memcached_cas(3)

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

6       memcached_cas - Atomic Compare and Swap
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SYNOPSIS

9       #include <libmemcached/memcached.h>
10              Compile and link with -lmemcached
11
12       memcached_return_t  memcached_cas(memcached_st  *ptr,  const char *key,
13       size_t key_length, const char *value, size_t value_length, time_t expi‐
14       ration, uint32_t flags, uint64_t cas)
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16       memcached_return_t  memcached_cas_by_key(memcached_st  *ptr, const char
17       *group_key,  size_t   group_key_length,   const   char   *key,   size_t
18       key_length,  const char *value, size_t value_length, time_t expiration,
19       uint32_t flags, uint64_t cas)
20
21              Parameters
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23                     • ptr -- pointer to an initialized memcached_st struct
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25                     • group_key -- key namespace
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27                     • group_key_length -- length of the group_key without any
28                       trailing zero
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30                     • key -- the key to check
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32                     • key_length  -- the length of the key without any trail‐
33                       ing zero
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35                     • value -- the value to set
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37                     • value_length -- the length of  the  value  without  any
38                       trailing zero
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40                     • expiration -- expiration time as unix timestamp or rel‐
41                       ative time in seconds
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43                     • flags -- 16 bit flags
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45                     • cas -- the cas value to compare
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47              Returns
48                     memcached_return_t indicating success
49

DESCRIPTION

51       memcached_cas() overwrites data in the server as long as the cas  value
52       is  still the same in the server. You can get the cas value of a result
53       by calling memcached_result_cas() on a memcached_result_st structure.
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55       memcached_cas_by_key() method behaves in a similar way as the  non  key
56       methods.  The difference is that it uses the group_key parameter to map
57       objects to particular servers.
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59       memcached_cas() is tested with the MEMCACHED_BEHAVIOR_USE_UDP  behavior
60       enabled.  However,  when  using these operations with this behavior on,
61       there are limits to the size of the payload being sent to  the  server.
62       The reason for these limits is that the Memcached Server does not allow
63       multi-datagram requests and the current server  implementation  sets  a
64       datagram size to 1400 bytes. Due to protocol overhead, the actual limit
65       of the user supplied data is less than 1400 bytes and  depends  on  the
66       protocol  in use as, well as the operation being executed. When running
67       with the binary protocol, MEMCACHED_BEHAVIOR_BINARY_PROTOCOL, the  size
68       of  the key,value, flags and expiry combined may not exceed 1368 bytes.
69       When running with the ASCII protocol, the exact  limit  fluctuates  de‐
70       pending on which function is being executed and whether the function is
71       a cas operation or not. For non-cas ASCII set operations, there are  at
72       least  1335  bytes  available  to  split among the key, key_prefix, and
73       value; for cas ASCII operations there are at least 1318 bytes available
74       to  split among the key, key_prefix and value. If the total size of the
75       command,    including    overhead,    exceeds     1400     bytes,     a
76       MEMCACHED_WRITE_FAILURE will be returned.
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RETURN VALUE

79       All  methods return a value of type memcached_return_t.  On success the
80       value will be MEMCACHED_SUCCESS.  Use memcached_strerror() to translate
81       this value to a printable string.
82

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

SEE ALSO