High memory usage with paritydb

[liuchengxu]

It's observed that simply running subcoin with paritydb for the initial Bitcoin full sync could consume up to 50+GB memory when the chain syncs ~400000 blocks on my machine (128 GB in total, Ubuntu 22.04), which is ridiculous. Rocksdb does not have this issue, the peek memory usage of rocksdb is less than 2GB when the chain syncs to the same height. It's a known issue of paritydb (paritytech/parity-db#168) We should find a workaround or disable paritydb and stick with rocksdb before the memory issue is resolved upstream.

[liuchengxu]

Based on a recent test conducted on a cloud machine with 8 GiB of memory, there doesn't appear to be any issue. The memory usage for Subcoin remained stable at around 35%, and there were no fatal errors such as OOM. It seems that ParityDB only uses a proportion of the available memory, and the usage does not increase indefinitely. Therefore, running with ParityDB should not pose a problem.