Partial port of commit 011a35b0a

Author: paulirwin

src/Lucene.Net/Index/FlushByRamOrCountsPolicy.cs

@@ -97,7 +97,7 @@ public override void OnInsert(DocumentsWriterFlushControl control, ThreadState s
                 {
                     if (m_infoStream.IsEnabled("FP"))
                     {
-                        m_infoStream.Message("FP", "flush: activeBytes=" + control.ActiveBytes + " deleteBytes=" + control.DeleteBytesUsed + " vs limit=" + limit);
+                        m_infoStream.Message("FP", "trigger flush: activeBytes=" + control.ActiveBytes + " deleteBytes=" + control.DeleteBytesUsed + " vs limit=" + limit);
                     }
                     MarkLargestWriterPending(control, state, totalRam);
                 }

src/Lucene.Net/Index/FlushPolicy.cs

@@ -122,19 +122,28 @@ protected virtual ThreadState FindLargestNonPendingWriter(DocumentsWriterFlushCo
             ThreadState maxRamUsingThreadState = perThreadState;
             if (Debugging.AssertsEnabled) Debugging.Assert(!perThreadState.flushPending, "DWPT should have flushed");
             using IEnumerator<ThreadState> activePerThreadsIterator = control.AllActiveThreadStates();
+            int count = 0;
             while (activePerThreadsIterator.MoveNext())
             {
                 ThreadState next = activePerThreadsIterator.Current;
                 if (!next.flushPending)
                 {
                     long nextRam = next.bytesUsed;
-                    if (nextRam > maxRamSoFar && next.dwpt.NumDocsInRAM > 0)
+                    if (nextRam > 0 && next.dwpt.NumDocsInRAM > 0)
                     {
-                        maxRamSoFar = nextRam;
-                        maxRamUsingThreadState = next;
+                        count++;
+                        if (nextRam > maxRamSoFar)
+                        {
+                            maxRamSoFar = nextRam;
+                            maxRamUsingThreadState = next;
+                        }
                     }
                 }
             }
+            if (m_infoStream.IsEnabled("FP"))
+            {
+                m_infoStream.Message("FP", $"{count} in-use non-flushing threads states");
+            }
             if (Debugging.AssertsEnabled) Debugging.Assert(AssertMessage("set largest ram consuming thread pending on lower watermark"));
             return maxRamUsingThreadState;
         }