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

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