Review comments.

modules/core/src/main/java/org/apache/ignite/internal/processors/cache/transactions/IgniteTxAdapter.java

@@ -2028,6 +2028,8 @@ protected Object readResolve() throws ObjectStreamException {
     /**
      * Make counters accumulated during transaction visible outside of transaciton.
      */
+    // TODO: Why everything is concurrent? If only one thread changes, then use volatile.
+    // TODO: If already protected, then remove concurrent collections.
     protected void applyTxCounters() {
         Map<Integer, ? extends Map<Integer, AtomicLong>> sizeDeltas = txCounters.sizeDeltas();
 

modules/core/src/main/java/org/apache/ignite/internal/processors/cache/transactions/IgniteTxLocalStateAdapter.java

@@ -57,6 +57,7 @@ protected final void onTxEnd(GridCacheContext cacheCtx, IgniteInternalTx tx, boo
 
     /** {@inheritDoc} */
     @Override public void touchPartition(int cacheId, int partId) {
+        // TODO: Race? Or remove concurrent collections.
         if (touchedParts == null)
             touchedParts = new ConcurrentHashMap<>();
 

modules/core/src/main/java/org/apache/ignite/internal/processors/cache/transactions/TxCounters.java

@@ -27,6 +27,7 @@
 /**
  * Values which should be tracked during transaction execution and applied on commit.
  */
+// TODO: Can we remove "touched" and use counter (cache->part) mappings?
 public class TxCounters {
     /** Size changes for cache partitions made by transaction */
     private final ConcurrentMap<Integer, ConcurrentMap<Integer, AtomicLong>> sizeDeltas = new ConcurrentHashMap<>();

modules/indexing/src/test/java/org/apache/ignite/internal/processors/cache/mvcc/CacheMvccSizeTest.java

@@ -35,6 +35,14 @@
 /**
  *
  */
+// TODO: Minimize cache restarts
+// TODO: No tests for UPDATE
+// TODO: Tests for updates on the same key? INSERT/DELETE/INSERT, etc.
+// TODO: Merge operation tests
+// TODO: Write conflict test
+// TODO: Concurrent tests
+// TODO: Tests for cache API: failing tests or separate ticket
+
 public class CacheMvccSizeTest extends CacheMvccAbstractTest {
     /** {@inheritDoc} */
     @Override protected CacheMode cacheMode() {