Small performance improvements.

h2/src/main/org/h2/command/Prepared.java

@@ -345,7 +345,7 @@ public abstract class Prepared {
      * @param rowNumber the row number
      */
     protected void setCurrentRowNumber(int rowNumber) throws SQLException {
-        if ((rowScanCount++ & 127) == 0) {
+        if ((++rowScanCount & 127) == 0) {
             checkCanceled();
         }
         this.currentRowNumber = rowNumber;

h2/src/main/org/h2/command/dml/Delete.java

@@ -64,7 +64,7 @@ public class Delete extends Prepared {
             }
             int rowScanCount = 0;
             for (rows.reset(); rows.hasNext();) {
-                if ((rowScanCount++ & 127) == 0) {
+                if ((++rowScanCount & 127) == 0) {
                     checkCanceled();
                 }
                 Row row = rows.next();

h2/src/main/org/h2/expression/Comparison.java

@@ -227,11 +227,15 @@ public class Comparison extends Condition {
             }
             return ValueBoolean.get(result);
         }
-        l = l.convertTo(dataType);
-        Value r = right.getValue(session).convertTo(dataType);
-        if (l == ValueNull.INSTANCE || r == ValueNull.INSTANCE) {
+        if (l == ValueNull.INSTANCE) {
+            return ValueNull.INSTANCE;
+        }
+        Value r = right.getValue(session);
+        if (r == ValueNull.INSTANCE) {
             return ValueNull.INSTANCE;
         }
+        l = l.convertTo(dataType);
+        r = r.convertTo(dataType);
         boolean result = compareNotNull(database, l, r, compareType);
         return ValueBoolean.get(result);
     }

h2/src/main/org/h2/table/Table.java

@@ -382,7 +382,7 @@ public abstract class Table extends SchemaObjectBase {
         // remove the old rows
         int rowScanCount = 0;
         for (rows.reset(); rows.hasNext();) {
-            if ((rowScanCount++ & 127) == 0) {
+            if ((++rowScanCount & 127) == 0) {
                 prepared.checkCanceled();
             }
             Row o = rows.next();
@@ -392,7 +392,7 @@ public abstract class Table extends SchemaObjectBase {
         }
         // add the new rows
         for (rows.reset(); rows.hasNext();) {
-            if ((rowScanCount++ & 127) == 0) {
+            if ((++rowScanCount & 127) == 0) {
                 prepared.checkCanceled();
             }
             rows.next();

h2/src/main/org/h2/table/TableData.java

@@ -68,6 +68,13 @@ public class TableData extends Table implements RecordReader {
     private boolean containsLargeObject;
     private PageDataIndex mainIndex;
 
+    /**
+     * True if one thread ever was waiting to lock this table. This is to avoid
+     * calling notifyAll if no session was ever waiting to lock this table. If
+     * set, the flag stays. In theory, it could be reset, however not sure when.
+     */
+    private boolean waitForLock;
+
     public TableData(CreateTableData data) throws SQLException {
         super(data.schema, data.id, data.tableName, data.persistIndexes, data.persistData);
         Column[] cols = new Column[data.columns.size()];
@@ -507,6 +514,7 @@ public class TableData extends Table implements RecordReader {
                 if (sleep == 0) {
                     sleep = 1;
                 }
+                waitForLock = true;
                 database.wait(sleep);
             } catch (InterruptedException e) {
                 // ignore
@@ -643,7 +651,7 @@ public class TableData extends Table implements RecordReader {
             // TODO lock: maybe we need we fifo-queue to make sure nobody
             // starves. check what other databases do
             synchronized (database) {
-                if (database.getSessionCount() > 1) {
+                if (database.getSessionCount() > 1 && waitForLock) {
                     database.notifyAll();
                 }
             }