diff --git a/platform/lang-impl/src/com/intellij/util/indexing/IndexingStamp.java b/platform/lang-impl/src/com/intellij/util/indexing/IndexingStamp.java
index f2d9a781512f..b90ff635a1ef 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/IndexingStamp.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/IndexingStamp.java
@@ -68,6 +68,9 @@ public final class IndexingStamp {
   }
 
   private static final int INDEXING_STAMP_CACHE_CAPACITY = SystemProperties.getIntProperty("index.timestamp.cache.size", 100);
+  //MAYBE RC: do we still need in-memory cache (fileId->Timestamps)? With new fast-attributes + fast enumerator
+  //          access may be fast enough even without caching -- or, at least, it may be worth to cache enumerator
+  //          records (which is 100-1000 records at max) only
   private static final ConcurrentIntObjectMap<Timestamps> ourTimestampsCache =
     ConcurrentCollectionFactory.createConcurrentIntObjectMap();
   private static final BlockingQueue<Integer> ourFinishedFiles = new ArrayBlockingQueue<>(INDEXING_STAMP_CACHE_CAPACITY);
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/TimestampsImmutable.kt b/platform/lang-impl/src/com/intellij/util/indexing/TimestampsImmutable.kt
index 8f1e666cf874..fb6fb9369ebb 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/TimestampsImmutable.kt
+++ b/platform/lang-impl/src/com/intellij/util/indexing/TimestampsImmutable.kt
@@ -33,6 +33,8 @@ class TimestampsImmutable {
   }
 
   companion object {
+    //FIXME RC: this call to application makes us use ApplicationRule in tests for TimestampsImmutable -- which
+    //          introduce completely superficial coupling, because TimestampsImmutable logic has nothing to do with application
     private val IS_UNIT_TEST = ApplicationManager.getApplication().isUnitTestMode()
 
     @JvmField
@@ -117,7 +119,7 @@ class TimestampsImmutable {
         assert(dominatingIndexStamp == DataInputOutputUtil.timeBase) {
           "dominatingIndexStamp=$dominatingIndexStamp != timeBase=${DataInputOutputUtil.timeBase}"
         }
-        dominatingIndexStamp = 0
+        dominatingIndexStamp = 0 //MAYBE RC: return EMPTY?
       }
       return TimestampsImmutable(dominatingIndexStamp, outdatedIndices, upToDateIndexIds)
     }
@@ -200,7 +202,6 @@ class TimestampsImmutable {
     val indexStamps = Object2LongOpenHashMap<ID<*, *>>()
 
     upToDateIndexIds.forEach { indexUniqueId ->
-      //RC: .findById() takes 1/4 of total the method time -- mostly spent on CHMap lookup.
       val id = ID.findById(indexUniqueId)
       if (id != null && id !is StubIndexKey<*, *>) {
         val stamp = IndexVersion.getIndexCreationStamp(id)