Merge #32954

32954: storage: add interfaces for copysets r=tbg a=mvijaykarthik

Copysets significantly reduce the probability of data loss
in the presence of multi node failures. The RFC for copysets
is presented in https://github.com/cockroachdb/cockroach/pull/32816.

This commit adds interfaces and protos for copysets.
The implementation added later will have two independent tracks:
1. Assignment and persistance of store_id-copyset_id mapping.
2. Rebalancer changes to rebalance replicas into copysets.

Release note: None
Co-authored-by: Vijay Karthik <[email protected]>

pkg/storage/copysets/copysets.go

+// Copyright 2019 The Cockroach Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied. See the License for the specific language governing
+// permissions and limitations under the License.
+
+package copysets
+
+import "context"
+
+// CopysetID is a custom type for a cockroach copyset ID.
+// Copyset is a group of stores where a range should be contained within
+// if copyset based rebalancing is enabled.
+type CopysetID int32
+
+// Reader is used to read copysets in the cluster.
+type Reader interface {
+	// forRF returns copysets for the given replication factor.
+	forRF(ctx context.Context, replicationFactor int32) (*Copysets, error)
+}
+
+// Maintainer maintains and assigns copysets to stores.
+// TODO(hassan): implement Maintainer.
+type Maintainer struct {
+}
+
+// Ensure Maintainer implements Reader.
+var _ Reader = &Maintainer{}
+
+// forRF returns copysets for the given replication factor.
+func (cs *Maintainer) forRF(ctx context.Context, replicationFactor int32) (*Copysets, error) {
+	return nil, nil
+}

pkg/storage/copysets/copysets.proto

+// Copyright 2019 The Cockroach Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied. See the License for the specific language governing
+// permissions and limitations under the License.
+
+syntax = "proto3";
+package cockroach.storage.copysets;
+option go_package = "copysets";
+
+import "gogoproto/gogo.proto";
+
+// CopysetStrategy has the set of supported copyset-store allocation strategies.
+enum CopysetStrategy {
+  // MAXIMIZE_DIVERSITY is a strategy which tries to maximize locality diversity
+  // when creating copysets from a store list.
+  MAXIMIZE_DIVERSITY = 0;
+  // MINIMIZE_MOVEMENT is a strategy which tries to minimize changes to
+  // existing copysets when generating new copysets on store list changes.
+  // It does not guarantee optimal locality diversity but tries to avoid
+  // stores with same localities within copysets.
+  MINIMIZE_MOVEMENT = 1;
+}
+
+// AllCopysets contains the map between replication factor to
+// its copysets.
+message AllCopysets {
+  // Map from replication factors to copysets.
+  map<int32, Copysets> by_rf = 1 [(gogoproto.nullable) = false];
+  // Strategy used for store-copyset allocation.
+  CopysetStrategy strategy = 2;
+}
+
+// Copysets contains copysets for a particular replication factor.
+// If copysets based rebalancing is enabled, the replicas of a range will
+// be contained within a copy set. Each store belongs to a single copyset.
+// Copyset based rebalancing significantly improves failure tolerance.
+message Copysets {
+  // Map from CopysetID to a Copyset (set of stores in the copyset).
+  map<int32, Copyset> sets = 1 [(gogoproto.nullable) = false,
+      (gogoproto.castkey) = "CopysetID"];
+  // Replication factor of copy sets.
+  int32 replication_factor = 2;
+}
+
+// Copyset contains the set of stores belonging to the same copyset.
+message Copyset{
+  // Map of StoreIDs.
+  map<int32, bool> ids = 1 [
+      (gogoproto.castkey) = "github.com/cockroachdb/cockroach/pkg/roachpb.StoreID"];
+}

pkg/storage/copysets/doc.go

+// Copyright 2019 The Cockroach Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied. See the License for the specific language governing
+// permissions and limitations under the License.
+
+/*
+Package copysets proves an implementation of copysets presented in
+https://web.stanford.edu/~skatti/pubs/usenix13-copysets.pdf.
+
+Stores are divided into sets of nodes of size replication factor (for each
+replication factor) and ranges reside within a single copyset in steady state.
+This significantly reduces the probability of data loss in large clusters since
+as long as a quorum of nodes are alive within each copyset, there is no loss
+of data.
+*/
+package copysets