Storage query performance optimization

[ntduan]

fix #332

[shunjizhan]

question: why don't we cache blockHash => Storage, and instead cache registry => Storage? It seems that we are repeating this deterministic query (is this line actually not deterministic?)

const registry = await this.api.getBlockRegistry(u8aToU8a(blockHash));

Also, do we have a limit for the cache? It can grow very big in long term

[ntduan]

question: why don't we cache blockHash => Storage, and instead cache registry => Storage? It seems that we are repeating this deterministic query (is this line actually not deterministic?)

const registry = await this.api.getBlockRegistry(u8aToU8a(blockHash));

Also, do we have a limit for the cache? It can grow very big in long term

Because the registry only changes when the chain version is upgraded. This will not be very frequent.

apiAt creates a new object every time, which can cause a significant performance overhead. https://github.com/polkadot-js/api/blob/master/packages/api/src/base/Init.ts#L120