replica_rac2: add admitted state protocol

[pav-kv]

This PR introduces AdmittedState and PiggybackedAdmittedState protos, and converts replica- and leader-side code (such as AdmittedPiggybacker and raft transport) to use them.

The protos are not populated at the moment, and the leader-side code is a bunch of TODOs. More conversion code will follow, to replace the AdmittedResponseForRange flows.

Part of #129508

[cockroach-teamcity]

This change is 

[sumeerbhola]

Reviewed 2 of 2 files at r1, 1 of 1 files at r2, 10 of 10 files at r3, 2 of 2 files at r4, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @pav-kv)

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pkg/kv/kvserver/raft_transport.go line 753 at r3 (raw file):

		// TODO(pav-kv): send these protos once they are populated correctly.
		if true {
			return

Any reason not to do this now, so it can be tested? I suppose TestFlowControlRaftTransportV2 did not test whether the outgoing message actually included the piggybacked state. Worth leaving a TODO in that test.

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pkg/kv/kvserver/raft_transport.go line 770 at r3 (raw file):

		batch.Requests = batch.Requests[:0]
		batch.StoreIDs = nil
		batch.Now = hlc.ClockTimestamp{}

this needs to clear the AdmittedStates slice too.

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pkg/kv/kvserver/raft_transport.go line 810 at r3 (raw file):

			var pendingDispatches []kvflowcontrolpb.AdmittedRaftLogEntries
			var admittedStates []kvflowcontrolpb.PiggybackedAdmittedState

nit: do we need this declared here, or can it be declared at usage time below.

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pkg/kv/kvserver/raft_transport.go line 831 at r3 (raw file):

					kvadmission.FlowTokenDispatchMaxBytes.Get(&t.st.SV),
				)
				maybeAnnotateWithAdmittedRaftLogEntries(req, pendingDispatches)

if we want to reuse this test knob for v2, we should do the annotation here. We have the batch.

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pkg/kv/kvserver/kvflowcontrol/node_rac2/admitted_piggybacker_test.go line 44 at r3 (raw file):

				d.ScanArgs(t, "store-id", &storeID)
				d.ScanArgs(t, "range-id", &rangeID)
				d.ScanArgs(t, "term", &term)

can you add the replicaID fields too.

[pav-kv]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @sumeerbhola)

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pkg/kv/kvserver/raft_transport.go line 753 at r3 (raw file):

Previously, sumeerbhola wrote…

Any reason not to do this now, so it can be tested? I suppose TestFlowControlRaftTransportV2 did not test whether the outgoing message actually included the piggybacked state. Worth leaving a TODO in that test.

Added a TODO. Choosing not to send these messages just yet to be sure that none of this is on the wire in master/prod right now. Just in case we want to tweak these protos while developing (similarly to how we changed the proto definition in this PR in a backwards-incompatible way because we're sure these protos aren't populated yet). I want to enable the send when the replica integration is done and the leader can handle these updates, and both parts are covered by tests.

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pkg/kv/kvserver/raft_transport.go line 770 at r3 (raw file):

Previously, sumeerbhola wrote…

this needs to clear the AdmittedStates slice too.

Done.

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pkg/kv/kvserver/raft_transport.go line 810 at r3 (raw file):

Previously, sumeerbhola wrote…

nit: do we need this declared here, or can it be declared at usage time below.

Could be done, but after moving the annotation to the knob branch below (per other comment), the slice has to be defined in this line.

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pkg/kv/kvserver/raft_transport.go line 831 at r3 (raw file):

Previously, sumeerbhola wrote…

if we want to reuse this test knob for v2, we should do the annotation here. We have the batch.

Done.

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pkg/kv/kvserver/kvflowcontrol/node_rac2/admitted_piggybacker_test.go line 44 at r3 (raw file):

Previously, sumeerbhola wrote…

can you add the replicaID fields too.

Done.

[sumeerbhola]

Reviewed 9 of 10 files at r6, 2 of 2 files at r7, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @pav-kv)

[pav-kv]

TFTR!

bors r=sumeerbhola

[craig]

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