1MEMCACHED_GET_BY_KEY(3)      libmemcached-awesome      MEMCACHED_GET_BY_KEY(3)
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NAME

6       memcached_get_by_key - Retrieving data from the server
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SYNOPSIS

9       #include <libmemcached/memcached.h>
10              Compile and link with -lmemcached
11
12       memcached_result_st      *memcached_fetch_result(memcached_st     *ptr,
13       memcached_result_st *result, memcached_return_t *error)
14
15       char  *memcached_get(memcached_st  *ptr,  const   char   *key,   size_t
16       key_length,  size_t  *value_length, uint32_t *flags, memcached_return_t
17       *error)
18
19       memcached_return_t memcached_mget(memcached_st *ptr, const char  *const
20       *keys, const size_t *key_length, size_t number_of_keys)
21
22       char  *memcached_get_by_key(memcached_st  *ptr,  const char *group_key,
23       size_t group_key_length, const char  *key,  size_t  key_length,  size_t
24       *value_length, uint32_t *flags, memcached_return_t *error)
25
26       memcached_return_t  memcached_mget_by_key(memcached_st *ptr, const char
27       *group_key, size_t group_key_length, const  char  *const  *keys,  const
28       size_t *key_length, size_t number_of_keys)
29
30       memcached_return_t      memcached_fetch_execute(memcached_st      *ptr,
31       memcached_execute_fn *callback, void *context, uint32_t number_of_call‐
32       backs)
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34       memcached_return_t memcached_mget_execute(memcached_st *ptr, const char
35       *const  *keys,  const  size_t   *key_length,   size_t   number_of_keys,
36       memcached_execute_fn *callback, void *context, uint32_t number_of_call‐
37       backs)
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39       memcached_return_t   memcached_mget_execute_by_key(memcached_st   *ptr,
40       const  char  *group_key,  size_t  group_key_length,  const  char *const
41       *keys,    const    size_t    *key_length,    size_t     number_of_keys,
42       memcached_execute_fn *callback, void *context, uint32_t number_of_call‐
43       backs)
44
45       typedef memcached_return_t  (*memcached_execute_fn)(const  memcached_st
46       *ptr, memcached_result_st *result, void *context)
47

DESCRIPTION

49       memcached_get()  is  used to fetch an individual value from the server.
50       You must pass in a key and its length to fetch  the  object.  You  must
51       supply three pointer variables which will give you the state of the re‐
52       turned object.  A uint32_t pointer to contain whatever flags you stored
53       with  the  value, a size_t pointer which will be filled with size of of
54       the object, and a memcached_return_t pointer to hold any error. The ob‐
55       ject  will  be returned upon success and NULL will be returned on fail‐
56       ure. Any object returned by memcached_get() must  be  released  by  the
57       caller application.
58
59       memcached_mget()  is used to select multiple keys at once. For multiple
60       key operations it is always faster to use this function.  This function
61       always works asynchronously.
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63       To  retrieve data after a successful execution of memcached_mget(), you
64       will need to call memcached_fetch_result().   You  should  continue  to
65       call  this  function  until it returns a NULL (i.e. no more values). If
66       you need to quit in the middle of a memcached_mget() call, you can exe‐
67       cute a memcached_quit(), those this is not required.
68
69       memcached_fetch_result()  is used to fetch an individual value from the
70       server. memcached_mget()  must  always  be  called  before  using  this
71       method.  You must pass in a key and its length to fetch the object. You
72       must supply three pointer variables which will give you  the  state  of
73       the  returned object.  A uint32_t pointer to contain whatever flags you
74       stored with the value, a size_t pointer which will be filled with  size
75       of  of  the object, and a memcached_return_t pointer to hold any error.
76       The object will be returned upon success and NULL will be  returned  on
77       failure. MEMCACHED_END is returned by the *error value when all objects
78       that  have  been  found  have  been  returned.  The  final  value  upon
79       MEMCACHED_END is null.
80
81       memcached_fetch_result() is used to return a memcached_result_st struc‐
82       ture from a memcached server. The result object is  forward  compatible
83       with  changes  to  the server. For more information please refer to the
84       memcached_result_st help. This function will dynamically allocate a re‐
85       sult structure for you if you do not pass one to the function.
86
87       memcached_fetch_execute()  is a callback function for result sets.  In‐
88       stead of returning the results to you for processing, it passes each of
89       the  result sets to the list of functions you provide. It passes to the
90       function a memcached_st that can be cloned for use in the called  func‐
91       tion  (it  can not be used directly). It also passes a result set which
92       does not need to be freed. Finally it passes a "context". This is  just
93       a  pointer  to a memory reference you supply the calling function. Cur‐
94       rently only one value is being passed to each function call. In the fu‐
95       ture there will be an option to allow this to be an array.
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97       memcached_mget_execute() and memcached_mget_execute_by_key() is similar
98       to memcached_mget(), but it may trigger the supplied callbacks with re‐
99       sult sets while sending out the queries. If you try to perform a really
100       large multiget with memcached_mget() you may encounter  a  deadlock  in
101       the OS kernel (it will fail to write data to the socket because the in‐
102       put buffer is full). memcached_mget_execute() solves  this  problem  by
103       processing  some of the results before continuing sending out requests.
104       Please note that this function is only available in the  binary  proto‐
105       col.
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107       memcached_get_by_key()  and memcached_mget_by_key() behave in a similar
108       nature as memcached_get() and memcached_mget().  The difference is that
109       they take a master key that is used for determining which server an ob‐
110       ject was stored if key partitioning was used for storage.
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112       All   of   the   above   functions   are   not    tested    when    the
113       MEMCACHED_BEHAVIOR_USE_UDP  has  been set. Executing any of these func‐
114       tions with this behavior on will result in MEMCACHED_NOT_SUPPORTED  be‐
115       ing   returned,   or   for  those  functions  which  do  not  return  a
116       memcached_return_t,  the  error  function  parameter  will  be  set  to
117       MEMCACHED_NOT_SUPPORTED.
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RETURN VALUE

120       All  objects  retrieved  via  memcached_get() or memcached_get_by_key()
121       must be freed with free(3).
122
123       memcached_get() will return NULL on error.  You must look at the  value
124       of error to determine what the actual error was.
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126       memcached_fetch_execute()  return  MEMCACHED_SUCCESS  if  all keys were
127       successful. MEMCACHED_NOTFOUND will be returned if no keys at all  were
128       found.
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130       memcached_fetch_result()  sets  error  to MEMCACHED_END upon successful
131       conclusion.  MEMCACHED_NOTFOUND will be returned if no keys at all were
132       found.
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SEE ALSO

135       memcached(1) libmemcached(3) memcached_strerror(3)
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1401.1                              Nov 09, 2022          MEMCACHED_GET_BY_KEY(3)
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