New system property h2.selectForUpdateMvcc, the default is false (the feature is disabled).

h2/src/docsrc/html/changelog.html

@@ -18,7 +18,9 @@ Change Log
 <h1>Change Log</h1>
 
 <h2>Next Version (unreleased)</h2>
-<ul><li>Profiler: improved message if there was no stack trace.
+<ul><li>New system property h2.selectForUpdateMvcc, the default is false (the feature is disabled).
+    When enabled, SELECT ... FOR UPDATE only locks the selected rows in the MVCC mode.
+</li><li>Profiler: improved message if there was no stack trace.
 </li><li>The H2 Console can now be used within another application, in a frame or iframe. Issue 197.
 </li><li>Recover tool: the statistics section now includes page type counts again.
 </li><li>Queries with multiple IN(...) conditions sometimes return the wrong results when there was a multi-column index for the column.

h2/src/docsrc/html/roadmap.html

@@ -23,9 +23,10 @@ See also <a href="build.html#providing_patches">Providing Patches</a>.
 </p>
 
 <h2>Version 1.3.x: Planned Changes</h2>
-<ul><li>Lob storage: enable the system property h2.lobInDatabase by default.
-</li><li>Automatic ANALYZE: set the system property h2.analyzeAuto to 2000.
-</li><li>Enable h2.functionsInSchema.
+<ul><li>Enable h2.lobInDatabase (store CLOB and BLOB in the database file).
+</li><li>Set h2.analyzeAuto to 2000 (automatic ANALYZE).
+</li><li>Enable h2.functionsInSchema (allow to store functions in a schema).
+</li><li>Enable h2.selectForUpdateMvcc (MVCC and SELECT FOR UPDATE).
 </li></ul>
 
 <h2>Priority 1</h2>
@@ -38,7 +39,6 @@ See also <a href="build.html#providing_patches">Providing Patches</a>.
 
 <h2>Priority 2</h2>
 <ul><li>Improve test code coverage.
-</li><li>MVCC: select for update should only lock the selected rows.
 </li><li>Test multi-threaded in-memory db access
 </li><li>Option to shutdown all the running servers (on the same VM).
 </li><li>Full outer joins.
@@ -468,6 +468,8 @@ See also <a href="build.html#providing_patches">Providing Patches</a>.
 </li><li>Database file name suffix: a way to use no or a different suffix (for example using a slash).
 </li><li>Database file name suffix: should only have one dot by default. Example: .h2db
 </li><li>Issue 196: Function based indexes
+</li><li>Fix the disk space leak (killing the process at the exact right moment will increase
+    the disk space usage; this space is not re-used). See TestDiskSpaceLeak.java
 </li></ul>
 
 <h2>Not Planned</h2>

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

@@ -73,7 +73,7 @@ public class Select extends Query {
     private HashMap<Expression, Object> currentGroup;
     private int havingIndex;
     private boolean isGroupQuery, isGroupSortedQuery;
-    private boolean isForUpdate;
+    private boolean isForUpdate, isForUpdateMvcc;
     private double cost;
     private boolean isQuickAggregateQuery, isDistinctQuery;
     private boolean isPrepared, checkInit;
@@ -492,6 +492,9 @@ public class Select extends Query {
                     Expression expr = expressions.get(i);
                     row[i] = expr.getValue(session);
                 }
+                if (isForUpdateMvcc) {
+                    topTableFilter.lockRow();
+                }
                 result.addRow(row);
                 rowNumber++;
                 if ((sort == null || sortUsingIndex) && limitRows != 0 && result.getRowCount() >= limitRows) {
@@ -539,7 +542,8 @@ public class Select extends Query {
         }
         topTableFilter.startQuery(session);
         topTableFilter.reset();
-        topTableFilter.lock(session, isForUpdate, isForUpdate);
+        boolean exclusive = isForUpdate && !isForUpdateMvcc;
+        topTableFilter.lock(session, exclusive, exclusive);
         if (isQuickAggregateQuery) {
             queryQuick(columnCount, result);
         } else if (isGroupQuery) {
@@ -962,6 +966,9 @@ public class Select extends Query {
 
     public void setForUpdate(boolean b) {
         this.isForUpdate = b;
+        if (SysProperties.SELECT_FOR_UPDATE_MVCC && session.getDatabase().isMultiVersion()) {
+            isForUpdateMvcc = b;
+        }
     }
 
     public void mapColumns(ColumnResolver resolver, int level) {

h2/src/main/org/h2/constant/SysProperties.java

@@ -526,6 +526,12 @@ public class SysProperties {
      */
     public static boolean runFinalize = getBooleanSetting("h2.runFinalize", true);
 
+    /**
+     * System property <code>h2.selectForUpdateMvcc</code> (default: false).<br />
+     * If set, SELECT .. FOR UPDATE queries lock the rows when using MVCC.
+     */
+    public static final boolean SELECT_FOR_UPDATE_MVCC = getBooleanSetting("h2.selectForUpdateMvcc", false);
+
     /**
      * System property <code>h2.serverCachedObjects</code> (default: 64).<br />
      * TCP Server: number of cached objects per session.

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

@@ -385,7 +385,9 @@ public class RegularTable extends TableBase {
         }
         if (!force && database.isMultiVersion()) {
             // MVCC: update, delete, and insert use a shared lock.
-            // Select doesn't lock
+            // Select doesn't lock except when using FOR UPDATE and
+            // the system property h2.selectForUpdateMvcc
+            // is not enabled
             if (exclusive) {
                 exclusive = false;
             } else {

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

@@ -718,4 +718,15 @@ public class TableFilter implements ColumnResolver {
         return false;
     }
 
+    public void lockRow() {
+        if (state == FOUND) {
+            Row row = get();
+            table.removeRow(session, row);
+            table.addRow(session, row);
+            if (join != null) {
+                join.lockRow();
+            }
+        }
+    }
+
 }