Working with data on the server in an atomic fashion¶
SYNOPSIS¶
- #include <libmemcached/memcached.h>
Compile and link with -lmemcached
-
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)¶
-
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)¶ - Parameters
ptr -- pointer to an initialized
memcached_st
structgroup_key -- key namespace
group_key_length -- length of the
group_key
without any trailing zerokey -- the key to check
key_length -- the length of the
key
without any trailing zerovalue -- the value to set
value_length -- the length of the
value
without any trailing zeroexpiration -- expiration time as unix timestamp or relative time in seconds
flags -- 16 bit flags
cas -- the
cas
value to compare
- Returns
memcached_return_t
indicating success
DESCRIPTION¶
memcached_cas()
overwrites data in the server as long as the cas
value is
still the same in the server. You can get the cas
value of a result by
calling memcached_result_cas()
on a memcached_result_st
structure.
memcached_cas_by_key()
method behaves in a similar way as the non key methods.
The difference is that it uses the group_key
parameter to map objects to
particular servers.
memcached_cas()
is tested with the MEMCACHED_BEHAVIOR_USE_UDP
behavior
enabled. However, when using these operations with this behavior on, there are
limits to the size of the payload being sent to the server. The reason for
these limits is that the Memcached Server does not allow multi-datagram requests
and the current server implementation sets a datagram size to 1400 bytes. Due to
protocol overhead, the actual limit of the user supplied data is less than 1400
bytes and depends on the protocol in use as, well as the operation being
executed. When running with the binary protocol,
MEMCACHED_BEHAVIOR_BINARY_PROTOCOL
, the size of the key,value, flags and
expiry combined may not exceed 1368 bytes. When running with the ASCII protocol,
the exact limit fluctuates depending on which function is being executed and
whether the function is a cas operation or not. For non-cas ASCII set
operations, there are at least 1335 bytes available to split among the key,
key_prefix, and value; for cas ASCII operations there are at least 1318 bytes
available to split among the key, key_prefix and value. If the total size of the
command, including overhead, exceeds 1400 bytes, a MEMCACHED_WRITE_FAILURE
will be returned.
RETURN VALUE¶
All methods return a value of type memcached_return_t
.
On success the value will be MEMCACHED_SUCCESS
.
Use memcached_strerror()
to translate this value to a printable
string.