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

   1 Working with data on the server in an atomic fashion
   2 ====================================================
   3
   4 SYNOPSIS
   5 --------
   6
   7 #include <libmemcached/memcached.h>
   8   Compile and link with -lmemcached
   9
  10 .. 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)
  11
  12 .. 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)
  13
  14     :param ptr: pointer to an initialized `memcached_st` struct
  15     :param group_key: key namespace
  16     :param group_key_length: length of the `group_key` without any trailing zero
  17     :param key: the key to check
  18     :param key_length: the length of the `key` without any trailing zero
  19     :param value: the value to set
  20     :param value_length: the length of the `value` without any trailing zero
  21     :param expiration: expiration time as unix timestamp or relative time in seconds
  22     :param flags: 16 bit flags
  23     :param cas: the ``cas`` value to compare
  24     :returns: `memcached_return_t` indicating success
  25
  26 DESCRIPTION
  27 -----------
  28
  29 `memcached_cas` overwrites data in the server as long as the ``cas`` value is
  30 still the same in the server. You can get the ``cas`` value of a result by
  31 calling `memcached_result_cas` on a `memcached_result_st` structure.
  32
  33 `memcached_cas_by_key` method behaves in a similar way as the non key methods.
  34 The difference is that it uses the ``group_key`` parameter to map objects to
  35 particular servers.
  36
  37 `memcached_cas` is tested with the `MEMCACHED_BEHAVIOR_USE_UDP` behavior
  38 enabled. However, when using these operations with this behavior on, there are
  39 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 to
  42 protocol overhead, the actual limit of the user supplied data is less than 1400
  43 bytes and depends on the protocol in use as, well as the operation being
  44 executed. When running with the binary protocol,
  45 `MEMCACHED_BEHAVIOR_BINARY_PROTOCOL`, the size of the key,value, flags and
  46 expiry combined may not exceed 1368 bytes. When running with the ASCII protocol,
  47 the exact limit fluctuates depending on which function is being executed and
  48 whether the function is a cas operation or not. For non-cas ASCII set
  49 operations, there are at least 1335 bytes available to split among the key,
  50 key_prefix, and value; for cas ASCII operations there are at least 1318 bytes
  51 available to split among the key, key_prefix and value. If the total size of the
  52 command, including overhead, exceeds 1400 bytes, a `MEMCACHED_WRITE_FAILURE`
  53 will be returned.
  54
  55 RETURN VALUE
  56 ------------
  57
  58 All methods return a value of type `memcached_return_t`.
  59 On success the value will be `MEMCACHED_SUCCESS`.
  60 Use `memcached_strerror` to translate this value to a printable
  61 string.
  62
  63 SEE ALSO
  64 --------
  65
  66 .. only:: man
  67
  68     :manpage:`memcached(1)`
  69     :manpage:`libmemcached(3)`
  70     :manpage:`memcached_strerror(3)`
  71     :manpage:`memcached_set(3)`
  72     :manpage:`memcached_append(3)`
  73     :manpage:`memcached_add(3)`
  74     :manpage:`memcached_prepend(3)`
  75     :manpage:`memcached_replace(3)`
  76
  77 .. only:: html
  78
  79     * :manpage:`memcached(1)`
  80     * :doc:`../libmemcached`
  81     * :doc:`memcached_set`
  82     * :doc:`memcached_append`
  83     * :doc:`memcached_strerror`