The module provides:

• Zstandard compression
• Optional transparent mode for Strings where SET/GET commands are translated to the equivalant compress / decompress command (Example).
• Ability to train Zstandard dictionaries on data stored in Redis (Example).
• Prefix-specific dictionary support: different keys can use different dictionaries to maximize compression efficiency (Example).

$ redis-server --loadmodule librediscompress.so
$ cat blob | redis-cli -x compress.set foo
$ redis-cli compress.get foo

Check effectivness of compression

$ redis-cli info modules
...
# Modules
module:name=compress,ver=1,api=1,filters=0,usedby=[],using=[],options=[]

# compress_stats
compress_zstd_version:10405
compress_compression_ratio:7.70
compress_compressed_size:210842569
compress_uncompressed_size:1623962898
compress_objects:100000
compress_dictionaries:23

$ redis-cli compress.transparent on
$ cat blob | redis-cli -x set foo
$ redis-cli type foo
ZipStr001
$ redis-cli get foo

WARNING: Traning a dictionary leaks memory (~6 MB per operation). It's recommended that all TRAIN operations are performed on a replica.

A default dictionary will be used for any key that doesn't have prefix that matches a prefix-specific dictionary []. To train a new default dictionary:

$ redis-cli compress.dict train
1) (integer) 1600643999514
2) (integer) 21748
3) (integer) 397

In the above example, the dictionary has ID 1600643999514 and is 21748 bytes. It was trained on 397 objects. The default target size for dictionaries is 100 KB, but can be changed using the DICTSIZE option.

To train a new dictionary for keys that match a specific prefix, use the PREFIX option:

$ redis-cli compress.dict train prefix foo

You can use the COMPRESS.DICT LIST command to get details about loaded dictionaries.

Compresses value and stores it in key. If a key already holds a value, it's overwritten and TTL is discarded. If data cannot be compressed, then key is turned into a normal (uncompressed) string.

NOTE COMPRESS.SET does not currently support the standard SET options.

Simple string, or Null reply. Same as the standard SET command.

Returns the decompressed version of key.

Bulk string. Value of key, or nil when the key does not exists.

Toggle transparent compression mode. When transparent mode is ON:

• SET operations are transformed to COMPRESS.SET.
• GET operations are transformed to COMPRESS.GET

Integer reply: number of command filters enabled or disabled.

redis> COMPRESS.TRANSPARENT on
2

Train a new dictionary using data stored in Redis.

WARNING Training a dictionary leaks about 6 MB of memory and the operation runs synchronously and can therefor block other operations for a significant period of time. It is strongly recommended that all TRAIN operations are preformed on a replica.

An array with the following items:

• Dictionary ID
• Dictionary size in bytes
• Number of objects used to trains the dictionary

Removes the dictionary so that no new objects can be compressed using it. However, the dictionary will only be removed from Redis once all objects already compressed using the dictionary are removed.

Simple string.

Dumps the content of a dictionary so that it can later be loaded using COMPRESS.DICT RESTORE.

Bulk string.

$ redis-cli compress.dict dump 1600643999514 > dict.raw
$ cat dict.raw | redis-cli -x compress.dict restore

Creates a new dictionary from the provided dictionary data. The data could have been obtained using COMPRESS.DICT DUMP or through any zstd --train.

NOTE Currently only supported for the default dictionary.

Simple string.

List available dictionaries.

An array of arrays, where each sub-array represents a dictionary. Each dictionary has the following:

• Dictionary ID
• Prefix (or "" if none)
• Number of objects currently compressed using the dictionary
• Uncompressed size of all objects using the dictionary
• Compressed size of all objects using the dictionary
• Compression ratio

redis> COMPRESS.DICT LIST
1) 1) (integer) 1600644598087
   2) "foo"
   3) (integer) 398
   4) (integer) 39437
   5) (integer) 17635
   6) "2.2362914658349871"
2) 1) (integer) 1600644598117
   2) "bar"
   3) (integer) 72
   4) (integer) 28946
   5) (integer) 22003
   6) "1.3155478798345681"