utilccl: cache license decoding

Previously, the `utilccl` package would decode the license from the the
base64-encoded Protobuf representation in settings every time it was
needed, which was sufficient for its uses. However, recently there's
been a need to check whether enterprise features are enabled in hot
paths (e.g. with follower reads as seen in cockroachdb#62447), making the decoding
cost too great.

This patch adds `cluster.Settings.Cache` as a shared cache, and uses it
to cache decoded licenses with a private key type.

Release note: None

pkg/ccl/utilccl/license_check.go

@@ -62,6 +62,10 @@ const (
 var errEnterpriseRequired = pgerror.New(pgcode.CCLValidLicenseRequired,
 	"a valid enterprise license is required")
 
+// licenseCacheKey is used to cache licenses in cluster.Settings.Cache,
+// keeping the entries private.
+type licenseCacheKey string
+
 // TestingEnableEnterprise allows overriding the license check in tests.
 func TestingEnableEnterprise() func() {
 	before := atomic.LoadInt32(&testingEnterprise)
@@ -112,19 +116,12 @@ func init() {
 func TimeToEnterpriseLicenseExpiry(
 	ctx context.Context, st *cluster.Settings, asOf time.Time,
 ) (time.Duration, error) {
-	var lic *licenseccl.License
-	// FIXME(tschottdorf): see whether it makes sense to cache the decoded
-	// license.
-	if str := enterpriseLicense.Get(&st.SV); str != "" {
-		var err error
-		if lic, err = decode(str); err != nil {
-			return 0, err
-		}
-	} else {
-		return 0, nil
+	license, err := getLicense(st)
+	if err != nil || license == nil {
+		return 0, err
 	}
 
-	expiration := timeutil.Unix(lic.ValidUntilUnixSec, 0)
+	expiration := timeutil.Unix(license.ValidUntilUnixSec, 0)
 	return expiration.Sub(asOf), nil
 }
 
@@ -134,28 +131,41 @@ func checkEnterpriseEnabledAt(
 	if atomic.LoadInt32(&testingEnterprise) == testingEnterpriseEnabled {
 		return nil
 	}
-	var lic *licenseccl.License
-	// FIXME(tschottdorf): see whether it makes sense to cache the decoded
-	// license.
-	if str := enterpriseLicense.Get(&st.SV); str != "" {
-		var err error
-		if lic, err = decode(str); err != nil {
-			return err
-		}
+	license, err := getLicense(st)
+	if err != nil {
+		return err
 	}
-	return check(lic, at, cluster, org, feature, withDetails)
+	return check(license, at, cluster, org, feature, withDetails)
 }
 
-func getLicenseType(st *cluster.Settings) (string, error) {
+// getLicense fetches the license from the given settings, using Settings.Cache
+// to cache the decoded license (if any). The returned license must not be
+// modified by the caller.
+func getLicense(st *cluster.Settings) (*licenseccl.License, error) {
 	str := enterpriseLicense.Get(&st.SV)
 	if str == "" {
-		return "None", nil
+		return nil, nil
 	}
-	lic, err := decode(str)
+	cacheKey := licenseCacheKey(str)
+	if cachedLicense, ok := st.Cache.Load(cacheKey); ok {
+		return cachedLicense.(*licenseccl.License), nil
+	}
+	license, err := decode(str)
+	if err != nil {
+		return nil, err
+	}
+	st.Cache.Store(cacheKey, license)
+	return license, nil
+}
+
+func getLicenseType(st *cluster.Settings) (string, error) {
+	license, err := getLicense(st)
 	if err != nil {
 		return "", err
+	} else if license == nil {
+		return "None", nil
 	}
-	return lic.Type.String(), nil
+	return license.Type.String(), nil
 }
 
 // decode attempts to read a base64 encoded License.
@@ -164,7 +174,7 @@ func decode(s string) (*licenseccl.License, error) {
 	if err != nil {
 		return nil, pgerror.WithCandidateCode(err, pgcode.Syntax)
 	}
-	return lic, err
+	return lic, nil
 }
 
 // check returns an error if the license is empty or not currently valid. If

pkg/ccl/utilccl/license_check_test.go

@@ -63,7 +63,7 @@ func TestSettingAndCheckingLicense(t *testing.T) {
 		if err := updater.Set("enterprise.license", tc.lic, "s"); err != nil {
 			t.Fatal(err)
 		}
-		err := checkEnterpriseEnabledAt(st, tc.checkTime, tc.checkCluster, "", "")
+		err := checkEnterpriseEnabledAt(st, tc.checkTime, tc.checkCluster, "", "", true)
 		if !testutils.IsError(err, tc.err) {
 			l, _ := decode(tc.lic)
 			t.Fatalf("%d: lic %v, update by %T, checked by %s at %s, got %q", i, l, updater, tc.checkCluster, tc.checkTime, err)

pkg/ccl/utilccl/license_test.go

@@ -83,7 +83,7 @@ func TestLicense(t *testing.T) {
 			}
 		}
 		if err := check(
-			lic, tc.checkTime, tc.checkCluster, tc.checkOrg, "",
+			lic, tc.checkTime, tc.checkCluster, tc.checkOrg, "", true,
 		); !testutils.IsError(err, tc.err) {
 			t.Fatalf("%d: lic for %s to %s, checked by %s at %s.\n got %q", i,
 				tc.grantedTo, tc.expiration, tc.checkCluster, tc.checkTime, err)
@@ -108,7 +108,7 @@ func TestExpiredLicenseLanguage(t *testing.T) {
 		Type:              licenseccl.License_Evaluation,
 		ValidUntilUnixSec: 1,
 	}
-	err := check(lic, timeutil.Now(), uuid.MakeV4(), "", "RESTORE")
+	err := check(lic, timeutil.Now(), uuid.MakeV4(), "", "RESTORE", true)
 	expected := "Use of RESTORE requires an enterprise license. Your evaluation license expired on " +
 		"January 1, 1970. If you're interested in getting a new license, please contact " +
 		"[email protected] and we can help you out."

pkg/settings/cluster/cluster_settings.go

@@ -12,6 +12,7 @@ package cluster
 
 import (
 	"context"
+	"sync"
 	"sync/atomic"
 
 	"github.com/cockroachdb/cockroach/pkg/clusterversion"
@@ -51,6 +52,10 @@ type Settings struct {
 	// Setting the active cluster version has a very specific, intended usage
 	// pattern. Look towards the interface itself for more commentary.
 	Version clusterversion.Handle
+
+	// Cache can be used for arbitrary caching, e.g. to cache decoded
+	// enterprises licenses for utilccl.CheckEnterpriseEnabled().
+	Cache sync.Map
 }
 
 // TelemetryOptOut is a place for controlling whether to opt out of telemetry or not.