1 .TH "MEMCACHED_REPLACE" "3" "May 23, 2011" "0.47" "libmemcached"
3 memcached_replace \- Storing and Replacing Data
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35 #include <libmemcached/memcached.h>
38 .B memcached_return_t memcached_set (memcached_st *ptr, const char *key, size_t key_length, const char *value, size_t value_length, time_t expiration, uint32_t flags);
42 .B memcached_return_t memcached_add (memcached_st *ptr, const char *key, size_t key_length, const char *value, size_t value_length, time_t expiration, uint32_t flags);
46 .B memcached_return_t memcached_replace (memcached_st *ptr, const char *key, size_t key_length, const char *value, size_t value_length, time_t expiration, uint32_t flags);
50 .B memcached_return_t memcached_set_by_key(memcached_st *ptr, const char *group_key, size_t group_key_length, const char *key, size_t key_length, const char *value, size_t value_length, time_t expiration, uint32_t flags);
54 .B memcached_return_t memcached_add_by_key(memcached_st *ptr, const char *group_key, size_t group_key_length, const char *key, size_t key_length, const char *value, size_t value_length, time_t expiration, uint32_t flags);
58 .B memcached_return_t memcached_replace_by_key(memcached_st *ptr, const char *group_key, size_t group_key_length, const char *key, size_t key_length, const char *value, size_t value_length, time_t expiration, uint32_t flags);
61 Compile and link with \-lmemcached
64 memcached_set(), memcached_add(), and memcached_replace() are all used to
65 store information on the server. All methods take a key, and its length to
66 store the object. Keys are currently limited to 250 characters when using either a version of memcached(1) which is 1.4 or below, or when using the text protocol.
67 You must supply both a value and a length. Optionally you
68 may test an expiration time for the object and a 16 byte value (it is
69 meant to be used as a bitmap). "flags" is a 4byte space that is stored alongside of the main value. Many sub libraries make use of this field, so in most cases users should avoid making use of it.
71 memcached_set() will write an object to the server. If an object already
72 exists it will overwrite what is in the server. If the object does not exist
73 it will be written. If you are using the non\-blocking mode this function
74 will always return true unless a network error occurs.
76 memcached_replace() replaces an object on the server. If the object is not
77 found on the server an error occurs.
79 memcached_add() adds an object to the server. If the object is found on the
80 server an error occurs, otherwise the value is stored.
82 memcached_cas() overwrites data in the server as long as the "cas" value is
83 still the same in the server. You can get the cas value of a result by
84 calling memcached_result_cas() on a memcached_result_st(3) structure. At the point
85 that this note was written cas is still buggy in memached. Turning on tests
86 for it in libmemcached(3) is optional. Please see memcached_set() for
87 information on how to do this.
89 memcached_set_by_key(), memcached_add_by_key(), and memcached_replace_by_key()
90 methods all behave in a similar method as the non key
91 methods. The difference is that they use their group_key parameter to map
92 objects to particular servers.
94 If you are looking for performance, memcached_set() with non\-blocking IO is
95 the fastest way to store data on the server.
97 All of the above functions are testsed with the \fBMEMCACHED_BEHAVIOR_USE_UDP\fPbehavior enabled. However, when using these operations with this behavior on, there
98 are limits to the size of the payload being sent to the server. The reason for
99 these limits is that the Memcached Server does not allow multi\-datagram requests
100 and the current server implementation sets a datagram size to 1400 bytes. Due
101 to protocol overhead, the actual limit of the user supplied data is less than
102 1400 bytes and depends on the protocol in use as, well as the operation being
103 executed. When running with the binary protocol, \(ga\(ga MEMCACHED_BEHAVIOR_BINARY_PROTOCOL\(ga\(ga,
104 the size of the key,value, flags and expiry combined may not exceed 1368 bytes.
105 When running with the ASCII protocol, the exact limit fluctuates depending on
106 which function is being executed and whether the function is a cas operation
107 or not. For non\-cas ASCII set operations, there are at least 1335 bytes available
108 to split among the key, key_prefix, and value; for cas ASCII operations there are
109 at least 1318 bytes available to split among the key, key_prefix and value. If the
110 total size of the command, including overhead, exceeds 1400 bytes, a \fBMEMCACHED_WRITE_FAILURE\fPwill be returned.
113 All methods return a value of type \fBmemcached_return_t\fP.
114 On success the value will be \fBMEMCACHED_SUCCESS\fP.
115 Use memcached_strerror() to translate this value to a printable string.
117 For memcached_replace() and memcached_add(), \fBMEMCACHED_NOTSTORED\fP is a
118 legitmate error in the case of a collision.
121 To find out more information please check:
122 \fI\%http://libmemcached.org/\fP
125 memcached(1) libmemached(3) memcached_strerror(3) memcached_prepend(3) memcached_cas(3) memcached_append(3)
129 2011, Brian Aker DataDifferential, http://datadifferential.com/
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