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..::docs::memcached_behavior(3) libmemcached ..::docs::memcached_behavior(3)

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
    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.

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.

Causes libmemcached(3) to use asychronous IO. This is the fastest transport available for storage functions.
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.
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.
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 dont know or dont 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.
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 can cache named lookups so that DNS lookups are made only once.
Support CAS operations (this is not enabled by default at this point in the server since it imposes a slight performance penalty).
Sets the default distribution to MEMCACHED_DISTRIBUTION_CONSISTENT_KETAMA and the hash to MEMCACHED_HASH_MD5.
Sets the default distribution to MEMCACHED_DISTRIBUTION_CONSISTENT_KETAMA with the weighted support. and the hash to MEMCACHED_HASH_MD5.
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.
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.
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.

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.
Enabling this will cause libmemcached(3) to test all keys to verify that they are valid keys.
Enabling this will cause hosts that are added to be placed in the host list in sorted order. This will defeat consisten hashing.
In non-blocking mode this changes the value of the timeout during socket connection.
Enable the use of the binary protocol. Please note that you cannot toggle this flag on an open connection.
Set this value to enable the server be removed after continuous MEMCACHED_BEHAVIOR_SERVER_FAILURE_LIMIT times connection failure.
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).
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).
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.
Set this value to specify that you really don't care about the result from your storage commands (set, add, replace, append, prepend).
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).

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://tangent.org/552/libmemcached.html>

AUTHOR

Brian Aker, <brian@tangent.org>

SEE ALSO

memcached(1) libmemcached(3) memcached_strerror(3)

2009-06-27