MVStore: concurrent changes to the same row could result in the exception "The…

MVStore: concurrent changes to the same row could result in the exception "The transaction log might be corrupt for key ...". This could only be reproduced with 3 or more threads.

h2/src/main/org/h2/mvstore/db/TransactionStore.java

@@ -46,7 +46,7 @@ public class TransactionStore {
      * is not possible). Log entries are written before the data is changed
      * (write-ahead).
      * <p>
-     * Key: [ opId ], value: [ mapId, key, oldValue ].
+     * Key: opId, value: [ mapId, key, oldValue ].
      */
     final MVMap<Long, Object[]> undoLog;
 
@@ -223,12 +223,15 @@ public class TransactionStore {
      * @return the transaction
      */
     public synchronized Transaction begin() {
+
+        int transactionId;
+        int status;
         if (!init) {
             throw DataUtils.newIllegalStateException(
                     DataUtils.ERROR_TRANSACTION_ILLEGAL_STATE,
                     "Not initialized");
         }
-        int transactionId = openTransactions.nextClearBit(1);
+        transactionId = openTransactions.nextClearBit(1);
         if (transactionId > maxTransactionId) {
             throw DataUtils.newIllegalStateException(
                     DataUtils.ERROR_TOO_MANY_OPEN_TRANSACTIONS,
@@ -236,7 +239,7 @@ public class TransactionStore {
                     transactionId - 1);
         }
         openTransactions.set(transactionId);
-        int status = Transaction.STATUS_OPEN;
+        status = Transaction.STATUS_OPEN;
         return new Transaction(this, transactionId, status, null, 0);
     }
 
@@ -1232,35 +1235,13 @@ public class TransactionStore {
                 if (d == null) {
                     // this entry should be committed or rolled back
                     // in the meantime (the transaction might still be open)
+                    // or it might be changed again in a different
+                    // transaction (possibly one with the same id)
                     data = map.get(key);
-                    if (data != null && data.operationId == id) {
-                        // the transaction was not committed correctly
-                        throw DataUtils.newIllegalStateException(
-                                DataUtils.ERROR_TRANSACTION_CORRUPT,
-                                "The transaction log might be corrupt for key {0}",
-                                key);
-                    }
                 } else {
                     data = (VersionedValue) d[2];
                 }
-                // verify this is either committed,
-                // or the same transaction and earlier
-                if (data != null) {
-                    long id2 = data.operationId;
-                    if (id2 != 0) {
-                        int tx2 = getTransactionId(id2);
-                        if (tx2 != tx) {
-                            // a different transaction - ok
-                        } else if (getLogId(id2) > getLogId(id)) {
-                            // newer than before
-                            break;
-                        }
-                    }
-                }
             }
-            throw DataUtils.newIllegalStateException(
-                    DataUtils.ERROR_TRANSACTION_CORRUPT,
-                    "The transaction log might be corrupt for key {0}", key);
         }
 
         /**

h2/src/test/org/h2/test/store/TestTransactionStore.java

@@ -45,6 +45,7 @@ public class TestTransactionStore extends TestBase {
     @Override
     public void test() throws Exception {
         FileUtils.createDirectories(getBaseDir());
+        testConcurrentAddRemove();
         testConcurrentAdd();
         testCountWithOpenTransactions();
         testConcurrentUpdate();
@@ -61,6 +62,47 @@ public class TestTransactionStore extends TestBase {
         testCompareWithPostgreSQL();
     }
 
+    private void testConcurrentAddRemove() throws InterruptedException {
+        MVStore s = MVStore.open(null);
+        int threadCount = 3;
+        final int keyCount = 2;
+        final TransactionStore ts = new TransactionStore(s);
+        ts.init();
+
+        final Random r = new Random(1);
+
+        Task[] tasks = new Task[threadCount];
+        for (int i = 0; i < threadCount; i++) {
+            Task task = new Task() {
+
+                @Override
+                public void call() throws Exception {
+                    TransactionMap<Integer, Integer> map = null;
+                    while (!stop) {
+                        Transaction tx = ts.begin();
+                        map = tx.openMap("data");
+                        int k = r.nextInt(keyCount);
+                        try {
+                            map.remove(k);
+                            map.put(k, r.nextInt());
+                        } catch (IllegalStateException e) {
+                            // ignore and retry
+                        }
+                        tx.commit();
+                    }
+                }
+
+            };
+            task.execute();
+            tasks[i] = task;
+        }
+        Thread.sleep(1000);
+        for (Task t : tasks) {
+            t.get();
+        }
+        s.close();
+    }
+
     private void testConcurrentAdd() {
         MVStore s;
         s = MVStore.open(null);