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 .. c:type:: memcached_return_t (*memcached_execute_fn)(const memcached_st *ptr, memcached_result_st *result, void *context)
  31
  32 Compile and link with -lmemcached
  33
  34
  35 -----------
  36 DESCRIPTION
  37 -----------
  38
  39
  40 :c:func:`memcached_get` is used to fetch an individual value from the server.
  41 You must pass in a key and its length to fetch the object. You must supply
  42 three pointer variables which will give you the state of the returned
  43 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
  44 the object, and a :c:type:`memcached_return_t` pointer to hold any error. The
  45 object will be returned upon success and NULL will be returned on failure. Any
  46 object returned by :c:func:`memcached_get` must be released by the caller
  47 application.
  48
  49 :c:func:`memcached_mget` is used to select multiple keys at once. For
  50 multiple key operations it is always faster to use this function. This function always works asynchronously.
  51
  52 To retrieve data after a successful execution of :c:func:`memcached_mget`, you will need to
  53 call :c:func:`memcached_fetch_result`.  You should continue to call this function until
  54 it returns a NULL (i.e. no more values). If you need to quit in the middle of a
  55 :c:func:`memcached_mget` call, you can execute a :c:func:`memcached_quit`, those this is not required.
  56
  57 :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.
  58 You must pass in a key and its length to fetch the object. You must supply
  59 three pointer variables which will give you the state of the returned
  60 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
  61 object, and a :c:type:`memcached_return_t` pointer to hold any error. The
  62 object will be returned upon success and NULL will be returned on failure. :c:type:`MEMCACHED_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.
  63
  64 :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
  65 with changes to the server. For more information please refer to the
  66 :c: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 :c: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 :c: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 :c:func:`memcached_mget_execute` and :c:func:`memcached_mget_execute_by_key`
  80 is similar to :c: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 :c: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). :c: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 :c:func:`memcached_get_by_key` and :c:func:`memcached_mget_by_key` behave
  90 in a similar nature as :c:func:`memcached_get` and :c: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 :c:type:`MEMCACHED_BEHAVIOR_USE_UDP` has been set. Executing any of these
  96 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`.
  97
  98
  99 ------
 100 RETURN
 101 ------
 102
 103
 104 All objects retrieved via :c:func:`memcached_get` or :c:func:`memcached_get_by_key` must be freed with :manpage:`free(3)`.
 105
 106 :c:func:`memcached_get` will return NULL on
 107 error. You must look at the value of error to determine what the actual error
 108 was.
 109
 110 :c:func:`memcached_fetch_execute` return :c:type:`MEMCACHED_SUCCESS` if
 111 all keys were successful. :c:type:`MEMCACHED_NOTFOUND` will be return if no
 112 keys at all were found.
 113
 114 :c:func:`memcached_fetch_result` sets error
 115 to :c:type:`MEMCACHED_END` upon successful conclusion.
 116 :c:type:`MEMCACHED_NOTFOUND` will be return if no keys at all were found.
 117
 118 ----
 119 HOME
 120 ----
 121
 122
 123 To find out more information please check:
 124 `http://libmemcached.org/ <http://libmemcached.org/>`_
 125
 126
 127 --------
 128 SEE ALSO
 129 --------
 130
 131 :manpage:`memcached(1)` :manpage:`libmemcached(3)` :manpage:`memcached_strerror(3)`