File intermediate buffers should be flushed on all flushes.

src/ZoneTree/Segments/Disk/CompressedFileRandomAccessDevice.cs

@@ -139,7 +139,7 @@ public sealed class CompressedFileRandomAccessDevice : IRandomAccessDevice
         CompressedBlockPositions.Add(offset);
         CompressedBlockLengths.Add(compressedBytes.Length);
         FileStream.Write(compressedBytes);
-        FileStream.Flush();
+        FileStream.Flush(true);
         DecompressedBlocks.TryRemove(nextBlock.BlockIndex, out _);
         ++NextBlockIndex;
         LastBlockLength = 0;
@@ -219,7 +219,7 @@ public sealed class CompressedFileRandomAccessDevice : IRandomAccessDevice
         DecompressedBlocks.Clear();
         if (FileStream == null)
             return;
-        FileStream.Flush();
+        FileStream.Flush(true);
         FileStream.Dispose();
         FileStream = null;
         if (Writable)
@@ -274,7 +274,7 @@ public sealed class CompressedFileRandomAccessDevice : IRandomAccessDevice
         }
         bw.Write(positions.Count);
         bw.Write(offset);
-        FileStream.Flush();
+        FileStream.Flush(true);
     }
 
     (List<long> positions, List<int> lengths) ReadCompressedBlockPositionsAndLengths()

src/ZoneTree/Segments/Disk/FileRandomAccessDevice.cs

@@ -46,7 +46,7 @@ public sealed class FileRandomAccessDevice : IRandomAccessDevice
     {
         var pos = FileStream.Position;
         FileStream.Write(bytes);
-        FileStream.Flush();
+        FileStream.Flush(true);
         return pos;
     }
 
@@ -81,7 +81,7 @@ public sealed class FileRandomAccessDevice : IRandomAccessDevice
     {
         if (FileStream == null)
             return;
-        FileStream.Flush();
+        FileStream.Flush(true);
         FileStream.Dispose();
         FileStream = null;
         if (Writable)

src/ZoneTree/WAL/CompressedFileStream.cs

@@ -160,7 +160,7 @@ public sealed class CompressedFileStream : Stream, IDisposable
             BinaryChunkWriter.Write(tailBlock.Length);
             var bytes = tailBlock.GetBytes(0, tailBlock.Length);
             BinaryChunkWriter.Write(bytes);
-            TailStream.Flush();
+            TailStream.Flush(true);
             LastWrittenTailIndex = tailBlock.BlockIndex;
             LastWrittenTailLength = tailBlock.Length;
         }

src/ZoneTree/WAL/FileSystemWriteAheadLog.cs

@@ -133,7 +133,7 @@ public sealed class FileSystemWriteAheadLog<TKey, TValue> : IWriteAheadLog<TKey,
     private void Flush()
     {
         if (FileStream.CanWrite)
-            FileStream.Flush();
+            FileStream.Flush(true);
     }
 
     public long ReplaceWriteAheadLog(TKey[] keys, TValue[] values, bool disableBackup)
@@ -147,7 +147,7 @@ public sealed class FileSystemWriteAheadLog<TKey, TValue> : IWriteAheadLog<TKey,
                         FilePath + ".full",
                         () =>
                         {
-                            FileStream.Flush();
+                            FileStream.Flush(true);
                             FileStream.Seek(0, SeekOrigin.Begin);
                             var existingLength = (int)FileStream.Length;
                             var bytes = new byte[existingLength];

src/ZoneTree/WAL/IncrementalLogAppender.cs

@@ -51,7 +51,7 @@ public static class IncrementalLogAppender
             fs.Write(BitConverter.GetBytes(fs.Length));
             fs.Write(BitConverter.GetBytes(fs.Length));
             fs.Write(BitConverter.GetBytes(fs.Length));
-            fs.Flush();
+            fs.Flush(true);
         }
 
         // first append the additional data.
@@ -59,17 +59,17 @@ public static class IncrementalLogAppender
 
         fs.Seek(0, SeekOrigin.End);
         fs.Write(bytes);
-        fs.Flush();
+        fs.Flush(true);
 
         // now write the file length-stamps.
         // what happens if a crash happens with partial write of the fs Length?
         // To prevent that, we write and flush the length-stamp three times with separate flushes..
         fs.Position = 0;
         fs.Write(BitConverter.GetBytes(fs.Length));
-        fs.Flush();
+        fs.Flush(true);
         fs.Write(BitConverter.GetBytes(fs.Length));
-        fs.Flush();
+        fs.Flush(true);
         fs.Write(BitConverter.GetBytes(fs.Length));
-        fs.Flush();
+        fs.Flush(true);
     }
 }