NAME¶
memcached_behavior_get - libmemcached Documentation
Manipulate the behavior of a memcached_st structure.
SYNOPSIS¶
#include <libmemcached/memcached.h>
- uint64_t
memcached_behavior_get(memcached_st *ptr,
memcached_behavior_t flag)
- memcached_return_t
memcached_behavior_set(memcached_st *ptr,
memcached_behavior_t flag,
uint64_t data)
Compile and link with -lmemcached
DESCRIPTION¶
libmemcached(3) behavior can be modified by using
memcached_behavior_set(). Default behavior is the library strives to be
quick and accurate. Some behavior, while being faster, can also result in not
entirely accurate behavior (for instance,
memcached_set() will always
respond with
MEMCACHED_SUCCESS).
memcached_behavior_get() takes a behavior flag and returns whether or not
that behavior is currently enabled in the client.
memcached_behavior_set() changes the value of a particular option of the
client. It takes both a flag (listed below) and a value. For simple on or off
options you just need to pass in a value of 1. Calls to
memcached_behavior_set() will flush and reset all connections.
- MEMCACHED_BEHAVIOR_USE_UDP
Causes
libmemcached(3) to use the UDP transport when communicating with a
memcached server. Not all I/O operations are testsed when this behavior is
enababled. The following operations will return
MEMCACHED_NOT_SUPPORTED
when executed with the
MEMCACHED_BEHAVIOR_USE_UDP enabled:
memcached_version(),
memcached_stat(),
memcached_get(),
memcached_get_by_key(),
memcached_mget(),
memcached_mget_by_key(),
memcached_fetch(),
memcached_fetch_result(),
memcached_fetch_execute().
All other operations are testsed but are executed in a 'fire-and-forget' mode,
in which once the client has executed the operation, no attempt will be made
to ensure the operation has been received and acted on by the server.
libmemcached(3) does not allow TCP and UDP servers to be shared within
the same libmemached(3) client 'instance'. An attempt to add a TCP server when
this behavior is enabled will result in a
MEMCACHED_INVALID_HOST_PROTOCOL, as will attempting to add a UDP server
when this behavior has not been enabled.
- MEMCACHED_BEHAVIOR_NO_BLOCK
Causes
libmemcached(3) to use asychronous IO. This is the fastest
transport available for storage functions.
- MEMCACHED_BEHAVIOR_SND_TIMEOUT
This sets the microsecond behavior of the socket against the SO_SNDTIMEO flag.
In cases where you cannot use non-blocking IO this will allow you to still
have timeouts on the sending of data.
- MEMCACHED_BEHAVIOR_RCV_TIMEOUT
This sets the microsecond behavior of the socket against the SO_RCVTIMEO flag.
In cases where you cannot use non-blocking IO this will allow you to still have
timeouts on the reading of data.
- MEMCACHED_BEHAVIOR_TCP_NODELAY
Turns on the no-delay feature for connecting sockets (may be faster in some
environments).
Makes the default hashing algorithm for keys use MD5. The value can be set to
either
MEMCACHED_HASH_DEFAULT,
MEMCACHED_HASH_MD5,
MEMCACHED_HASH_CRC,
MEMCACHED_HASH_FNV1_64,
MEMCACHED_HASH_FNV1A_64,
MEMCACHED_HASH_FNV1_32,
MEMCACHED_HASH_FNV1A_32,
MEMCACHED_HASH_JENKINS,
MEMCACHED_HASH_HSIEH, and
MEMCACHED_HASH_MURMUR.
Each hash has it's advantages and it's weaknesses. If you don't know or don't
care, just go with the default.
Support for
MEMCACHED_HASH_HSIEH is a compile time option that is
disabled by default. To enable tests for this hashing algorithm, configure and
build libmemcached with the --enable-hash_hsieh.
- MEMCACHED_BEHAVIOR_DISTRIBUTION
Using this you can enable different means of distributing values to servers.
The default method is MEMCACHED_DISTRIBUTION_MODULA. You can enable consistent
hashing by setting MEMCACHED_DISTRIBUTION_CONSISTENT. Consistent hashing
delivers better distribution and allows servers to be added to the cluster
with minimal cache losses. Currently MEMCACHED_DISTRIBUTION_CONSISTENT is an
alias for the value MEMCACHED_DISTRIBUTION_CONSISTENT_KETAMA.
- MEMCACHED_BEHAVIOR_CACHE_LOOKUPS
Deprecated since version 0.46(?): DNS lookups are now always cached until an
error occurs with the server.
Memcached can cache named lookups so that DNS lookups are made only once.
- MEMCACHED_BEHAVIOR_SUPPORT_CAS
Support CAS operations (this is not enabled by default at this point in the
server since it imposes a slight performance penalty).
- MEMCACHED_BEHAVIOR_KETAMA
Sets the default distribution to MEMCACHED_DISTRIBUTION_CONSISTENT_KETAMA and
the hash to
MEMCACHED_HASH_MD5.
- MEMCACHED_BEHAVIOR_KETAMA_WEIGHTED
- Sets the default distribution to
MEMCACHED_DISTRIBUTION_CONSISTENT_KETAMA with the weighted tests. and the
hash to MEMCACHED_HASH_MD5.
- MEMCACHED_BEHAVIOR_KETAMA_HASH
Sets the hashing algorithm for host mapping on continuum. The value can be set
to either
MEMCACHED_HASH_DEFAULT,
MEMCACHED_HASH_MD5,
MEMCACHED_HASH_CRC,
MEMCACHED_HASH_FNV1_64,
MEMCACHED_HASH_FNV1A_64,
MEMCACHED_HASH_FNV1_32, and
MEMCACHED_HASH_FNV1A_32.
- MEMCACHED_BEHAVIOR_KETAMA_COMPAT
Sets the compatibility mode. The value can be set to either
MEMCACHED_KETAMA_COMPAT_LIBMEMCACHED (this is the default) or
MEMCACHED_KETAMA_COMPAT_SPY to be compatible with the SPY Memcached client for
Java.
- MEMCACHED_BEHAVIOR_POLL_TIMEOUT
Modify the timeout value that is used by poll. The default value is -1. An
signed int must be passed to memcached_behavior_set to change this value (this
requires casting). For memcached_behavior_get a signed int value will be cast
and returned as the unsigned long long.
- MEMCACHED_BEHAVIOR_USER_DATA
Deprecated since version <: 0.30
- MEMCACHED_BEHAVIOR_BUFFER_REQUESTS
Enabling buffered IO causes commands to "buffer" instead of being
sent. Any action that gets data causes this buffer to be be sent to the remote
connection. Quiting the connection or closing down the connection will also
cause the buffered data to be pushed to the remote connection.
- MEMCACHED_BEHAVIOR_VERIFY_KEY
Enabling this will cause
libmemcached(3) to test all keys to verify that
they are valid keys.
- MEMCACHED_BEHAVIOR_SORT_HOSTS
Enabling this will cause hosts that are added to be placed in the host list in
sorted order. This will defeat consisten hashing.
- MEMCACHED_BEHAVIOR_CONNECT_TIMEOUT
In non-blocking mode this changes the value of the timeout during socket
connection.
- MEMCACHED_BEHAVIOR_BINARY_PROTOCOL
Enable the use of the binary protocol. Please note that you cannot toggle this
flag on an open connection.
- MEMCACHED_BEHAVIOR_SERVER_FAILURE_LIMIT
Set this value to enable the server be removed after continuous
MEMCACHED_BEHAVIOR_SERVER_FAILURE_LIMIT times connection failure.
- MEMCACHED_BEHAVIOR_IO_MSG_WATERMARK
Set this value to tune the number of messages that may be sent before
libmemcached should start to automatically drain the input queue. Setting this
value to high, may cause libmemcached to deadlock (trying to send data, but
the send will block because the input buffer in the kernel is full).
- MEMCACHED_BEHAVIOR_IO_BYTES_WATERMARK
Set this value to tune the number of bytes that may be sent before libmemcached
should start to automatically drain the input queue (need at least 10 IO
requests sent without reading the input buffer). Setting this value to high,
may cause libmemcached to deadlock (trying to send data, but the send will
block because the input buffer in the kernel is full).
- MEMCACHED_BEHAVIOR_IO_KEY_PREFETCH
The binary protocol works a bit different than the textual protocol in that a
multiget is implemented as a pipe of single get-operations which are sent to
the server in a chunk. If you are using large multigets from your application,
you may improve the latency of the gets by setting this value so you send out
the first chunk of requests when you hit the specified limit. It allows the
servers to start processing the requests to send the data back while the rest
of the requests are created and sent to the server.
- MEMCACHED_BEHAVIOR_NOREPLY
Set this value to specify that you really don't care about the result from your
storage commands (set, add, replace, append, prepend).
- MEMCACHED_BEHAVIOR_NUMBER_OF_REPLICAS
If you just want "a poor mans HA", you may specify the numbers of
replicas libmemcached should store of each item (on different servers). This
replication does not dedicate certain memcached servers to store the replicas
in, but instead it will store the replicas together with all of the other
objects (on the 'n' next servers specified in your server list).
- MEMCACHED_BEHAVIOR_RANDOMIZE_REPLICA_READ
Allows randomizing the replica reads starting point. Normally the read is done
from primary server and in case of miss the read is done from primary + 1,
then primary + 2 all the way to 'n' replicas. If this option is set on the
starting point of the replica reads is randomized between the servers. This
allows distributing read load to multiple servers with the expense of more
write traffic.
This open has been deprecated with the behavior now built and used appropriately
on selected platforms.
- MEMCACHED_BEHAVIOR_KEEPALIVE
Enable TCP_KEEPALIVE behavior.
- MEMCACHED_BEHAVIOR_KEEPALIVE_IDLE
Specify time, in seconds, to mark a connection as idle. This is only available
as an option Linux.
- MEMCACHED_BEHAVIOR_SOCKET_SEND_SIZE
Find the current size of SO_SNDBUF. A value of 0 means either an error occured
or no hosts were available. It is safe to assume system default if this
occurs. If an error occurs you can checked the last cached errno statement to
find the specific error.
- MEMCACHED_BEHAVIOR_SOCKET_RECV_SIZE
Find the current size of SO_RCVBUF. A value of 0 means either an error occured
or no hosts were available. It is safe to assume system default if this
occurs. If an error occurs you can checked the last cached errno statement to
find the specific error.
- MEMCACHED_BEHAVIOR_SERVER_FAILURE_LIMIT
Deprecated since version 0.48: See
MEMCACHED_BEHAVIOR_REMOVE_FAILED_SERVERS
This number of times a host can have an error before it is disabled.
- MEMCACHED_BEHAVIOR_AUTO_EJECT_HOSTS
Deprecated since version 0.48: See
MEMCACHED_BEHAVIOR_REMOVE_FAILED_SERVERS
If enabled any hosts which have been flagged as disabled will be removed from
the list of servers in the memcached_st structure. This must be used in
combination with MEMCACHED_BEHAVIOR_SERVER_FAILURE_LIMIT.
- MEMCACHED_BEHAVIOR_REMOVE_FAILED_SERVERS
- If enabled any hosts which have been flagged as disabled
will be removed from the list of servers in the memcached_st
structure.
- MEMCACHED_BEHAVIOR_RETRY_TIMEOUT
When enabled a host which is problematic will only be checked for usage based on
the amount of time set by this behavior. The value is in seconds.
- MEMCACHED_BEHAVIOR_HASH_WITH_PREFIX_KEY
When enabled the prefix key will be added to the key when determining server by
hash. See
MEMCACHED_CALLBACK_NAMESPACE for additional information.
RETURN¶
memcached_behavior_get returns either the current value of the get, or 0 or 1 on
simple flag behaviors (1 being enabled). memcached_behavior_set returns
failure or success.
NOTES¶
memcached_behavior_set in version .17 was changed from taking a pointer to data
value, to taking a uin64_t.
HOME¶
To find out more information please check:
http://libmemcached.org/
SEE ALSO¶
memcached(1) libmemcached(3) memcached_strerror(3)
AUTHOR¶
Brian Aker
COPYRIGHT¶
2011, Brian Aker DataDifferential,
http://datadifferential.com/