tikv raftstore-v2: implement local read for raftstore-v2

What is changed and how it works?

Issue Number: Ref #12842

What's Changed:

This PR involves:

Refactor LocalReader of raftstore-v1 to make some code sharable with raftstore-v2
Implement LocalReader of raftstore-v2 and add relevant tests
Replace callback with ReadCallback trait

Related changes

PR to update pingcap/docs/pingcap/docs-cn:
Need to cherry-pick to the release branch

Check List

Tests

Unit test
Integration test

Release note

None

Aug 30 '22 03:08 SpadeA-Tang

[REVIEW NOTIFICATION]

This pull request has been approved by:

5kbpers
tonyxuqqi

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Aug 30 '22 03:08 ti-chi-bot

/test

Sep 21 '22 10:09 SpadeA-Tang

/test

Oct 08 '22 15:10 SpadeA-Tang

/merge

Oct 11 '22 08:10 5kbpers

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Oct 11 '22 08:10 ti-chi-bot

This pull request has been accepted and is ready to merge.

Commit hash: 0ee256b7e5afe2fe03bf67e949ffb4b0842b0c20

Oct 11 '22 08:10 ti-chi-bot

/test

Oct 11 '22 08:10 SpadeA-Tang

Why merge this? I think it depends on #13568

Oct 11 '22 10:10 BusyJay

Why merge this? I think it depends on #13568

The circumstance here is much easier. It only has snap oepration and does not have cache.

Oct 11 '22 10:10 SpadeA-Tang

The circumstance here is much easier. It only has snap oepration and does not have cache.

It doesn't have cross snapshot cache, but it may has cache within the same region. And this PR also lacks the check of last_valid_ts.

Oct 11 '22 10:10 BusyJay

The circumstance here is much easier. It only has snap oepration and does not have cache.

It doesn't have cross snapshot cache, but it may has cache within the same region. And this PR also lacks the check of last_valid_ts.

Checking last_valid_ts means we have to acquire the system time twice? One before getting the snapshot and one after it.

Oct 11 '22 10:10 SpadeA-Tang

Checking last_valid_ts means we have to acquire the system time twice? One before getting the snapshot and one after it.

Yes, for V1. For v2, only check if latest tablet is None is sufficient.

Oct 11 '22 10:10 BusyJay