MVStore: up to 65535 open transactions are now supported. Previously, the limit…

MVStore: up to 65535 open transactions are now supported. Previously, the limit was at most 65535 transactions between the oldest open and the newest open transaction (which was quite a strange limit).

h2/src/docsrc/html/advanced.html

@@ -1621,6 +1621,7 @@ This database has the following known limitations:
     In that case files are split into files of 1 GB by default.
     An example database URL is: <code>jdbc:h2:split:~/test</code>.
 </li><li>The maximum number of rows per table is 2^64.
+</li><li>The maximum number of open transactions is 65535.
 </li><li>Main memory requirements: The larger the database, the more main memory is required.
     With the current storage mechanism (the page store),
     the minimum main memory required is around 1 MB for each 8 GB database file size.

h2/src/docsrc/html/changelog.html

@@ -17,7 +17,10 @@ Change Log
 <h1>Change Log</h1>
 
 <h2>Next Version (unreleased)</h2>
-<ul><li>The default limit for in-place LOB objects was changed from 128 to 256 bytes.
+<ul><li>MVStore: up to 65535 open transactions are now supported.
+    Previously, the limit was at most 65535 transactions between the oldest open and the
+    newest open transaction (which was quite a strange limit).
+</li><li>The default limit for in-place LOB objects was changed from 128 to 256 bytes.
     This is because each read creates a reference to a LOB, and maintaining the references
     is a big overhead. With the higher limit, less references are needed.
 </li><li>Tables without columns didn't work. 

h2/src/main/org/h2/mvstore/DataUtils.java

@@ -89,9 +89,9 @@ public class DataUtils {
     public static final int ERROR_TRANSACTION_LOCKED = 101;
 
     /**
-     * A very old transaction is still open.
+     * There are too many open transactions.
      */
-    public static final int ERROR_TRANSACTION_STILL_OPEN = 102;
+    public static final int ERROR_TOO_MANY_OPEN_TRANSACTIONS = 102;
 
     /**
      * The transaction store is in an illegal state (for example, not yet

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

@@ -7,6 +7,7 @@ package org.h2.mvstore.db;
 
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
+import java.util.BitSet;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
@@ -57,9 +58,9 @@ public class TransactionStore {
 
     private final DataType dataType;
 
-    private boolean init;
+    private final BitSet openTransactions = new BitSet();
     
-    private int lastTransactionId;
+    private boolean init;
 
     private int maxTransactionId = 0xffff;
 
@@ -119,8 +120,10 @@ public class TransactionStore {
         }
         synchronized (undoLog) {
             if (undoLog.size() > 0) {
-                Long key = undoLog.firstKey();
-                lastTransactionId = getTransactionId(key);
+                for (Long key : undoLog.keySet()) {
+                    int transactionId = getTransactionId(key);
+                    openTransactions.set(transactionId);
+                }
             }
         }
     }
@@ -225,10 +228,14 @@ public class TransactionStore {
                     DataUtils.ERROR_TRANSACTION_ILLEGAL_STATE,
                     "Not initialized");
         }
-        int transactionId = ++lastTransactionId;
-        if (lastTransactionId >= maxTransactionId) {
-            lastTransactionId = 0;
+        int transactionId = openTransactions.nextClearBit(1);
+        if (transactionId > maxTransactionId) {
+            throw DataUtils.newIllegalStateException(
+                    DataUtils.ERROR_TOO_MANY_OPEN_TRANSACTIONS,
+                    "There are {0} open transactions",
+                    transactionId - 1);
         }
+        openTransactions.set(transactionId);
         int status = Transaction.STATUS_OPEN;
         return new Transaction(this, transactionId, status, null, 0);
     }
@@ -263,7 +270,7 @@ public class TransactionStore {
             if (logId == 0) {
                 if (undoLog.containsKey(undoKey)) {
                     throw DataUtils.newIllegalStateException(
-                            DataUtils.ERROR_TRANSACTION_STILL_OPEN,
+                            DataUtils.ERROR_TOO_MANY_OPEN_TRANSACTIONS,
                             "An old transaction with the same id " +
                             "is still open: {0}",
                             t.getId());
@@ -435,6 +442,7 @@ public class TransactionStore {
             preparedTransactions.remove(t.getId());
         }
         t.setStatus(Transaction.STATUS_CLOSED);
+        openTransactions.clear(t.transactionId);
         if (store.getAutoCommitDelay() == 0) {
             store.commit();
             return;

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

@@ -49,6 +49,7 @@ public class TestMVTableEngine extends TestBase {
 
     @Override
     public void test() throws Exception {
+        testManyTransactions();
         testAppendOnly();
         testLowRetentionTime();
         testOldAndNew();
@@ -82,6 +83,23 @@ public class TestMVTableEngine extends TestBase {
         testSimple();
     }
     
+    private void testManyTransactions() throws Exception {
+        deleteDb("testManyTransactions");        
+        Connection conn = getConnection("testManyTransactions");
+        Statement stat = conn.createStatement();
+        stat.execute("create table test()");
+        conn.setAutoCommit(false);
+        stat.execute("insert into test values()");
+
+        Connection conn2 = getConnection("testManyTransactions");
+        Statement stat2 = conn2.createStatement();          
+        for (long i = 0; i < 100000; i++) {
+            stat2.execute("insert into test values()");
+        }
+        conn2.close();
+        conn.close();
+    }
+
     private void testAppendOnly() throws Exception {
         deleteDb("testAppendOnly");
         Connection conn = getConnection(

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

@@ -154,15 +154,21 @@ public class TestTransactionStore extends TestBase {
         ts = new TransactionStore(s);
         ts.init();
         ts.setMaxTransactionId(16);
+        ArrayList<Transaction> openList = new ArrayList<Transaction>();
         for (int i = 0, j = 1; i < 64; i++) {
             Transaction t = ts.begin();
+            openList.add(t);
             assertEquals(j, t.getId());
-            t.commit();
             j++;
             if (j > 16) {
                 j = 1;
             }
+            if (openList.size() >= 16) {
+                t = openList.remove(0);
+                t.commit();
+            }
         }
+
         s = MVStore.open(null);
         ts = new TransactionStore(s);
         ts.init();
@@ -170,10 +176,10 @@ public class TestTransactionStore extends TestBase {
         ArrayList<Transaction> fifo = New.arrayList();
         int open = 0;
         for (int i = 0; i < 64; i++) {
-            Transaction t = ts.begin();
+            Transaction t = null;
             if (open >= 16) {
                 try {
-                    t.openMap("data").put(i, i);
+                    t = ts.begin();
                     fail();
                 } catch (IllegalStateException e) {
                     // expected - too many open
@@ -182,9 +188,10 @@ public class TestTransactionStore extends TestBase {
                 first.commit();
                 open--;
             }
+            t = ts.begin();
+            t.openMap("data").put(i, i);
             fifo.add(t);
             open++;
-            t.openMap("data").put(i, i);
         }
         s.close();
     }
@@ -514,6 +521,8 @@ public class TestTransactionStore extends TestBase {
         assertEquals("first transaction", txOld.getName());
         txOld.prepare();
         assertEquals(Transaction.STATUS_PREPARED, txOld.getStatus());
+        txOld = list.get(1);
+        txOld.commit();
         s.commit();
         s.close();
 
@@ -522,6 +531,7 @@ public class TestTransactionStore extends TestBase {
         ts.init();
         tx = ts.begin();
         m = tx.openMap("test");
+        m.put("3", "Test");
         assertEquals(2, tx.getId());
         list = ts.getOpenTransactions();
         assertEquals(2, list.size());