git.m6w6.name Git - awesomized/libmemcached/blob - libmemcached/memcached_get.rst

   1 Retrieving data from the server
   2 ===============================
   3
   4 SYNOPSIS
   5 --------
   6
   7 #include <libmemcached/memcached.h>
   8     Compile and link with -lmemcached
   9
  10 .. function:: memcached_result_st * memcached_fetch_result (memcached_st *ptr, memcached_result_st *result, memcached_return_t *error)
  11
  12 .. function:: char * memcached_get (memcached_st *ptr, const char *key, size_t key_length, size_t *value_length, uint32_t *flags, memcached_return_t *error)
  13
  14 .. function:: memcached_return_t memcached_mget (memcached_st *ptr, const char * const *keys, const size_t *key_length, size_t number_of_keys)
  15
  16 .. function:: char * memcached_get_by_key (memcached_st *ptr, const char *group_key, size_t group_key_length, const char *key, size_t key_length, size_t *value_length, uint32_t *flags, memcached_return_t *error)
  17
  18 .. function:: memcached_return_t memcached_mget_by_key (memcached_st *ptr, const char *group_key, size_t group_key_length, const char * const *keys, const size_t *key_length, size_t number_of_keys)
  19
  20 .. function:: memcached_return_t memcached_fetch_execute (memcached_st *ptr, memcached_execute_fn *callback, void *context, uint32_t number_of_callbacks)
  21
  22 .. function:: memcached_return_t memcached_mget_execute (memcached_st *ptr, const char * const *keys, const size_t *key_length, size_t number_of_keys, memcached_execute_fn *callback, void *context, uint32_t number_of_callbacks)
  23
  24 .. function:: memcached_return_t memcached_mget_execute_by_key (memcached_st *ptr, const char *group_key, size_t group_key_length, const char * const *keys, const size_t *key_length, size_t number_of_keys, memcached_execute_fn *callback, void *context, uint32_t number_of_callbacks)
  25
  26 .. type:: memcached_return_t (*memcached_execute_fn)(const memcached_st *ptr, memcached_result_st *result, void *context)
  27
  28
  29 DESCRIPTION
  30 -----------
  31
  32 :func:`memcached_get` is used to fetch an individual value from the server.
  33 You must pass in a key and its length to fetch the object. You must supply
  34 three pointer variables which will give you the state of the returned
  35 object.  A :type:`uint32_t` pointer to contain whatever flags you stored
  36 with the value, a :type:`size_t` pointer which will be filled with size of of
  37 the object, and a :type:`memcached_return_t` pointer to hold any error. The
  38 object will be returned upon success and NULL will be returned on failure. Any
  39 object returned by :func:`memcached_get` must be released by the caller
  40 application.
  41
  42 :func:`memcached_mget` is used to select multiple keys at once. For
  43 multiple key operations it is always faster to use this function.
  44 This function always works asynchronously.
  45
  46 To retrieve data after a successful execution of :func:`memcached_mget`, you
  47 will need to call :func:`memcached_fetch_result`.  You should continue to call
  48 this function until it returns a NULL (i.e. no more values). If you need to quit
  49 in the middle of a :func:`memcached_mget` call, you can execute a
  50 :func:`memcached_quit`, those this is not required.
  51
  52 :func:`memcached_fetch_result` is used to fetch an individual value from the
  53 server. :func:`memcached_mget` must always be called before using this method.
  54 You must pass in a key and its length to fetch the object. You must supply
  55 three pointer variables which will give you the state of the returned object.
  56 A :type:`uint32_t` pointer to contain whatever flags you stored with the value,
  57 a :type:`size_t` pointer which will be filled with size of of the object, and a
  58 :type:`memcached_return_t` pointer to hold any error. The object will be
  59 returned upon success and NULL will be returned on failure. `MEMCACHED_END` is
  60 returned by the \*error value when all objects that have been found have been
  61 returned. The final value upon `MEMCACHED_END` is null.
  62
  63 :func:`memcached_fetch_result` is used to return a :type:`memcached_result_st`
  64 structure from a memcached server. The result object is forward compatible
  65 with changes to the server. For more information please refer to the
  66 :type:`memcached_result_st` help. This function will dynamically allocate a
  67 result structure for you if you do not pass one to the function.
  68
  69 :func:`memcached_fetch_execute` is a callback function for result sets.
  70 Instead of returning the results to you for processing, it passes each of the
  71 result sets to the list of functions you provide. It passes to the function
  72 a :type:`memcached_st` that can be cloned for use in the called
  73 function (it can not be used directly). It also passes a result set which does
  74 not need to be freed. Finally it passes a "context". This is just a pointer to
  75 a memory reference you supply the calling function. Currently only one value
  76 is being passed to each function call. In the future there will be an option
  77 to allow this to be an array.
  78
  79 :func:`memcached_mget_execute` and :func:`memcached_mget_execute_by_key`
  80 is similar to :func:`memcached_mget`, but it may trigger the supplied
  81 callbacks with result sets while sending out the queries. If you try to
  82 perform a really large multiget with :func:`memcached_mget` you may
  83 encounter a deadlock in the OS kernel (it will fail to write data to the
  84 socket because the input buffer is full). :func:`memcached_mget_execute`
  85 solves this problem by processing some of the results before continuing
  86 sending out requests. Please note that this function is only available in
  87 the binary protocol.
  88
  89 :func:`memcached_get_by_key` and :func:`memcached_mget_by_key` behave
  90 in a similar nature as :func:`memcached_get` and :func:`memcached_mget`.
  91 The difference is that they take a master key that is used for determining
  92 which server an object was stored if key partitioning was used for storage.
  93
  94 All of the above functions are not tested when the
  95 `MEMCACHED_BEHAVIOR_USE_UDP` has been set. Executing any of these
  96 functions with this behavior on will result in `MEMCACHED_NOT_SUPPORTED` being
  97 returned, or for those functions which do not return a
  98 :type:`memcached_return_t`, the error function parameter will be set to
  99 `MEMCACHED_NOT_SUPPORTED`.
 100
 101 RETURN VALUE
 102 ------------
 103
 104 All objects retrieved via :func:`memcached_get` or :func:`memcached_get_by_key`
 105 must be freed with :manpage:`free(3)`.
 106
 107 :func:`memcached_get` will return NULL on error.
 108 You must look at the value of error to determine what the actual error was.
 109
 110 :func:`memcached_fetch_execute` return `MEMCACHED_SUCCESS` if
 111 all keys were successful. `MEMCACHED_NOTFOUND` will be returned if no
 112 keys at all were found.
 113
 114 :func:`memcached_fetch_result` sets error
 115 to `MEMCACHED_END` upon successful conclusion.
 116 `MEMCACHED_NOTFOUND` will be returned if no keys at all were found.
 117
 118 SEE ALSO
 119 --------
 120
 121 .. only:: man
 122
 123     :manpage:`memcached(1)`
 124     :manpage:`libmemcached(3)`
 125     :manpage:`memcached_strerror(3)`
 126
 127 .. only:: html
 128
 129     * :manpage:`memcached(1)`
 130     * :doc:`../libmemcached`
 131     * :doc:`memcached_strerror`