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memcache.txt
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memcache.txt
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- ascii:
- Storage Commands (set, add, replace, append, prepend, cas):
set <key> <flags> <expiry> <datalen> [noreply]\r\n<data>\r\n
add <key> <flags> <expiry> <datalen> [noreply]\r\n<data>\r\n
replace <key> <flags> <expiry> <datalen> [noreply]\r\n<data>\r\n
append <key> <flags> <expiry> <datalen> [noreply]\r\n<data>\r\n
prepend <key> <flags> <expiry> <datalen> [noreply]\r\n<data>\r\n
cas <key> <flags> <expiry> <datalen> <cas> [noreply]\r\n<data>\r\n
where,
<flags> - uint32_t : data specific client side flags
<expiry> - uint32_t : expiration time (in seconds)
<datalen> - uint32_t : size of the data (in bytes)
<data> - uint8_t[]: data block
<cas> - uint64_t
- Retrival Commands (get, gets):
get <key>\r\n
get <key> [<key>]+\r\n
gets <key>\r\n
gets <key> [<key>]+\r\n
- Delete Command (delete):
delete <key> [noreply]\r\n
- Arithmetic Commands (incr, decr):
incr <key> <value> [noreply]\r\n
decr <key> <value> [noreply]\r\n
where,
<value> - uint64_t
- Misc Commands (quit)
quit\r\n
flush_all [<delay>] [noreply]\r\n
version\r\n
verbosity <num> [noreply]\r\n
- Statistics Commands
stats\r\n
stats <args>\r\n
- Error Responses:
ERROR\r\n
CLIENT_ERROR [error]\r\n
SERVER_ERROR [error]\r\n
where,
ERROR means client sent a non-existent command name
CLIENT_ERROR means that command sent by the client does not conform to the protocol
SERVER_ERROR means that there was an error on the server side that made processing of the command impossible
- Storage Command Responses:
STORED\r\n
NOT_STORED\r\n
EXISTS\r\n
NOT_FOUND\r\n
where,
STORED indicates success.
NOT_STORED indicates the data was not stored because condition for an add or replace wasn't met.
EXISTS indicates that the item you are trying to store with a cas has been modified since you last fetched it.
NOT_FOUND indicates that the item you are trying to store with a cas does not exist.
- Delete Command Response:
NOT_FOUND\r\n
DELETED\r\n
- Retrival Responses:
END\r\n
VALUE <key> <flags> <datalen> [<cas>]\r\n<data>\r\nEND\r\n
VALUE <key> <flags> <datalen> [<cas>]\r\n<data>\r\n[VALUE <key> <flags> <datalen> [<cas>]\r\n<data>]+\r\nEND\r\n
- Arithmetic Responses:
NOT_FOUND\r\n
<value>\r\n
where,
<value> - uint64_t : new key value after incr or decr operation
- Statistics Response
[STAT <name> <value>\r\n]+END\r\n
- Misc Response
OK\r\n
VERSION <version>\r\n
- Notes:
- set always creates mapping irrespective of whether it is present on not.
- add, adds only if the mapping is not present
- replace, only replaces if the mapping is present
- append and prepend command ignore flags and expiry values
- noreply instructs the server to not send the reply even if there is an error.
- decr of 0 is 0, while incr of UINT64_MAX is 0
- maximum length of the key is 250 characters
- expiry of 0 means that item never expires, though it could be evicted from the cache
- non-zero expiry is either unix time (# seconds since 01/01/1970) or,
offset in seconds from the current time (< 60 x 60 x 24 x 30 seconds = 30 days)
- expiry time is with respect to the server (not client)
- <datalen> can be zero and when it is, the <data> block is empty.
- Thoughts:
- ascii protocol is easier to debug - think using strace or tcpdump to see
protocol on the wire, Or using telnet or netcat or socat to build memcache
requests and responses
http://stackoverflow.com/questions/2525188/are-binary-protocols-dead
- http://news.ycombinator.com/item?id=1712788