[BUG] The configuration item rocksdb.compression cannot take effect

[caipengbo]

Kvrocks has a configuration item called rocksdb.compression, which is assigned to rocksdb::Options:
https://github.com/KvrocksLabs/kvrocks/blob/2e43741ddedc06f0376d71dc385e9d53a24b3204/src/storage.cc#L87

But Kvrocks calls rocksdb's built-in optimization function:
https://github.com/KvrocksLabs/kvrocks/blob/2e43741ddedc06f0376d71dc385e9d53a24b3204/src/storage.cc#L80

This function will set compression_per_level. Like the Rocksdb Wiki says, when options.compression_per_level is used, options.compression is ignored.

Rocksdb's built-in optimization function selects the best compression algorithm. So do we need to remove rocksdb.compression configuration item in Kvrocks?

[git-hulk]

Good catch, as OptimizeLevelStyleCompaction would use the lz4 first then the snappy if supported, but they're still some other compressions. So seems that we can NOT enable the OptimizeLevelStyleCompaction when the compression was explicitly specified, HDYT.

[caipengbo]

OptimizeLevelStyleCompaction function also optimizes other parameters, such as write_buffer_size , max_bytes_for_level_base , and so on. But we'll overwrite these parameters later.

Maybe can we get rid of OptimizeLevelStyleCompaction, then set compression_per_level in kvrocks?

[git-hulk]

Looks fine for me