6. refactor(state): prepare finalized state for shared read-only access

[teor2345]

Motivation

As part of #3745, we need to be able to clone read-only access to the finalized state.

Designs

The DiskDb type provides shared read-write access to the low-level types in the finalized state. (Like individual column family entries.)

That's enough for initial performance testing, but later PRs will allow shared access to high-level types. (Like composite types and queries.)

Write access requires a lot of manual low-level code, so it should be obvious in reviews. The high-level type wrapper might also prevent write access, but that's not a priority.

Solution

• wrap the underlying RocksDB instance in an Arc
• only shut down the database when the last shared instance is dropped
• implement Eq

Review

This is a bit urgent, because it blocks most of the lightwalletd integration tests.

Reviewer Checklist

• Code implements Specs and Designs
• Tests for Expected Behaviour
• Tests for Errors

Follow Up Work

• Zebra takes too much time to respond to getblock RPC method. #3745

[teor2345]

@Mergifyio update

[mergify]

update

☑️ Nothing to do

• -closed [:pushpin: update requirement]
• #commits-behind>0 [:pushpin: update requirement]

[codecov]

Codecov Report

Merging #3810 (d8a79b6) into split-state-service (984e0b1) will decrease coverage by 0.03%.
The diff coverage is 59.64%.

@@                   Coverage Diff                   @@
##           split-state-service    #3810      +/-   ##
=======================================================
- Coverage                78.86%   78.82%   -0.04%     
=======================================================
  Files                      293      293              
  Lines                    33560    33603      +43     
=======================================================
+ Hits                     26466    26487      +21     
- Misses                    7094     7116      +22     

[conradoplg]

Looks good, just have a question. Feel free to mark it as solved if there is no issue there.

[teor2345]

Fetching the Zcash parameters caused the Windows test to time out.