NAME
memcached_behavior_get, memcached_behavior_set - Manipulate behavior
LIBRARY
C Client Library for memcached (libmemcached, -lmemcached)
SYNOPSIS
#include <memcached.h>
uint64_t
memcached_behavior_get (memcached_st *ptr,
memcached_behavior flag);
memcached_return_t
memcached_behavior_set (memcached_st *ptr,
memcached_behavior flag,
uint64_t data);
DESCRIPTION
libmemcached(3) behavior can be modified by use
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 supported 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_value_fetch().
All other operations are supported 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).
MEMCACHED_BEHAVIOR_HASH
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
support 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
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 support.
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 pointer must be passed to
memcached_behavior_set() to change this value. For
memcached_behavior_get() a signed int value will be cast and
returned as the unsigned long long.
MEMCACHED_BEHAVIOR_USER_DATA
This allows you to store a pointer to a specifc piece of data. This
can be retrieved from inside of memcached_fetch_execute(). Cloning
a memcached_st
will copy the pointer to the clone. This was deprecated in 0.14 in
favor of memcached_callback_set(3). This will be removed in 0.15.
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.
MEMCACHED_BEHAVIOR_CORK
Enable TCP_CORK behavior. This is only available as an option
Linux. MEMCACHED_NO_SERVERS is returned if no servers are
available to test with. MEMCACHED_NOT_SUPPORTED is returned if we
were not able to determine if support was available. All other
responses then MEMCACHED_SUCCESS report an error of some sort. This
behavior also enables MEMCACHED_BEHAVIOR_TCP_NODELAY when set.
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.
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.
MEMCACHED_BEHAVIOR_SERVER_FAILURE_LIMIT
This number of times a host can have an error before it is
disabled.
MEMCACHED_BEHAVIOR_AUTO_EJECT_HOSTS
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_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.
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:
<https://launchpad.net/libmemcached>
AUTHOR
Brian Aker, <brian@tangent.org>
SEE ALSO
memcached(1) libmemcached(3) memcached_strerror(3)
2010-04-06 memcached_behavior_get.pop(3)