1MEMCACHED_REPLACE(3) libmemcached MEMCACHED_REPLACE(3)
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6 memcached_replace - Storing and Replacing Data
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9 #include <libmemcached/memcached.h>
10 memcached_return_t memcached_set(memcached_st *ptr, const char *key,
12 size_t key_length, const char *value, size_t value_length, time_t expi‐
13 ration, uint32_t flags)
14 memcached_return_t memcached_add(memcached_st *ptr, const char *key,
16 size_t key_length, const char *value, size_t value_length, time_t expi‐
17 ration, uint32_t flags)
18 memcached_return_t memcached_replace(memcached_st *ptr, const
20 char *key, size_t key_length, const char *value, size_t value_length,
21 time_t expiration, uint32_t flags)
22 memcached_return_t memcached_set_by_key(memcached_st *ptr, const
24 char *group_key, size_t group_key_length, const char *key,
25 size_t key_length, const char *value, size_t value_length, time_t expi‐
26 ration, uint32_t flags)
27 memcached_return_t memcached_add_by_key(memcached_st *ptr, const
29 char *group_key, size_t group_key_length, const char *key,
30 size_t key_length, const char *value, size_t value_length, time_t expi‐
31 ration, uint32_t flags)
32 memcached_return_t memcached_replace_by_key(memcached_st *ptr, const
34 char *group_key, size_t group_key_length, const char *key,
35 size_t key_length, const char *value, size_t value_length, time_t expi‐
36 ration, uint32_t flags)
37 Compile and link with -lmemcached
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41 memcached_set(), memcached_add(), and memcached_replace() are all used
42 to store information on the server. All methods take a key, and its
43 length to store the object. Keys are currently limited to 250 charac‐
44 ters when using either a version of memcached(1) which is 1.4 or below,
45 or when using the text protocol. You must supply both a value and a
46 length. Optionally you store the object. Keys are currently limited to
47 250 characters by the memcached(1) server. You must supply both a value
48 and a length. Optionally you may test an expiration time for the object
49 and a 16 byte value (it is meant to be used as a bitmap). "flags" is a
50 4byte space that is stored alongside of the main value. Many sub
51 libraries make use of this field, so in most cases users should avoid
52 making use of it.
53 memcached_set() will write an object to the server. If an object
55 already exists it will overwrite what is in the server. If the object
56 does not exist it will be written. If you are using the non-blocking
57 mode this function will always return true unless a network error
58 occurs.
59 memcached_replace() replaces an object on the server. If the object is
61 not found on the server an error occurs.
62 memcached_add() adds an object to the server. If the object is found on
64 the server an error occurs, otherwise the value is stored.
65 memcached_cas() overwrites data in the server as long as the "cas"
67 value is still the same in the server. You can get the cas value of a
68 result by calling memcached_result_cas() on a memcached_result_st(3)
69 structure. At the point that this note was written cas is still buggy
70 in memached. Turning on tests for it in libmemcached(3) is optional.
71 Please see memcached_set for information on how to do this.
72 memcached_set_by_key(), memcached_add_by_key(), and
74 memcached_replace_by_key() methods all behave in a similar method as
75 the non key methods. The difference is that they use their group_key
76 parameter to map objects to particular servers.
77 If you are looking for performance, memcached_set() with non-blocking
79 IO is the fastest way to store data on the server.
80 All of the above functions are testsed with the MEMCACHED_BEHAV‐
82 IOR_USE_UDP behavior enabled. However, when using these operations with
83 this behavior on, there are limits to the size of the payload being
84 sent to the server. The reason for these limits is that the Memcached
85 Server does not allow multi-datagram requests and the current server
86 implementation sets a datagram size to 1400 bytes. Due to protocol
87 overhead, the actual limit of the user supplied data is less than 1400
88 bytes and depends on the protocol in use as, well as the operation
89 being executed. When running with the binary protocol, MEMCACHED_BEHAV‐
90 IOR_BINARY_PROTOCOL, the size of the key,value, flags and expiry com‐
91 bined may not exceed 1368 bytes. When running with the ASCII protocol,
92 the exact limit fluctuates depending on which function is being exe‐
93 cuted and whether the function is a cas operation or not. For non-cas
94 ASCII set operations, there are at least 1335 bytes available to split
95 among the key, key_prefix, and value; for cas ASCII operations there
96 are at least 1318 bytes available to split among the key, key_prefix
97 and value. If the total size of the command, including overhead,
98 exceeds 1400 bytes, a MEMCACHED_WRITE_FAILURE will be returned.
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101 All methods return a value of type memcached_return_t. On success the
102 value will be MEMCACHED_SUCCESS. Use memcached_strerror() to translate
103 this value to a printable string.
104 For memcached_replace() and memcached_add(), MEMCACHED_NOTSTORED is a
106 legitmate error in the case of a collision.
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109 To find out more information please check: http://libmemcached.org/
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112 memcached(1) libmemached(3) memcached_strerror(3) memcached_prepend(3)
113 memcached_cas(3) memcached_append(3)
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116 Brian Aker
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119 2011-2013, Brian Aker DataDifferential, http://datadifferential.com/
1201.0.16 January 31, 2013 MEMCACHED_REPLACE(3)