Unify mutable segment name across the codebase to avoid confusion.

src/Playground/Benchmark/ZoneTree1.cs

@@ -57,7 +57,7 @@ public static void Insert(WriteAheadLogMode mode, int count)
 
         if (mode == WriteAheadLogMode.None)
         {
-            zoneTree.Maintenance.MoveSegmentZeroForward();
+            zoneTree.Maintenance.MoveMutableSegmentForward();
             zoneTree.Maintenance.StartMergeOperation()?.Join();
         }
         basicMaintainer.CompleteRunningTasks(); 
@@ -181,7 +181,7 @@ public static void InsertSingleAndMerge(WriteAheadLogMode mode, int count, int k
             zoneTree.Upsert(key, key + key);
             ++key;
         }
-        zoneTree.Maintenance.MoveSegmentZeroForward();
+        zoneTree.Maintenance.MoveMutableSegmentForward();
         zoneTree.Maintenance.StartMergeOperation()?.Join();
 
         basicMaintainer.CompleteRunningTasks();

src/Playground/Benchmark/ZoneTree2.cs

@@ -62,7 +62,7 @@ public static void Insert(WriteAheadLogMode mode, int count)
         stopWatch.Restart();
         if (mode == WriteAheadLogMode.None)
         {
-            zoneTree.Maintenance.MoveSegmentZeroForward();
+            zoneTree.Maintenance.MoveMutableSegmentForward();
             zoneTree.Maintenance.StartMergeOperation()?.Join();
         }
         basicMaintainer.CompleteRunningTasks();

src/Playground/Benchmark/ZoneTree3.cs

@@ -61,7 +61,7 @@ public static void Insert(WriteAheadLogMode mode, int count)
 
         if (mode == WriteAheadLogMode.None)
         {
-            zoneTree.Maintenance.ZoneTree.Maintenance.MoveSegmentZeroForward();
+            zoneTree.Maintenance.ZoneTree.Maintenance.MoveMutableSegmentForward();
             zoneTree.Maintenance.ZoneTree.Maintenance.StartMergeOperation()?.Join();
         }
 

src/ZoneTree.UnitTests/AtomicUpdateTests.cs

@@ -26,7 +26,7 @@ public void IntIntAtomicIncrement(WriteAheadLogMode walMode)
         {
             data.Upsert(i, i + i);
         }
-        data.Maintenance.MoveSegmentZeroForward();
+        data.Maintenance.MoveMutableSegmentForward();
         data.Maintenance.StartMergeOperation().Join();
         var random = new Random();
         var off = -1;
@@ -69,7 +69,7 @@ public void IntIntAtomicIncrement(WriteAheadLogMode walMode)
             });
         }
 
-        data.Maintenance.MoveSegmentZeroForward();
+        data.Maintenance.MoveMutableSegmentForward();
         data.Maintenance.StartMergeOperation().Join();
         data.TryGet(counterKey, out var finalValue);
         Assert.That(finalValue, Is.EqualTo(off));

src/ZoneTree.UnitTests/BottomSegmentMergeTests.cs

@@ -26,7 +26,7 @@ public void IntIntBottomMerge()
             zoneTree.Upsert(i, i + i);
             if (i % p == p - 1)
             {
-                m.MoveSegmentZeroForward();
+                m.MoveMutableSegmentForward();
                 m.StartMergeOperation().Join();
                 for (var j = 0; j < p - 10; ++j)
                 {

src/ZoneTree.UnitTests/FixedSizeKeyAndValueTests.cs

@@ -21,7 +21,7 @@ public void IntIntTreeTest()
         {
             data.Upsert(i, i + i);
         }
-        data.Maintenance.MoveSegmentZeroForward();
+        data.Maintenance.MoveMutableSegmentForward();
         data.Maintenance.StartMergeOperation().Join();
         for (var i = 0; i < 2000; ++i)
         {
@@ -51,7 +51,7 @@ public void IntStringTreeTest()
         {
             data.Upsert(i, (i + i).ToString());
         }
-        data.Maintenance.MoveSegmentZeroForward();
+        data.Maintenance.MoveMutableSegmentForward();
         data.Maintenance.StartMergeOperation().Join();
         for (var i = 0; i < n; ++i)
         {
@@ -83,7 +83,7 @@ public void StringIntTreeTest(bool useSparseArray)
         {
             data.Upsert(i.ToString(), i + i);
         }
-        data.Maintenance.MoveSegmentZeroForward();
+        data.Maintenance.MoveMutableSegmentForward();
         data.Maintenance.StartMergeOperation().Join();
         if (useSparseArray)
             data.Maintenance.DiskSegment.InitSparseArray(200);
@@ -118,7 +118,7 @@ public void StringStringTreeTest(bool useSparseArray)
         {
             data.Upsert(i.ToString(), (i + i).ToString());
         }
-        data.Maintenance.MoveSegmentZeroForward();
+        data.Maintenance.MoveMutableSegmentForward();
         data.Maintenance.StartMergeOperation().Join();
         if (useSparseArray)
             data.Maintenance.DiskSegment.InitSparseArray(200);

src/ZoneTree.UnitTests/IteratorTests.cs

@@ -66,7 +66,7 @@ public void IntIntIterator()
 
         Assert.That(reverseIterator.Next(), Is.False);
 
-        zoneTree.Maintenance.MoveSegmentZeroForward();
+        zoneTree.Maintenance.MoveMutableSegmentForward();
         zoneTree.Maintenance.StartMergeOperation().Join();
 
         Assert.That(zoneTree.Maintenance.DiskSegment.Length, Is.EqualTo(b - 4));
@@ -157,7 +157,7 @@ public void IntIntIteratorSeek()
         Assert.That(reverseIterator.CurrentKey, Is.EqualTo(b - 2));
         Assert.That(zoneTree.Count(), Is.EqualTo(b - 4));
 
-        zoneTree.Maintenance.MoveSegmentZeroForward();
+        zoneTree.Maintenance.MoveMutableSegmentForward();
         zoneTree.Maintenance.StartMergeOperation().Join();
 
         Assert.That(zoneTree.Maintenance.DiskSegment.Length, Is.EqualTo(b - 4));
@@ -211,7 +211,7 @@ public void IntIntIteratorReflectNewInserts()
              * This is not a bug. Callers can always double check
              * with TryGetKey() if they want to read most recent values
              * for every key they read from iteration.
-             * Auto refresh property was made for SegmentZeroMoveForward
+             * Auto refresh property was made for MutableSegmentMoveForward
              * event. A manual refresh also works but it is expensive to call
              * for every key.
              */

src/ZoneTree.UnitTests/StringTreeTests.cs

@@ -41,7 +41,7 @@ public void NullStringKeyTest()
             ++j;
         }
         var maintenance = zoneTree.Maintenance;
-        maintenance.MoveSegmentZeroForward();
+        maintenance.MoveMutableSegmentForward();
         maintenance.StartMergeOperation()?.Join();
 
         using var iterator2 = zoneTree.CreateIterator();

src/ZoneTree/Core/ZoneTree.Iterators.cs

@@ -6,7 +6,7 @@ namespace Tenray.ZoneTree.Core;
 public sealed partial class ZoneTree<TKey, TValue> : IZoneTree<TKey, TValue>, IZoneTreeMaintenance<TKey, TValue>
 {
     public SegmentCollection CollectSegments(
-        bool includeSegmentZero,
+        bool includeMutableSegment,
         bool includeDiskSegment,
         bool includeBottomSegments)
     {
@@ -15,8 +15,8 @@ public SegmentCollection CollectSegments(
             {
                 var roSegments = ReadOnlySegmentQueue.ToArray();
                 var seekableIterators = new List<ISeekableIterator<TKey, TValue>>();
-                if (includeSegmentZero)
-                    seekableIterators.Add(SegmentZero.GetSeekableIterator());
+                if (includeMutableSegment)
+                    seekableIterators.Add(MutableSegment.GetSeekableIterator());
 
                 var readOnlySegmentsArray = roSegments.Select(x => x.GetSeekableIterator()).ToArray();
                 seekableIterators.AddRange(readOnlySegmentsArray.Reverse());
@@ -63,7 +63,7 @@ public class SegmentCollection
     public IZoneTreeIterator<TKey, TValue> CreateIterator(
         IteratorType iteratorType, bool includeDeletedRecords)
     {
-        var includeSegmentZero = iteratorType is not IteratorType.Snapshot and
+        var includeMutableSegment = iteratorType is not IteratorType.Snapshot and
             not IteratorType.ReadOnlyRegion;
 
         var iterator = new ZoneTreeIterator<TKey, TValue>(
@@ -73,13 +73,13 @@ public IZoneTreeIterator<TKey, TValue> CreateIterator(
             autoRefresh: iteratorType == IteratorType.AutoRefresh,
             isReverseIterator: false,
             includeDeletedRecords,
-            includeSegmentZero: includeSegmentZero,
+            includeMutableSegment: includeMutableSegment,
             includeDiskSegment: true,
             includeBottomSegments: true);
 
         if (iteratorType == IteratorType.Snapshot)
         {
-            MoveSegmentZeroForward();
+            MoveMutableSegmentForward();
             iterator.Refresh();
             iterator.WaitUntilReadOnlySegmentsBecomeFullyFrozen();
         }
@@ -94,7 +94,7 @@ public IZoneTreeIterator<TKey, TValue> CreateIterator(
     public IZoneTreeIterator<TKey, TValue> CreateReverseIterator(
         IteratorType iteratorType, bool includeDeletedRecords)
     {
-        var includeSegmentZero = iteratorType is not IteratorType.Snapshot and
+        var includeMutableSegment = iteratorType is not IteratorType.Snapshot and
             not IteratorType.ReadOnlyRegion;
 
         var iterator = new ZoneTreeIterator<TKey, TValue>(
@@ -104,13 +104,13 @@ public IZoneTreeIterator<TKey, TValue> CreateReverseIterator(
             autoRefresh: iteratorType == IteratorType.AutoRefresh,
             isReverseIterator: true,
             includeDeletedRecords,
-            includeSegmentZero: includeSegmentZero,
+            includeMutableSegment: includeMutableSegment,
             includeDiskSegment: true,
             includeBottomSegments: true);
 
         if (iteratorType == IteratorType.Snapshot)
         {
-            MoveSegmentZeroForward();
+            MoveMutableSegmentForward();
             iterator.Refresh();
             iterator.WaitUntilReadOnlySegmentsBecomeFullyFrozen();
         }
@@ -136,7 +136,7 @@ public IZoneTreeIterator<TKey, TValue> CreateReadOnlySegmentsIterator(bool autoR
             autoRefresh: autoRefresh,
             isReverseIterator: false,
             includeDeletedRecords,
-            includeSegmentZero: false,
+            includeMutableSegment: false,
             includeDiskSegment: false,
             includeBottomSegments: false);
         return iterator;
@@ -158,7 +158,7 @@ public IZoneTreeIterator<TKey, TValue>
             autoRefresh: autoRefresh,
             isReverseIterator: false,
             includeDeletedRecords,
-            includeSegmentZero: true,
+            includeMutableSegment: true,
             includeDiskSegment: false,
             includeBottomSegments: false);
         return iterator;

src/ZoneTree/Core/ZoneTree.Merge.cs

@@ -15,39 +15,39 @@ public sealed partial class ZoneTree<TKey, TValue> : IZoneTree<TKey, TValue>, IZ
     /// The movement only occurs
     /// if the current segment zero is the given segment zero.
     /// </summary>
-    /// <param name="segmentZero">The segment zero to move forward.</param>
-    void MoveSegmentZeroForward(IMutableSegment<TKey, TValue> segmentZero)
+    /// <param name="mutableSegment">The segment zero to move forward.</param>
+    void MoveMutableSegmentForward(IMutableSegment<TKey, TValue> mutableSegment)
     {
         lock (AtomicUpdateLock)
         {
             // move segment zero only if
             // the given segment zero is the current segment zero (not already moved)
             // and it is not frozen.
-            if (segmentZero.IsFrozen || segmentZero != SegmentZero)
+            if (mutableSegment.IsFrozen || mutableSegment != MutableSegment)
                 return;
 
             //Don't move empty segment zero.
-            var c = segmentZero.Length;
+            var c = mutableSegment.Length;
             if (c == 0)
                 return;
 
-            segmentZero.Freeze();
-            ReadOnlySegmentQueue.Enqueue(segmentZero);
-            MetaWal.EnqueueReadOnlySegment(segmentZero.SegmentId);
+            mutableSegment.Freeze();
+            ReadOnlySegmentQueue.Enqueue(mutableSegment);
+            MetaWal.EnqueueReadOnlySegment(mutableSegment.SegmentId);
 
-            SegmentZero = new MutableSegment<TKey, TValue>(
+            MutableSegment = new MutableSegment<TKey, TValue>(
                 Options, IncrementalIdProvider.NextId(),
-                segmentZero.OpIndexProvider);
-            MetaWal.NewSegmentZero(SegmentZero.SegmentId);
+                mutableSegment.OpIndexProvider);
+            MetaWal.NewMutableSegment(MutableSegment.SegmentId);
         }
-        OnSegmentZeroMovedForward?.Invoke(this);
+        OnMutableSegmentMovedForward?.Invoke(this);
     }
 
-    public void MoveSegmentZeroForward()
+    public void MoveMutableSegmentForward()
     {
         lock (AtomicUpdateLock)
         {
-            MoveSegmentZeroForward(SegmentZero);
+            MoveMutableSegmentForward(MutableSegment);
         }
     }
 

src/ZoneTree/Core/ZoneTree.ReadWrite.cs

@@ -9,9 +9,9 @@ public sealed partial class ZoneTree<TKey, TValue> : IZoneTree<TKey, TValue>, IZ
     public bool ContainsKey(in TKey key)
     {
         TValue value;
-        if (SegmentZero.ContainsKey(key))
+        if (MutableSegment.ContainsKey(key))
         {
-            if (SegmentZero.TryGet(key, out value))
+            if (MutableSegment.TryGet(key, out value))
                 return !IsValueDeleted(value);
         }
 
@@ -85,7 +85,7 @@ bool TryGetFromReadonlySegments(in TKey key, out TValue value)
 
     public bool TryGet(in TKey key, out TValue value)
     {
-        if (SegmentZero.TryGet(key, out value))
+        if (MutableSegment.TryGet(key, out value))
         {
             return !IsValueDeleted(value);
         }
@@ -97,7 +97,7 @@ public bool TryGetAndUpdate(in TKey key, out TValue value, ValueUpdaterDelegate<
         if (IsReadOnly)
             throw new ZoneTreeIsReadOnlyException();
 
-        if (SegmentZero.TryGet(key, out value))
+        if (MutableSegment.TryGet(key, out value))
         {
             if (IsValueDeleted(value))
                 return false;
@@ -122,7 +122,7 @@ public bool TryAtomicGetAndUpdate(in TKey key, out TValue value, ValueUpdaterDel
 
         lock (AtomicUpdateLock)
         {
-            if (SegmentZero.TryGet(key, out value))
+            if (MutableSegment.TryGet(key, out value))
             {
                 if (IsValueDeleted(value))
                     return false;
@@ -175,39 +175,39 @@ public bool TryAtomicAddOrUpdate(in TKey key, in TValue valueToAdd, ValueUpdater
         if (IsReadOnly)
             throw new ZoneTreeIsReadOnlyException();
         AddOrUpdateResult status;
-        IMutableSegment<TKey, TValue> segmentZero;
+        IMutableSegment<TKey, TValue> mutableSegment;
         while (true)
         {
             lock (AtomicUpdateLock)
             {
-                segmentZero = SegmentZero;
-                if (segmentZero.IsFrozen)
+                mutableSegment = MutableSegment;
+                if (mutableSegment.IsFrozen)
                 {
                     status = AddOrUpdateResult.RETRY_SEGMENT_IS_FULL;
                 }
-                else if (segmentZero.TryGet(in key, out var existing))
+                else if (mutableSegment.TryGet(in key, out var existing))
                 {
                     if (!valueUpdater(ref existing))
                         return false;
-                    status = segmentZero.Upsert(key, existing);
+                    status = mutableSegment.Upsert(key, existing);
                 }
                 else if (TryGetFromReadonlySegments(in key, out existing))
                 {
                     if (!valueUpdater(ref existing))
                         return false;
-                    status = segmentZero.Upsert(key, existing);
+                    status = mutableSegment.Upsert(key, existing);
                 }
                 else
                 {
-                    status = segmentZero.Upsert(key, valueToAdd);
+                    status = mutableSegment.Upsert(key, valueToAdd);
                 }
             }
             switch (status)
             {
                 case AddOrUpdateResult.RETRY_SEGMENT_IS_FROZEN:
                     continue;
                 case AddOrUpdateResult.RETRY_SEGMENT_IS_FULL:
-                    MoveSegmentZeroForward(segmentZero);
+                    MoveMutableSegmentForward(mutableSegment);
                     continue;
                 default:
                     return status == AddOrUpdateResult.ADDED;
@@ -231,14 +231,14 @@ public void Upsert(in TKey key, in TValue value)
             throw new ZoneTreeIsReadOnlyException();
         while (true)
         {
-            var segmentZero = SegmentZero;
-            var status = segmentZero.Upsert(key, value);
+            var mutableSegment = MutableSegment;
+            var status = mutableSegment.Upsert(key, value);
             switch (status)
             {
                 case AddOrUpdateResult.RETRY_SEGMENT_IS_FROZEN:
                     continue;
                 case AddOrUpdateResult.RETRY_SEGMENT_IS_FULL:
-                    MoveSegmentZeroForward(segmentZero);
+                    MoveMutableSegmentForward(mutableSegment);
                     continue;
                 default:
                     return;
@@ -262,15 +262,15 @@ public void ForceDelete(in TKey key)
             throw new ZoneTreeIsReadOnlyException();
         while (true)
         {
-            var segmentZero = SegmentZero;
-            var status = segmentZero.Delete(key);
+            var mutableSegment = MutableSegment;
+            var status = mutableSegment.Delete(key);
             switch (status)
             {
                 case AddOrUpdateResult.RETRY_SEGMENT_IS_FROZEN:
                     ForceDelete(key);
                     continue;
                 case AddOrUpdateResult.RETRY_SEGMENT_IS_FULL:
-                    MoveSegmentZeroForward(segmentZero);
+                    MoveMutableSegmentForward(mutableSegment);
                     ForceDelete(key);
                     continue;
                 default: return;