validate: use immutable descriptors only

The descriptor validation logic will accept any implementation of
catalog.Descriptor be it mutable or immutable, it doesn't care. However,
using mutable implementations can have a significant performance impact
especially in the case of tables, where every column or index or
constraint lookup will lead to the cache being regenerated for the whole
descriptor.

This commit fixes this by having validate.Validate replace any mutable
descriptor instances it encounters with immutable copies. This doesn't
change anything except performance.

Fixes #95827.

Release note: None

pkg/sql/catalog/internal/validate/validate.go

@@ -58,6 +58,15 @@ func Validate(
 	targetLevel catalog.ValidationLevel,
 	descriptors ...catalog.Descriptor,
 ) catalog.ValidationErrors {
+	for i, d := range descriptors {
+		// Replace mutable descriptors with immutable copies. Validation is
+		// read-only in any case, and using immutables can have a significant
+		// impact on performance when validating tables due to columns, indexes,
+		// and so forth being cached.
+		if mut, ok := d.(catalog.MutableDescriptor); ok {
+			descriptors[i] = mut.ImmutableCopy()
+		}
+	}
 	vea := validationErrorAccumulator{
 		ValidationTelemetry: telemetry,
 		targetLevel:         targetLevel,
@@ -409,9 +418,17 @@ func (cs *collectorState) getMissingDescs(
 		return nil, err
 	}
 	for _, desc := range resps {
-		if desc != nil {
-			cs.vdg.descriptors[desc.GetID()] = desc
+		if desc == nil {
+			continue
+		}
+		if mut, ok := desc.(catalog.MutableDescriptor); ok {
+			// Replace mutable descriptors with immutable copies. Validation is
+			// read-only in any case, and using immutables can have a significant
+			// impact on performance when validating tables due to columns, indexes,
+			// and so forth being cached.
+			desc = mut.ImmutableCopy()
 		}
+		cs.vdg.descriptors[desc.GetID()] = desc
 	}
 	return resps, nil
 }