Merge cockroachdb#93901

93901: kvstorage: add package r=pavelkalinnikov a=tbg

We need a place for logic and testing of the engine interactions for the
separate raft log to live. This is this place.

Epic: CRDB-220

Co-authored-by: Tobias Grieger <[email protected]>

.github/CODEOWNERS

@@ -224,6 +224,7 @@
 /pkg/kv/kvserver/kvadmission/           @cockroachdb/kv-prs
 /pkg/kv/kvserver/kvserverbase/          @cockroachdb/kv-prs
 /pkg/kv/kvserver/kvserverpb/            @cockroachdb/kv-prs
+/pkg/kv/kvserver/kvstorage/             @cockroachdb/repl-prs
 /pkg/kv/kvserver/liveness/              @cockroachdb/kv-prs
 /pkg/kv/kvserver/logstore/              @cockroachdb/repl-prs
 /pkg/kv/kvserver/loqrecovery/           @cockroachdb/repl-prs

pkg/BUILD.bazel

@@ -1183,6 +1183,7 @@ GO_TARGETS = [
     "//pkg/kv/kvserver/kvadmission:kvadmission",
     "//pkg/kv/kvserver/kvserverbase:kvserverbase",
     "//pkg/kv/kvserver/kvserverpb:kvserverpb",
+    "//pkg/kv/kvserver/kvstorage:kvstorage",
     "//pkg/kv/kvserver/liveness/livenesspb:livenesspb",
     "//pkg/kv/kvserver/liveness:liveness",
     "//pkg/kv/kvserver/liveness:liveness_test",
@@ -2529,6 +2530,7 @@ GET_X_DATA_TARGETS = [
     "//pkg/kv/kvserver/kvadmission:get_x_data",
     "//pkg/kv/kvserver/kvserverbase:get_x_data",
     "//pkg/kv/kvserver/kvserverpb:get_x_data",
+    "//pkg/kv/kvserver/kvstorage:get_x_data",
     "//pkg/kv/kvserver/liveness:get_x_data",
     "//pkg/kv/kvserver/liveness/livenesspb:get_x_data",
     "//pkg/kv/kvserver/logstore:get_x_data",

pkg/kv/kvserver/kvstorage/BUILD.bazel

@@ -0,0 +1,11 @@
+load("//build/bazelutil/unused_checker:unused.bzl", "get_x_data")
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "kvstorage",
+    srcs = ["doc.go"],
+    importpath = "github.com/cockroachdb/cockroach/pkg/kv/kvserver/kvstorage",
+    visibility = ["//visibility:public"],
+)
+
+get_x_data(name = "get_x_data")

pkg/kv/kvserver/kvstorage/doc.go

@@ -0,0 +1,22 @@
+// Copyright 2022 The Cockroach Authors.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+// Package kvstorage houses the logic that manages the on-disk state for the
+// Replicas housed on a Store. Replicas store data in two storage.Engine
+// instances, which are optionally (and at the time of writing, always)
+// identical. One Engine, the "log storage", stores Raft-related state (such as
+// the raft log), while the other engine stores the replicated keyspace.
+//
+// The ability to separate log and state machine opens up performance
+// improvements, but results in a more complex lifecycle where operations that
+// need to update both the state machine and the raft state require more complex
+// recovery in the event of an ill-timed crash. Encapsulating and testing this
+// logic is the raison d'être for this package.
+package kvstorage