refactor(storage): create new read snapshot to read for StateStore trait

[wenym1]

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What's changed and what's your intention?

Previously we have two traits to read in storage, LocalStateStore and StateStoreRead. One difference in the two traits is that, for StateStoreRead, we have to specify the epoch to read on, while for LocalStateStore, since its read methods always read from the latest snapshot, we don't need to specify the epoch.

In #20153, we introduce a new associated type FlushedSnapshotReader, which also reads data from the latest snapshot. However, since it implements the StateStoreRead trait, when we call its read methods, we still need to specify the epoch, which is actually unnecessary. Besides, it will be cleaner if we are able to make the read methods more unified in the trait definition.

Therefore, in this PR, we will remove the epoch parameter from the read methods of StateStoreRead trait. Instead, we add a new method new_read_snapshot to StateStore, whose return type is a new associated type ReadSnapshot that implements StateStoreRead. In the new_read_snapshot method, we specify the epoch and table_id to read. In the implementation of HummockStorage on new_read_snapshot, we also do try_wait_epoch on the epoch, so that the returned ReadSnapshot is ready to read.

Changes in the trait definition is as followed:

pub trait StateStoreRead: StaticSendSync {
    fn get(
        &self,
        key: TableKey<Bytes>,
        //  epoch: u64, // epoch is removed
        ...

    fn iter(
        &self,
        key_range: TableKeyRange,
        //  epoch: u64, // epoch is removed
        ...

    fn rev_iter(
        &self,
        key_range: TableKeyRange,
        //  epoch: u64, // epoch is removed
        ...
}

pub trait StateStore: StateStoreReadLog + StaticSendSync + Clone {
    type ReadSnapshot: StateStoreRead + Clone;

    fn new_read_snapshot(
        &self,
        epoch: HummockReadEpoch,
        options: NewReadSnapshotOptions,
    ) -> impl StorageFuture<'_, Self::ReadSnapshot>;
    ...
}

Checklist

• I have written necessary rustdoc comments.
• I have added necessary unit tests and integration tests.
• I have added test labels as necessary.
• I have added fuzzing tests or opened an issue to track them.
• My PR contains breaking changes.
• My PR changes performance-critical code, so I will run (micro) benchmarks and present the results.
• My PR contains critical fixes that are necessary to be merged into the latest release.

Documentation

• My PR needs documentation updates.

Release note

[wenym1]

• refactor(storage): unify state store trait get method #20175
• refactor(storage): create new read snapshot to read for StateStore trait #20172 👈 (View in Graphite)
• feat(storage): refactor and support local state store flushed snapshot reader #20153
• main

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