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|
## Memcache Command Support
### Request
- Twemproxy implements only the memached ASCII commands
- Binary commands are currently unsupported
#### Ascii Storage Command
+-------------------+------------+--------------------------------------------------------------------------+
| Command | Supported? | Format |
+-------------------+------------+--------------------------------------------------------------------------+
| set | Yes | set <key> <flags> <expiry> <datalen> [noreply]\r\n<data>\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| add | Yes | add <key> <flags> <expiry> <datalen> [noreply]\r\n<data>\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| replace | Yes | replace <key> <flags> <expiry> <datalen> [noreply]\r\n<data>\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| append | Yes | append <key> <flags> <expiry> <datalen> [noreply]\r\n<data>\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| prepend | Yes | prepend <key> <flags> <expiry> <datalen> [noreply]\r\n<data>\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| cas | Yes | 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
#### Ascii Retrieval Command
+-------------------+------------+--------------------------------------------------------------------------+
| Command | Supported? | Format |
+-------------------+------------+--------------------------------------------------------------------------+
| get | Yes | get <key> [<key>]+\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| gets | Yes | gets <key> [<key>]+\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
#### Ascii Delete
+-------------------+------------+--------------------------------------------------------------------------+
| Command | Supported? | Format |
+-------------------+------------+--------------------------------------------------------------------------+
| delete | Yes | delete <key> [noreply]\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
#### Ascii Arithmetic Command
+-------------------+------------+--------------------------------------------------------------------------+
| Command | Supported? | Format |
+-------------------+------------+--------------------------------------------------------------------------+
| incr | Yes | incr <key> <value> [noreply]\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| decr | Yes | decr <key> <value> [noreply]\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
* Where,
* <value> - uint64_t
#### Ascii Misc Command
+-------------------+------------+--------------------------------------------------------------------------+
| Command | Supported? | Format |
+-------------------+------------+--------------------------------------------------------------------------+
| touch | Yes | touch <key> <expiry>[noreply]\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| gat | Planned | gat <expiry> <key>+\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| gats | Planned | gats <expiry> <key>+\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| quit | Yes | quit\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| flush_all | No | flush_all [<delay>] [noreply]\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| version | Yes | version\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| verbosity | No | verbosity <num> [noreply]\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| stats | No | stats\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
| stats | No | stats <args>\r\n |
+-------------------+------------+--------------------------------------------------------------------------+
### Response
#### 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 Responses
NOT_FOUND\r\n
DELETED\r\n
#### Retrieval 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
#### Touch Command Responses
NOT_FOUND\r\n
TOUCHED\r\n
#### Statistics Response
[STAT <name> <value>\r\n]+END\r\n
#### Misc Responses
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
https://stackoverflow.com/questions/2525188/are-binary-protocols-dead
- nutcracker will support the more efficient meta-text protocol after the protocol
is marked as stable and memcached servers using it have had several releases.
- https://news.ycombinator.com/item?id=1712788
|
