynchronously. memcached_fetch() is then used to retrieve any keys
  81 found. No error is given on keys that are not found. You must call either
  82 memcached_fetch() or memcached_fetch_result() after a successful call to
  83 memcached_mget(). You should continue to call these functions until they
  84 return NULL (aka no more values). If you need to quit in the middle of a
  85 memcached_get() call, execute a memcached_quit(). After you do this, you can
  86 issue new queries against the server.
  87
  88 memcached_fetch() is used to fetch an individual value from the server.
  89 memcached_mget() must always be called before using this method.  You
  90 must pass in a key and its length to fetch the object. You must supply
  91 three pointer variables which will give you the state of the returned
  92 object.  A uint32_t pointer to contain whatever flags you stored with the value,
  93 a size_t pointer which will be filled with size of of the object, and a
  94 memcached_return pointer to hold any error. The object will be returned
  95 upon success and NULL will be returned on failure. MEMCACHD_END is returned
  96 by the *error value when all objects that have been found are returned.
  97 The final value upon MEMCACHED_END is null. Values returned by
  98 memcached_fetch() musted be free'ed by the caller.
  99
 100 memcached_fetch_result() is used to return a memcached_result_st(3) structure
 101 from a memcached server. The result object is forward compatible with changes
 102 to the server. For more information please refer to the memcached_result_st(3)
 103 help. This function will dynamically allocate a result structure for you
 104 if you do not pass one to the function.
 105
 106 memcached_fetch_execute() is a callback function for result sets. Instead
 107 of returning the results to you for processing, it passes each of the
 108 result sets to the list of functions you provide. It passes to the function
 109 a memcached_st that can be cloned for use in the called function (it can not
 110 be used directly). It also passes a result set which does not need to be freed.
 111 Finally it passes a "context". This is just a pointer to a memory reference
 112 you supply the calling function. Currently only one value is being passed
 113 to each function call. In the future there will be an option to allow this
 114 to be an array.
 115
 116 memcached_mget_execute() is similar to memcached_mget(), but it may trigger
 117 the supplied callbacks with result sets while sending out the queries. If
 118 you try to perform a really large multiget with memcached_mget() you may
 119 encounter a deadlock in the OS kernel (we fail to write data to the socket
 120 because the input buffer is full). memcached_mget_execute() solves this
 121 problem by processing some of the results before continuing sending out
 122 requests. Please note that this function is only available in the binary
 123 protocol.
 124
 125 memcached_get_by_key() and memcached_mget_by_key() behave in a similar nature
 126 as memcached_get() and memcached_mget(). The difference is that they take
 127 a master key that is used for determining which server an object was stored
 128 if key partitioning was used for storage.
 129
 130 All of the above functions are not supported when the C<MEMCACHED_BEHAVIOR_USE_UDP>
 131 has been set. Executing any of these functions with this behavior on will result in
 132 C<MEMCACHED_NOT_SUPPORTED> being returned or, for those functions which do not return
 133 a C<memcached_return>, the error function parameter will be set to
 134 C<MEMCACHED_NOT_SUPPORTED>.
 135
 136 =head1 RETURN
 137
 138 All objects returned must be freed by the calling application.
 139 memcached_get() and memcached_fetch() will return NULL on error. You must
 140 look at the value of error to determine what the actual error was.
 141
 142 =head1 HOME
 143
 144 To find out more information please check:
 145 L<http://tangent.org/552/libmemcached.html>
 146
 147 =head1 AUTHOR
 148
 149 Brian Aker, E<lt>brian@tangent.orgE<gt>
 150
 151 =head1 SEE ALSO
 152
 153 memcached(1) libmemcached(3) memcached_strerror(3)
 154
 155 =cut
 156