Write-Through Inter-Block Cache

[alexanderbez]

• Restructure baseapp/ directory by logical grouping to improve readability.
• Improve BaseApp docs w/ diagrams 🎉
• Implement CommitKVStoreCacheManager which acts as a persistent inter-block write-through cache.
  • It contains a mapping from StoreKey to a *CommitKVStoreCache (LRU ARC cache).
  • A single instance of CommitKVStoreCacheManager is created in an app and set on the BaseApp.
  • The BaseApp sets this persistent cache on the root CommitMultiStore.
  • When the version is loaded, each IAVL Store is wrapped with it's own respective *CommitKVStoreCache.
  • Writes happen in a write-through fashion.

Preliminary benchmarks show there is only a marginal improvement.

closes: #1947

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• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry: clog add [section] [stanza] [message]

• rereviewed Files changed in the github PR explorer

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[tnachen]

Is this related to the cahce change?

[alexanderbez]

Not directly, but was needed for initial benchmarking which I henceforth removed. So technically I can undo this change, but we only support secp256k1 keys anyway. Might as well keep it.

[fedekunze]

utACK

[alexanderbez]

@cwgoes I've shared benchmarks and we can see this does indeed offer great improvement, specifically within BeginBlock.

I've addressed all comments @AdityaSripal @tnachen 👍

[cwgoes]

utACK on the inter-block cache implementation; I didn't review the baseapp changes.