git.m6w6.name Git - awesomized/libmemcached/blob - docs/memcached_cas.rst

   1 ====================================================
   2 Working with data on the server in an atomic fashion
   3 ====================================================
   4
   5 .. index:: object: memcached_st
   6
   7
   8 --------
   9 SYNOPSIS
  10 --------
  11
  12
  13 #include <libmemcached/memcached.h>
  14
  15 .. c:function:: memcached_return_t memcached_cas(memcached_st *ptr, const char *key, size_t key_length, const char *value, size_t value_length, time_t expiration, uint32_t flags, uint64_t cas);
  16
  17 .. c:function:: memcached_return_t memcached_cas_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, uint64_t cas);
  18
  19 Compile and link with -lmemcached
  20
  21
  22 -----------
  23 DESCRIPTION
  24 -----------
  25
  26 memcached_cas() overwrites data in the server as long as the "cas" value is
  27 still the same in the server. You can get the cas value of a result by
  28 calling memcached_result_cas() on a memcached_result_st(3) structure. At the point
  29 that this note was written cas is still buggy in memached. Turning on tests
  30 for it in libmemcached(3) is optional. Please see memcached_set() for
  31 information on how to do this.
  32
  33 memcached_cas_by_key() method behaves in a similar method as the non key
  34 methods. The difference is that it uses the group_key parameter to map
  35 objects to particular servers.
  36
  37 memcached_cas() is testsed with the \ ``MEMCACHED_BEHAVIOR_USE_UDP``\
  38 behavior enabled. However, when using these operations with this behavior on, there
  39 are limits to the size of the payload being sent to the server.  The reason for
  40 these limits is that the Memcached Server does not allow multi-datagram requests
  41 and the current server implementation sets a datagram size to 1400 bytes. Due
  42 to protocol overhead, the actual limit of the user supplied data is less than
  43 1400 bytes and depends on the protocol in use as, well as the operation being
  44 executed. When running with the binary protocol, \ `` MEMCACHED_BEHAVIOR_BINARY_PROTOCOL``\ ,
  45 the size of the key,value, flags and expiry combined may not exceed 1368 bytes.
  46 When running with the ASCII protocol, the exact limit fluctuates depending on
  47 which function is being executed and whether the function is a cas operation
  48 or not. For non-cas ASCII set operations, there are at least 1335 bytes available
  49 to split among the key, key_prefix, and value; for cas ASCII operations there are
  50 at least 1318 bytes available to split among the key, key_prefix and value. If the
  51 total size of the command, including overhead, exceeds 1400 bytes, a \ ``MEMCACHED_WRITE_FAILURE``\
  52 will be returned.
  53
  54
  55 ------
  56 RETURN
  57 ------
  58
  59
  60 All methods return a value of type \ ``memcached_return_t``\ .
  61 On success the value will be \ ``MEMCACHED_SUCCESS``\ .
  62 Use memcached_strerror() to translate this value to a printable string.
  63
  64
  65 ----
  66 HOME
  67 ----
  68
  69
  70 To find out more information please check:
  71 `http://libmemcached.org/ <http://libmemcached.org/>`_
  72
  73
  74 --------
  75 SEE ALSO
  76 --------
  77
  78
  79 memcached(1) libmemached(3) memcached_strerror(3) memcached_set(3) memcached_append(3) memcached_add(3) memcached_prepend(3) memcached_replace(3)
  80