In some cases (specially when using a small cache size or a large database over…

In some cases (specially when using a small cache size or a large database over 1 GB) for some operations like ALTER TABLE the data was written before the transaction log entries, which could cause a corrupt database if the process was killed during the ALTER TABLE operation.

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

@@ -234,9 +234,10 @@ abstract class PageData extends Page {
     }
 
     public boolean canRemove() {
-        if (changeCount >= index.getPageStore().getChangeCount()) {
-            return false;
-        }
+int test;
+//        if (changeCount >= index.getPageStore().getChangeCount()) {
+//            return false;
+//        }
         return true;
     }
 

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

@@ -158,6 +158,11 @@ public class PageLog {
      */
     private BitSet usedLogPages;
 
+    /**
+     * This flag is set while freeing up pages.
+     */
+    private boolean freeing;
+
     PageLog(PageStore store) {
         this.store = store;
         dataBuffer = store.createData();
@@ -196,9 +201,20 @@ public class PageLog {
             currentDataPage = pageOut.getCurrentDataPageId();
             pageOut.freeReserved();
         }
+        try {
+            freeing = true;
+            int first = 0;
+            int loopDetect = 1024, loopCount = 0;
             PageStreamTrunk.Iterator it = new PageStreamTrunk.Iterator(store, firstTrunkPage);
             while (firstTrunkPage != 0 && firstTrunkPage < store.getPageCount()) {
                 PageStreamTrunk t = it.next();
+                if (loopCount++ >= loopDetect) {
+                    first = t.getPos();
+                    loopCount = 0;
+                    loopDetect *= 2;
+                } else if (first != 0 && t != null && first == t.getPos()) {
+                    throw DbException.throwInternalError("endless loop at " + t);
+                }
                 if (t == null) {
                     if (it.canDelete()) {
                         store.free(firstTrunkPage, false);
@@ -208,6 +224,9 @@ public class PageLog {
                 t.free(currentDataPage);
                 firstTrunkPage = t.getNextTrunk();
             }
+        } finally {
+            freeing = false;
+        }
     }
 
     /**
@@ -452,7 +471,7 @@ public class PageLog {
      * @param page the old page data
      */
     void addUndo(int pageId, Data page) {
-        if (undo.get(pageId)) {
+        if (undo.get(pageId) || freeing) {
             return;
         }
         if (trace.isDebugEnabled()) {

h2/src/main/org/h2/util/CacheLRU.java

@@ -168,6 +168,11 @@ public class CacheLRU implements Cache {
             }
         }
         if (changed.size() > 0) {
+int fixMaybeReplacesChangeCount;
+            if (!flushed) {
+                writer.flushLog();
+            }
+
             Collections.sort(changed);
             int max = maxMemory;
             try {

h2/src/test/org/h2/test/unit/TestCache.java

@@ -109,7 +109,7 @@ public class TestCache extends TestBase implements CacheWriter {
         for (int i = 0; i < 20; i++) {
             c.put(new Obj(i));
         }
-        assertEquals("0 1 2 3 ", out);
+        assertEquals("flush 0 flush 1 flush 2 flush 3 ", out);
     }
 
     /**

h2/src/test/org/h2/test/unit/TestPageStore.java

@@ -34,10 +34,12 @@ public class TestPageStore extends TestBase implements DatabaseEventListener {
      * @param a ignored
      */
     public static void main(String... a) throws Exception {
+        System.setProperty("h2.check2", "true");
         TestBase.createCaller().init().test();
     }
 
     public void test() throws Exception {
+        testWriteTransactionLogBeforeData();
         testDefrag();
         testInsertReverse();
         testInsertDelete();
@@ -66,6 +68,36 @@ public class TestPageStore extends TestBase implements DatabaseEventListener {
         deleteDb("pageStore");
     }
 
+    private void testWriteTransactionLogBeforeData() throws SQLException {
+        deleteDb("pageStore");
+        String url = getURL("pageStore;CACHE_SIZE=16;WRITE_DELAY=1000000", true);
+        Connection conn;
+        Statement stat;
+        conn = getConnection(url, getUser(), getPassword());
+        stat = conn.createStatement();
+        stat.execute("create table test(name varchar) as select space(100000)");
+        for (int i = 0; i < 100; i++) {
+            stat.execute("create table test" + i + "(id int) as select x from system_range(1, 1000)");
+        }
+        conn.close();
+        conn = getConnection(url, getUser(), getPassword());
+        stat = conn.createStatement();
+        stat.execute("drop table test0");
+        stat.execute("select * from test");
+        stat.execute("shutdown immediately");
+        try {
+            conn.close();
+        } catch (Exception e) {
+            // ignore
+        }
+        conn = getConnection(url, getUser(), getPassword());
+        stat = conn.createStatement();
+        for (int i = 1; i < 100; i++) {
+            stat.execute("select * from test" + i);
+        }
+        conn.close();
+    }
+
     private void testDefrag() throws SQLException {
         deleteDb("pageStore");
         Connection conn = getConnection("pageStore;LOG=0;UNDO_LOG=0;LOCK_MODE=0");