Compression¶
Transparent compression is to reduce the use of memory and network bandwidth by big keys and improve request performance.
Protocol Design¶
Mark the data to be compressed by adding a header before the compressed data, the following diagram depicts the protocol:
+
|
header compressed data
|
1byte |
+------+-------+-------+-------+--------+----------------------------------+
| | | | | | | ...
+--+---+-------+--+----+---+---+----+---+--+-------------------------------+
| | | | | |
| | algorithm +--+---+ |
+-------+------+ + |
+ \r\n |
magic number |
|
+
Examle(snappy)¶
- Before
echo -n $(redis-cli -h ${BACKEND_HOST} GET TEST_KEY) | xxd
00000000: 3030 3030 3030 3030 3030 3030 3030 3030 0000000000000000
00000010: 3030 3030 3030 3030 3030 3030 3030 3030 0000000000000000
00000020: 3030 3030 3030 3030 3030 3030 3030 3030 0000000000000000
00000030: 3030 3030 3030 3030 3030 3030 3030 3030 0000000000000000
00000040: 3030 3030 3030 3030 3030 3030 3030 3030 0000000000000000
00000050: 3030 3030 3030 3030 3030 3030 3030 00000000000000
- After
echo -n $(redis-cli -h ${BACKEND_HOST} GET TEST_KEY) | xxd
00000000: 2850 2400 0d0a ff06 0000 734e 6150 7059 (P$.......sNaPpY
00000010: 000d 0000 faca b4a7 5e00 30fe 0100 7201 ........^.0...r.
00000020: 00 .
Prameters¶
Compatibility¶
Now support Strings and Hashes.
When compression is enabled, commands such as GETBIT are disabled.
Other commands are not processed and passed directly to the backend.
Warning
Using GETBIT on the compressed value after the compressed mode
is closed will return unexpected results.
| COMMAND | Support |
|---|---|
| SET | Y |
| MSET | Y |
| GETSET | Y |
| SETNX | Y |
| HSET | Y |
| HMSET | Y |
| PSETEX | Y |
| SETEX | Y |
| HSETEX | Y |
| APPEND | N |
| EVAL | N |
| SETBIT | N |
| SETRANGE | N |
| GETBIT | N |
| GETRANGE | N |
Compress Algorithm¶
Note
The algorithm in the header is a byte not a string.
-
0: snappy
-
255: mock, only for unit test
Performance¶
TBD