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::  char * memcached_fetch (memcached_st *ptr, char *key, size_t *key_length, size_t *value_length, uint32_t *flags, memcached_return_t *error);
  25
  26 .. c:function::  memcached_return_t memcached_fetch_execute (memcached_st *ptr, memcached_execute_fn *callback, void *context, uint32_t number_of_callbacks);
  27
  28 .. 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);
  29
  30 .. 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);
  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. :c:func:`memcached_fetch()` is then used to
  51 retrieve any keys found. No error is given on keys that are not found. You
  52 must call either :c:func:`memcached_fetch()` or
  53 :c:func:`memcached_fetch_result()` after a successful call to
  54 :c:func:`memcached_mget()`. You should continue to call these functions until
  55 they return NULL (aka no more values). If you need to quit in the middle of a
  56 :c:func:`memcached_get()` call, execute a :c:func:`memcached_quit()`. After you do this, you can issue new queries against the server.
  57
  58 :c:func:`memcached_fetch()` is used to fetch an individual value from the server. :c:func:`memcached_mget()` must always be called before using this method.
  59 You must pass in a key and its length to fetch the object. You must supply
  60 three pointer variables which will give you the state of the returned
  61 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
  62 object, and a :c:type:`memcached_return_t` pointer to hold any error. The
  63 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.
  64 Values returned by :c:func:`memcached_fetch()` must be freed by the caller.
  65 :c:func:`memcached_fetch()` will be DEPRECATED in the near future,
  66 c:func:`memcached_fetch_result()` should be used instead.
  67
  68 :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
  69 with changes to the server. For more information please refer to the
  70 :c:type:`memcached_result_st` help. This function will dynamically allocate a
  71 result structure for you if you do not pass one to the function.
  72
  73 :c:func:`memcached_fetch_execute()` is a callback function for result sets.
  74 Instead of returning the results to you for processing, it passes each of the
  75 result sets to the list of functions you provide. It passes to the function
  76 a :c:type:`memcached_st` that can be cloned for use in the called
  77 function (it can not be used directly). It also passes a result set which does
  78 not need to be freed. Finally it passes a "context". This is just a pointer to
  79 a memory reference you supply the calling function. Currently only one value
  80 is being passed to each function call. In the future there will be an option
  81 to allow this to be an array.
  82
  83 :c:func:`memcached_mget_execute()` and :c:func:`memcached_mget_execute_by_key()`
  84 is similar to :c:func:`memcached_mget()`, but it may trigger the supplied
  85 callbacks with result sets while sending out the queries. If you try to
  86 perform a really large multiget with :c:func:`memcached_mget()` you may
  87 encounter a deadlock in the OS kernel (it will fail to write data to the
  88 socket because the input buffer is full). :c:func:`memcached_mget_execute()`
  89 solves this problem by processing some of the results before continuing
  90 sending out requests. Please note that this function is only available in
  91 the binary protocol.
  92
  93 :c:func:`memcached_get_by_key()` and :c:func:`memcached_mget_by_key()` behave
  94 in a similar nature as :c:func:`memcached_get()` and :c:func:`memcached_mget()`.
  95 The difference is that they take a master key that is used for determining
  96 which server an object was stored if key partitioning was used for storage.
  97
  98 All of the above functions are not tested when the
  99 :c:type:`MEMCACHED_BEHAVIOR_USE_UDP` has been set. Executing any of these
 100 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`.
 101
 102
 103 ------
 104 RETURN
 105 ------
 106
 107
 108 All objects returned must be freed by the calling application.
 109 :c:func:`memcached_get()` and :c:func:`memcached_fetch()` will return NULL on
 110 error. You must look at the value of error to determine what the actual error
 111 was.
 112
 113 :c:func:`memcached_fetch_execute()` return :c:type:`MEMCACHED_SUCCESS` if
 114 all keys were successful. :c:type:`MEMCACHED_NOTFOUND` will be return if no
 115 keys at all were found.
 116
 117 :c:func:`memcached_fetch()` and :c:func:`memcached_fetch_result()` set error
 118 to :c:type:`MEMCACHED_END` upon successful conclusion.
 119 :c:type:`MEMCACHED_NOTFOUND` will be return if no keys at all were found.
 120
 121 :c:type:`MEMCACHED_KEY_TOO_BIG` is set to error whenever :c::func:`memcached_fetch()` was used
 122 and the key was set larger then :c:type:`MEMCACHED_MAX_KEY`, which was the largest
 123 key allowed for the original memcached ascii server.
 124
 125
 126 ----
 127 HOME
 128 ----
 129
 130
 131 To find out more information please check:
 132 `http://libmemcached.org/ <http://libmemcached.org/>`_
 133
 134
 135
 136 --------
 137 SEE ALSO
 138 --------
 139
 140 :manpage:`memcached(1)` :manpage:`libmemcached(3)` :manpage:`memcached_strerror(3)`