[m6w6/libmemcached] / docs / memcached_behavior.rst

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Modifying how the driver behaves
================================


Manipulate behavior


*******
LIBRARY
*******


C Client Library for memcached (libmemcached, -lmemcached)


--------
SYNOPSIS
--------



.. code-block:: perl

   #include <libmemcached/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 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_value_fetch().
 
 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).
 


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 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
 
 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 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 tests 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. 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
 
 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.
 


MEMCACHED_BEHAVIOR_HASH_WITH_PREFIX_KEY
 
 When enabled the prefix key will be added to the key when determining
 server by hash.
 



******
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 <https://launchpad.net/libmemcached>`_


******
AUTHOR
******


Brian Aker, <brian@tangent.org>


--------
SEE ALSO
--------


:manpage:`memcached(1)` :manpage:`libmemcached(3)` :manpage:`memcached_strerror(3)`