rangedesciter: carve out library for range desc iteration

Informs cockroachdb#87503; pure code-movement. Going to use it in future commits as
part of multi-tenant replication reports (cockroachdb#89987) where we'll need to
iterate over the set of range descriptors.

Release note: None

pkg/BUILD.bazel

@@ -585,6 +585,7 @@ ALL_TESTS = [
     "//pkg/util/quantile:quantile_test",
     "//pkg/util/quotapool:quotapool_test",
     "//pkg/util/randutil:randutil_test",
+    "//pkg/util/rangedesciter:rangedesciter_test",
     "//pkg/util/retry:retry_test",
     "//pkg/util/ring:ring_test",
     "//pkg/util/schedulerlatency:schedulerlatency_test",
@@ -2020,6 +2021,8 @@ GO_TARGETS = [
     "//pkg/util/quotapool:quotapool_test",
     "//pkg/util/randutil:randutil",
     "//pkg/util/randutil:randutil_test",
+    "//pkg/util/rangedesciter:rangedesciter",
+    "//pkg/util/rangedesciter:rangedesciter_test",
     "//pkg/util/retry:retry",
     "//pkg/util/retry:retry_test",
     "//pkg/util/ring:ring",
@@ -2994,6 +2997,7 @@ GET_X_DATA_TARGETS = [
     "//pkg/util/quantile:get_x_data",
     "//pkg/util/quotapool:get_x_data",
     "//pkg/util/randutil:get_x_data",
+    "//pkg/util/rangedesciter:get_x_data",
     "//pkg/util/retry:get_x_data",
     "//pkg/util/ring:get_x_data",
     "//pkg/util/schedulerlatency:get_x_data",

pkg/server/BUILD.bazel

@@ -257,6 +257,7 @@ go_library(
         "//pkg/util/pprofutil",
         "//pkg/util/protoutil",
         "//pkg/util/quotapool",
+        "//pkg/util/rangedesciter",
         "//pkg/util/retry",
         "//pkg/util/schedulerlatency",
         "//pkg/util/stop",

pkg/server/server_sql.go

@@ -111,6 +111,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/util/mon"
 	"github.com/cockroachdb/cockroach/pkg/util/netutil"
 	"github.com/cockroachdb/cockroach/pkg/util/netutil/addr"
+	"github.com/cockroachdb/cockroach/pkg/util/rangedesciter"
 	"github.com/cockroachdb/cockroach/pkg/util/stop"
 	"github.com/cockroachdb/cockroach/pkg/util/syncutil"
 	"github.com/cockroachdb/cockroach/pkg/util/timeutil"
@@ -1004,9 +1005,10 @@ func newSQLServer(ctx context.Context, cfg sqlServerArgs) (*SQLServer, error) {
 		var systemDeps upgrade.SystemDeps
 		if codec.ForSystemTenant() {
 			c = upgradecluster.New(upgradecluster.ClusterConfig{
-				NodeLiveness: nodeLiveness,
-				Dialer:       cfg.nodeDialer,
-				DB:           cfg.db,
+				NodeLiveness:      nodeLiveness,
+				Dialer:            cfg.nodeDialer,
+				RangeDescIterator: rangedesciter.New(cfg.db),
+				DB:                cfg.db,
 			})
 			systemDeps = upgrade.SystemDeps{
 				Cluster:    c,

pkg/upgrade/system_upgrade.go

@@ -94,30 +94,6 @@ type Cluster interface {
 	// just be the `Migrate` request, with code added within [1] to do the
 	// specific things intended for the specified version.
 	//
-	// It's important to note that the closure is being executed in the context of
-	// a distributed transaction that may be automatically retried. So something
-	// like the following is an anti-pattern:
-	//
-	//     processed := 0
-	//     _ = h.IterateRangeDescriptors(...,
-	//         func(descriptors ...roachpb.RangeDescriptor) error {
-	//             processed += len(descriptors) // we'll over count if retried
-	//             log.Infof(ctx, "processed %d ranges", processed)
-	//         },
-	//     )
-	//
-	// Instead we allow callers to pass in a callback to signal on every attempt
-	// (including the first). This lets us salvage the example above:
-	//
-	//     var processed int
-	//     init := func() { processed = 0 }
-	//     _ = h.IterateRangeDescriptors(..., init,
-	//         func(descriptors ...roachpb.RangeDescriptor) error {
-	//             processed += len(descriptors)
-	//             log.Infof(ctx, "processed %d ranges", processed)
-	//         },
-	//     )
-	//
 	// [1]: pkg/kv/kvserver/batch_eval/cmd_migrate.go
 	IterateRangeDescriptors(
 		ctx context.Context,

pkg/upgrade/upgradecluster/BUILD.bazel

@@ -11,7 +11,6 @@ go_library(
     importpath = "github.com/cockroachdb/cockroach/pkg/upgrade/upgradecluster",
     visibility = ["//visibility:public"],
     deps = [
-        "//pkg/keys",
         "//pkg/kv",
         "//pkg/kv/kvserver/liveness/livenesspb",
         "//pkg/roachpb",
@@ -20,6 +19,7 @@ go_library(
         "//pkg/util/ctxgroup",
         "//pkg/util/log",
         "//pkg/util/quotapool",
+        "//pkg/util/rangedesciter",
         "@com_github_cockroachdb_errors//:errors",
         "@com_github_cockroachdb_redact//:redact",
         "@org_golang_google_grpc//:go_default_library",
@@ -30,23 +30,19 @@ go_test(
     name = "upgradecluster_test",
     size = "small",
     srcs = [
-        "client_test.go",
         "helper_test.go",
         "main_test.go",
         "nodes_test.go",
     ],
     args = ["-test.timeout=55s"],
     embed = [":upgradecluster"],
     deps = [
-        "//pkg/keys",
-        "//pkg/kv/kvserver",
         "//pkg/roachpb",
         "//pkg/rpc",
         "//pkg/security/securityassets",
         "//pkg/security/securitytest",
         "//pkg/server",
         "//pkg/server/serverpb",
-        "//pkg/sql/tests",
         "//pkg/testutils",
         "//pkg/testutils/serverutils",
         "//pkg/testutils/testcluster",

pkg/upgrade/upgradecluster/cluster.go

@@ -14,7 +14,6 @@ package upgradecluster
 import (
 	"context"
 
-	"github.com/cockroachdb/cockroach/pkg/keys"
 	"github.com/cockroachdb/cockroach/pkg/kv"
 	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/liveness/livenesspb"
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
@@ -23,7 +22,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/util/ctxgroup"
 	"github.com/cockroachdb/cockroach/pkg/util/log"
 	"github.com/cockroachdb/cockroach/pkg/util/quotapool"
-	"github.com/cockroachdb/errors"
+	"github.com/cockroachdb/cockroach/pkg/util/rangedesciter"
 	"github.com/cockroachdb/redact"
 	"google.golang.org/grpc"
 )
@@ -42,6 +41,9 @@ type ClusterConfig struct {
 	// Dialer constructs connections to other nodes.
 	Dialer NodeDialer
 
+	// RangeDescIterator iterates through all range descriptors.
+	RangeDescIterator rangedesciter.Iterator
+
 	// DB provides access the kv.DB instance backing the cluster.
 	//
 	// TODO(irfansharif): We could hide the kv.DB instance behind an interface
@@ -143,50 +145,5 @@ func (c *Cluster) ForEveryNode(
 func (c *Cluster) IterateRangeDescriptors(
 	ctx context.Context, blockSize int, init func(), fn func(...roachpb.RangeDescriptor) error,
 ) error {
-	return c.c.DB.Txn(ctx, func(ctx context.Context, txn *kv.Txn) error {
-		// Inform the caller that we're starting a fresh attempt to page in
-		// range descriptors.
-		init()
-
-		// Iterate through meta{1,2} to pull out all the range descriptors.
-		var lastRangeIDInMeta1 roachpb.RangeID
-		return txn.Iterate(ctx, keys.MetaMin, keys.MetaMax, blockSize,
-			func(rows []kv.KeyValue) error {
-				descriptors := make([]roachpb.RangeDescriptor, 0, len(rows))
-				var desc roachpb.RangeDescriptor
-				for _, row := range rows {
-					err := row.ValueProto(&desc)
-					if err != nil {
-						return errors.Wrapf(err, "unable to unmarshal range descriptor from %s", row.Key)
-					}
-
-					// In small enough clusters it's possible for the same range
-					// descriptor to be stored in both meta1 and meta2. This
-					// happens when some range spans both the meta and the user
-					// keyspace. Consider when r1 is [/Min,
-					// /System/NodeLiveness); we'll store the range descriptor
-					// in both /Meta2/<r1.EndKey> and in /Meta1/KeyMax[1].
-					//
-					// As part of iterator we'll de-duplicate this descriptor
-					// away by checking whether we've seen it before in meta1.
-					// Since we're scanning over the meta range in sorted
-					// order, it's enough to check against the last range
-					// descriptor we've seen in meta1.
-					//
-					// [1]: See kvserver.rangeAddressing.
-					if desc.RangeID == lastRangeIDInMeta1 {
-						continue
-					}
-
-					descriptors = append(descriptors, desc)
-					if keys.InMeta1(keys.RangeMetaKey(desc.StartKey)) {
-						lastRangeIDInMeta1 = desc.RangeID
-					}
-				}
-
-				// Invoke fn with the current chunk (of size ~blockSize) of
-				// range descriptors.
-				return fn(descriptors...)
-			})
-	})
+	return c.c.RangeDescIterator.Iterate(ctx, blockSize, init, fn)
 }

pkg/util/rangedesciter/BUILD.bazel

@@ -0,0 +1,39 @@
+load("//build/bazelutil/unused_checker:unused.bzl", "get_x_data")
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "rangedesciter",
+    srcs = ["rangedesciter.go"],
+    importpath = "github.com/cockroachdb/cockroach/pkg/util/rangedesciter",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//pkg/keys",
+        "//pkg/kv",
+        "//pkg/roachpb",
+        "@com_github_cockroachdb_errors//:errors",
+    ],
+)
+
+go_test(
+    name = "rangedesciter_test",
+    srcs = [
+        "main_test.go",
+        "rangedesciter_test.go",
+    ],
+    args = ["-test.timeout=295s"],
+    deps = [
+        ":rangedesciter",
+        "//pkg/keys",
+        "//pkg/kv/kvserver",
+        "//pkg/roachpb",
+        "//pkg/security/securityassets",
+        "//pkg/security/securitytest",
+        "//pkg/server",
+        "//pkg/sql/tests",
+        "//pkg/testutils/serverutils",
+        "//pkg/testutils/testcluster",
+        "//pkg/util/leaktest",
+    ],
+)
+
+get_x_data(name = "get_x_data")

pkg/util/rangedesciter/main_test.go

@@ -0,0 +1,31 @@
+// 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 rangedesciter_test
+
+import (
+	"os"
+	"testing"
+
+	"github.com/cockroachdb/cockroach/pkg/security/securityassets"
+	"github.com/cockroachdb/cockroach/pkg/security/securitytest"
+	"github.com/cockroachdb/cockroach/pkg/server"
+	"github.com/cockroachdb/cockroach/pkg/testutils/serverutils"
+	"github.com/cockroachdb/cockroach/pkg/testutils/testcluster"
+)
+
+func TestMain(m *testing.M) {
+	securityassets.SetLoader(securitytest.EmbeddedAssets)
+	serverutils.InitTestServerFactory(server.TestServerFactory)
+	serverutils.InitTestClusterFactory(testcluster.TestClusterFactory)
+	os.Exit(m.Run())
+}
+
+//go:generate ../../util/leaktest/add-leaktest.sh *_test.go