Memcached Commands

Memcached supports the TCP-based text protocol and binary protocol. Any clients compatible with a Memcached protocol can access DCS instances.

Memcached Text Protocol

The Memcached text protocol uses ASCII text to transfer commands, which helps you compile clients and debug problems. DCS Memcached instances can even be directly connected using Telnet.

Compared with the Memcached binary protocol, the Memcached text protocol is compatible with more open-source clients, but the text protocol does not support authentication.

Clients can use the Memcached text protocol to access DCS Memcached instances only if password-free access is enabled. Password-free access means that access to DCS Memcached instances will not be username- and password-protected, and any Memcached clients that satisfy security group rules in the same VPC can access the instances. Enabling password-free access poses security risks. Exercise caution when enabling password-free access.

Table 1 lists the commands supported by the Memcached text protocol and describes whether these commands are supported by DCS Memcached instances.

**Table 1** Commands supported by the Memcached text protocol
Command	Function	Supported by DCS
add	Adding data	Yes
set	Sets data, including adding or modifying data.	Yes
replace	Replaces data.	Yes
append	Adds data after the value of the specified key.	Yes
prepend	Adds data before the value of a specified key.	Yes
cas	Checks and set data.	Yes
get	Queries data.	Yes
gets	Queries data details.	Yes
delete	Deletes data.	Yes
incr	Adds the specified amount to the requested counter.	Yes
decr	Removes the specified amount to the requested counter.	Yes
touch	Updates the expiration time of existing data.	Yes
quit	Closes the connection.	Yes
flush_all	Clearing DCS instance data NOTE: The value of the delay option (if any) must be 0.	Yes
version	Queries Memcached version information.	Yes
stats	Manages operation statistics. NOTE: Currently, only basic statistics can be queried. Commands on optional parameters cannot be queried.	Yes
cache_memlimit	Adjusts the cache memory limit.	No
slabs	Queries usage of internal storage structures.	No
lru	Manages policies of deleting expired data.	No
lru_crawler	Manages threads of deleting expired data.	No
verbosity	Sets the verbosity level of the logging output.	No
watch	Inspects what's going on internally.	No

Memcached Binary Protocol

The Memcached binary protocol encodes commands and operations into specific structures before sending them. Commands are represented by predefined character strings.

The Memcached binary protocol provides more features but fewer clients than the Memcached text protocol. The Memcached binary protocol is more secure than the Memcached text protocol as it additionally supports simple authentication and security layer (SASL) authentication.

Table 2 lists the commands supported by the Memcached binary protocol and describes whether these commands are supported by DCS Memcached instances.

**Table 2** Commands supported by the Memcached binary protocol
Command Code	Command	Function	Supported by DCS
0x00	GET	Queries data.	Yes
0x01	SET	Sets data, including adding or modifying data.	Yes
0x02	ADD	Adding data	Yes
0x03	REPLACE	Replaces data.	Yes
0x04	DELETE	Deletes data.	Yes
0x05	INCREMENT	Adds the specified amount to the requested counter.	Yes
0x06	DECREMENT	Removes the specified amount to the requested counter.	Yes
0x07	QUIT	Closes the connection.	Yes
0x08	FLUSH	Clearing DCS instance data NOTE: The value of the delay option (if any) must be 0.	Yes
0x09	GETQ	Queries data. The client will not receive any response in case of failure.	Yes
0x0a	NOOP	No-operation instruction, equivalent to ping.	Yes
0x0b	VERSION	Queries Memcached version information.	Yes
0x0c	GETK	Queries data and adds a key into the response packet.	Yes
0x0d	GETKQ	Queries data and returns a key. The client will not receive any response in case of failure.	Yes
0x0e	APPEND	Adds data after the value of the specified key.	Yes
0x0f	PREPEND	Adds data before the value of a specified key.	Yes
0x10	STAT	Queries statistics of DCS Memcached instances. NOTE: Currently, only basic statistics can be queried. Commands on optional parameters cannot be queried.	Yes
0x11	SETQ	Sets data, including adding or modifying data. The SETQ command only returns a response on failures. The client will not receive any response in the case of success.	Yes
0x12	ADDQ	Adds data. The client will not receive any response in the case of success.	Yes
0x13	REPLACEQ	Replaces data. The client will not receive any response in the case of success.	Yes
0x14	DELETEQ	Deletes data. The client will not receive any response in the case of success.	Yes
0x15	INCREMENTQ	Adds the specified amount to the requested counter. The client will not receive any response in the case of success.	Yes
0x16	DECREMENTQ	Removes the specified amount to the requested counter. The client will not receive any response in the case of success.	Yes
0x17	QUITQ	Closes the connection.	Yes
0x18	FLUSHQ	Clears data and returns no information. NOTE: The value of the delay option (if any) must be 0.	Yes
0x19	APPENDQ	Adds data after the value of the specified key. The client will not receive any response in the case of success.	Yes
0x1a	PREPENDQ	Adds data before the value of a specified key. The client will not receive any response in the case of success.	Yes
0x1c	TOUCH	Updates the expiration time of existing data.	Yes
0x1d	GAT	Queries data and updates the expiration time of existing data.	Yes
0x1e	GATQ	Queries data and returns a key. The client will not receive any response in case of failure.	Yes
0x23	GATK	Queries data, adds a key into the response packet, and updates the expiration time of existing data.	Yes
0x24	GATKQ	Queries data, returns a key, and updates the expiration time of existing data. The client will not receive any response in case of failure.	Yes
0x20	SASL_LIST_MECHS	Asks the server what SASL authentication mechanisms it supports.	Yes
0x21	SASL_AUTH	Starts SASL authentication.	Yes
0x22	SASL_STEP	Further authentication steps are required.	Yes