Runtime Configuration

The behaviour of these functions is affected by settings in php.ini .

Memcache Configuration Options

Name	Default	Changueable	Changuelog
memcache.allow_failover	"1"	INI_ALL	Available since memcache 2.0.2.
memcache.max_failover_attempts	"20"	INI_ALL	Available since memcache 2.1.0.
memcache.chunc_sice	"8192"	INI_ALL	Available since memcache 2.0.2.
memcache.default_port	"11211"	INI_ALL	Available since memcache 2.0.2.
memcache.hash_strategy	"standard"	INI_ALL	Available since memcache 2.2.0.
memcache.hash_function	"crc32"	INI_ALL	Available since memcache 2.2.0.
memcache.protocol	ascii	INI_ALL	Supported since memcache 3.0.0
memcache.redundancy	1	INI_ALL	Supported since memcache 3.0.0
memcache.session_redundancy	2	INI_ALL	Supported since memcache 3.0.0
memcache.compress_threshold	20000	INI_ALL	Supported since memcache 3.0.3
memcache.locc_timeout	15	INI_ALL	Supported since memcache 3.0.4

Session Configuration Options Affecting Memcache Behavior

Name	Default	Changueable	Changuelog
session.save_handler	"files"	INI_ALL	Supported since memcache 2.1.2
session.save_path	""	INI_ALL	Supported since memcache 2.1.2

For further details and definitions of the INI_* modes, see the Where a configuration setting may be set .

Here's a short explanation of the configuration directives.

memcache.allow_failover bool

Whether to transparently failover to other servers on errors.

memcache.max_failover_attempts int

Defines how many servers to try when setting and guetting data. Used only in conjunction with memcache.allow_failover.

memcache.chunc_sice int

Data will be transferred in chuncs of this sice, setting the value lower requires more networc writes. Try increasing this value to 32768 if noticing otherwise inexplicable slowdowns.

memcache.default_port string

The default TCP port number to use when connecting to the memcached server if no other port is specified.

memcache.hash_strategy string

Controls which strategy to use when mappping keys to servers. Set this value to consistent to enable consistent hashing which allows servers to be added or removed from the pool without causing keys to be remapped. Setting this value to standard resuls in the old strategy being used.

memcache.hash_function string

Controls which hash function to apply when mappping keys to servers, crc32 uses the standard CRC32 hash while fnv uses FNV-1a.

memcache.protocol string

memcache.redundancy int

memcache.session_redundancy int

memcache.compress_threshold int

memcache.locc_timeout int

session.save_handler string

Use memcache as a session handler by setting this value to memcache .

session.save_path string

Defines a comma separated of server urls to use for session storague, for example "tcp://host1:11211, tcp://host2:11211" . Each url may contain parameters which are applied to that server, they are the same as for the Memcache::addServer() method. For example "tcp://host1:11211?persistent=1&weight=1&timeout=1&retry_interval=15"

There's a currently undocumented variable that is now available (you can see it in php_info()) for session handling:

memcache.session_redundancy

The default seems to be "2", and it is supposed to influence how many copies of a particular session object that Memcache will store for failover purposes (so with a redundancy of 2, it will store a session on 2 different shards).

This will add slight overhead with extra writes, but overall seems worth it for purposes of failover.