--- name: "Memcached::libmemcached::memcached_behavior" section: "3pm" platform: "linux" package: "libmemcached-libmemcached-perl" version: "1.001801+dfsg-5+b2" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/Memcached::libmemcached::memcached_behavior" --- # Memcached::libmemcached::memcached\_behavior(3pm) Manipulate behavior ## NAME memcached\_behavior\_get, memcached\_behavior\_set - Manipulate behavior ## LIBRARY C Client Library for memcached (libmemcached, -lmemcached) ## SYNOPSIS ``` #include 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)](/libmemcached/3.md) 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)](/libmemcached/3.md) 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)](/libmemcached/3.md) 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)](/libmemcached/3.md) 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)](/memcached_callback_set/3.md). 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)](/libmemcached/3.md) 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 occurred 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 occurred 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: \ ## AUTHOR Brian Aker, \ ## SEE ALSO [**memcached**(1)](/memcached/1.md) [**libmemcached**(3)](/libmemcached/3.md) [**memcached\_strerror**(3)](/memcached_strerror/3.md)