New experimental feature SHUTDOWN DEFRAG.

h2/src/main/org/h2/index/PageDataLeaf.java

@@ -538,13 +538,13 @@ public class PageDataLeaf extends PageData {
         p2.writeData();
         p2.data.truncate(index.getPageStore().getPageSize());
         store.update(p2);
-        store.free(getPos());
         if (parentPageId == ROOT) {
             index.setRootPageId(session, newPos);
         } else {
             PageDataNode p = (PageDataNode) store.getPage(parentPageId);
             p.moveChild(getPos(), newPos);
         }
+        store.free(getPos());
     }
 
     /**

h2/src/main/org/h2/store/Page.java

@@ -10,7 +10,6 @@ import java.lang.reflect.Array;
 import org.h2.engine.Session;
 import org.h2.util.CacheObject;
 
-
 /**
  * A page. Format:
  * <ul><li>0-3: parent page id (0 for root)
@@ -253,4 +252,13 @@ public abstract class Page extends CacheObject {
         }
     }
 
+    /**
+     * If this page can be moved. Transaction log and free-list pages can not.
+     *
+     * @return true if moving is allowed
+     */
+    public boolean canMove() {
+        return true;
+    }
+
 }

h2/src/main/org/h2/store/PageFreeList.java

@@ -222,4 +222,8 @@ public class PageFreeList extends Page {
         return false;
     }
 
+    public boolean canMove() {
+        return false;
+    }
+
 }

h2/src/main/org/h2/store/PageStore.java

@@ -520,24 +520,34 @@ public class PageStore implements CacheWriter {
                 }
             }
             recordPageReads = false;
+            int target = MIN_PAGE_COUNT - 1;
             for (int i = 0; i < recordedPagesList.size(); i++) {
                 writeBack();
-                cache.clear();
-                int a = MIN_PAGE_COUNT + i;
-                int b = recordedPagesList.get(i);
-                if (a == b) {
+                int source = recordedPagesList.get(i);
+                Page pageSource = getPage(source);
+                if (!pageSource.canMove()) {
+                    continue;
+                }
+                while (true) {
+                    Page pageTarget = getPage(++target);
+                    if (pageTarget == null || pageTarget.canMove()) {
+                        break;
+                    }
+                }
+                if (target == source) {
                     continue;
                 }
                 int temp = getFirstFree();
                 if (temp == -1) {
                     DbException.throwInternalError("no free page for defrag");
                 }
-                swap(a, b, temp);
-                int index = recordedPagesList.indexOf(a);
+                cache.clear();
+                swap(source, target, temp);
+                int index = recordedPagesList.indexOf(target);
                 if (index >= 0) {
-                    recordedPagesList.set(index, b);
+                    recordedPagesList.set(index, source);
                 }
-                recordedPagesList.set(i, a);
+                recordedPagesList.set(i, target);
             }
             recordedPagesList = null;
             recordedPages = null;
@@ -606,17 +616,23 @@ public class PageStore implements CacheWriter {
         Page pageA = null;
         if (isUsed(a)) {
             pageA = getPage(a);
+            if (pageA != null) {
                 pageA.moveTo(systemSession, free);
+            }
             free(a);
         }
         if (isUsed(b)) {
             Page pageB = getPage(b);
+            if (pageB != null) {
                 pageB.moveTo(systemSession, a);
+            }
             free(b);
         }
         if (pageA != null) {
             f = getPage(free);
+            if (f != null) {
                 f.moveTo(systemSession, b);
+            }
             free(free);
         }
     }

h2/src/main/org/h2/store/PageStreamData.java

@@ -165,4 +165,8 @@ public class PageStreamData extends Page {
         return DATA_START;
     }
 
+    public boolean canMove() {
+        return false;
+    }
+
 }
\ No newline at end of file

h2/src/main/org/h2/store/PageStreamTrunk.java

@@ -287,4 +287,8 @@ public class PageStreamTrunk extends Page {
         return "page[" + getPos() + "] stream trunk key:" + logKey + " next:" + nextTrunk;
     }
 
+    public boolean canMove() {
+        return false;
+    }
+
 }