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MEMCACHED_BEHAVIOR(3) libmemcached-awesome MEMCACHED_BEHAVIOR(3)

NAME

memcached_behavior - libmemcached Documentation

Manipulate the behavior of a memcached_st structure.

SYNOPSIS

#include <libmemcached/memcached.h>
Compile and link with -lmemcached

  • ptr -- pointer to initialized memcached_st struct
  • flag -- memcached_behavior_t to query

the vaue set for flag


  • ptr -- pointer to initialized memcached_st struct
  • flag -- memcached_behavior_t to set
  • data -- the value to set for flag

memcached_return_t indicating success

Changed in version 0.17: The data argument of memcached_behavior_set() was changed from taking a pointer to data value, to taking a uin64_t.



Causes libmemcached to use the UDP transport when communicating with a memcached server. Not all I/O operations are tested when this behavior is enabled.

The following operations will return MEMCACHED_NOT_SUPPORTED when executed with 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 tested 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 does not allow TCP and UDP servers to be shared within the same libmemcached 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.


This enables SO_LINGER only, so the close(2) call on the socket returns immediately. I/O is always handled asynchronously in recent versions of libmemcached.

This sets the microsecond behavior of the socket against the SO_SNDTIMEO flag.

This sets the microsecond behavior of the socket against the SO_RCVTIMEO flag.

Disables Nagle's algorithm. See RFC 896.

Set the hash algorithm used for keys.

Each hash has its advantages and its weaknesses. If you don't know or don't care, just go with the default.


Setting a memcached_server_distribution_t you can enable different means of distributing values to servers.

The default method is MEMCACHED_DISTRIBUTION_MODULA (hash of the key modulo number of servers).

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.


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.


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 tests. Makes the default hashing algorithm for keys use MEMCACHED_HASH_MD5.

Sets the hashing algorithm for host mapping on continuum.

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.

Modify the timeout in milliseconds 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 'unsigned long long'.

Deprecated since version <: 0.30


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 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 consistent hashing.

Set the timeout during socket connection in milliseconds. Specifying -1 means an infinite time‐out.

Enable the use of the binary protocol. Please note that you cannot toggle this flag on an open connection.

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).

Specify the number 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).

Requires the binary protocol and only supports (M)GET/SET/DELETE.

NOTE: libmemcached does not guarantee nor enforce any consistency.


Allows randomizing the replica reads starting point. Normally the read is done from primary server and in case of failure the read is done from primary + 1, then primary + 2 all the way to 'n' replicas.

This allows distributing read load to multiple servers with the expense of more write traffic.

NOTE: Only errors to communicate with a server are considered failures, so MEMCACHED_NOTFOUND does not account for failure.


Deprecated since version ?: This option has been deprecated with the behavior now built in and used appropriately on selected platforms.


Enable TCP_KEEPALIVE behavior.

Specify time, in seconds, to mark a connection as idle. This is only available as an option on Linux.

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.

If an error occurs you can check the last cached errno to find the specific error.


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.

If an error occurs you can check the last cached errno to find the specific error.


Deprecated since version 0.48: See MEMCACHED_BEHAVIOR_REMOVE_FAILED_SERVERS

Set this value to enable the server be removed after continuous MEMCACHED_BEHAVIOR_SERVER_FAILURE_LIMIT times connection failure.


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.


If enabled any hosts which have been flagged as disabled will be removed from the list of servers in the memcached_st structure.

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.

When enabled the prefix key will be added to the key when determining server by hash. See MEMCACHED_CALLBACK_NAMESPACE for additional information.



Distribute keys by hash modulo number of servers.

Alias for MEMCACHED_DISTRIBUTION_CONSISTENT_KETAMA.

Unweighted consistent key distribution.

Distribute keys by rand(3) modulo number of servers.

Unweighted consistent key distribution compatible with the SPY client.

Weighted consistent key distribution.

Consistent key distribution by virtual buckets.


DESCRIPTION

libmemcached 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 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.

RETURN VALUE

memcached_behavior_get() returns either the current value of the key, or 0 or 1 on simple flag behaviors (1 being enabled). memcached_behavior_set() returns failure or success.

NOTES

The data argument of memcached_behavior_set() was changed in version 0.17 from taking a pointer to data value, to taking a uin64_t.

SEE ALSO

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

November 12, 2021 1.1