inner-1457:small memory leak when read from disk

Signed-off-by: dcy <dcy10000@gmail.com>

src/main/java/com/actiontech/dble/backend/mysql/store/diskbuffer/ResultDiskBuffer.java

@@ -222,6 +222,10 @@ public abstract class ResultDiskBuffer implements ResultExternal {
             }
         }
 
+        public void clear() {
+            pool.recycle(readBuffer);
+        }
+
         private void checkReadBuffer(int offset) {
             // if offset is 0,then expend buffer; else set offset to 0,compact
             // buffer

src/main/java/com/actiontech/dble/backend/mysql/store/diskbuffer/SortedResultDiskBuffer.java

@@ -133,6 +133,14 @@ public class SortedResultDiskBuffer extends ResultDiskBuffer {
         resetHeap();
     }
 
+    @Override
+    public void close() {
+        for (ResultDiskTape tape : tapes) {
+            tape.clear();
+        }
+        super.close();
+    }
+
     protected void resetHeap() {
         if (heap == null)
             heap = new ArrayMinHeap<>(tapes.size(), this.heapCmp);

src/main/java/com/actiontech/dble/backend/mysql/store/diskbuffer/UnSortedResultDiskBuffer.java

@@ -68,6 +68,12 @@ public class UnSortedResultDiskBuffer extends ResultDiskBuffer {
         mainTape.readBuffer.clear();
     }
 
+    @Override
+    public void close() {
+        mainTape.clear();
+        super.close();
+    }
+
     @Override
     public RowDataPacket next() {
         file.seek(mainTape.pos);