Require a distinction to be made between read-only and read-write queries so

that we can route read-only queries to one or more read-only mirrors of a
database (the MySQL database drivers supports round-robin load balancing of
queries to read-only slaves).


git-svn-id: https://samskivert.googlecode.com/svn/trunk@1822 6335cc39-0255-0410-8fd6-9bcaacd3b74c

src/java/com/samskivert/jdbc/ConnectionProvider.java

@@ -48,6 +48,8 @@ public interface ConnectionProvider
      * connection when it is released if appropriate.
      *
      * @param ident the database connection identifier.
+     * @param readOnly whether or not the connection may be to a read-only
+     * mirror of the repository.
      *
      * @return an active JDBC connection (which may have come from a
      * connection pool).
@@ -55,7 +57,7 @@ public interface ConnectionProvider
      * @exception PersistenceException thrown if a problem occurs trying
      * to open the requested connection.
      */
-    public Connection getConnection (String ident)
+    public Connection getConnection (String ident, boolean readOnly)
         throws PersistenceException;
 
     /**
@@ -64,10 +66,13 @@ public interface ConnectionProvider
      *
      * @param ident the database identifier used when obtaining this
      * connection.
+     * @param readOnly the same value that was passed to {@link #getConnection}
+     * to obtain this connection.
      * @param conn the connection to release (back into the pool or to be
      * closed if pooling is not going on).
      */
-    public void releaseConnection (String ident, Connection conn);
+    public void releaseConnection (String ident, boolean readOnly,
+                                   Connection conn);
 
     /**
      * Called by the repository if a failure occurred on the connection.
@@ -77,10 +82,12 @@ public interface ConnectionProvider
      *
      * @param ident the database identifier used when obtaining this
      * connection.
+     * @param readOnly the same value that was passed to {@link #getConnection}
+     * to obtain this connection.
      * @param conn the connection that failed.
      * @param error the error thrown by the connection (which may be used
      * to determine if the connection should be closed or can be reused).
      */
-    public void connectionFailed (String ident, Connection conn,
+    public void connectionFailed (String ident, boolean readOnly,
-                                  SQLException error);
+                                  Connection conn, SQLException error);
 }

src/java/com/samskivert/jdbc/JORARepository.java

@@ -62,7 +62,7 @@ public abstract class JORARepository extends SimpleRepository
     protected <T> int insert (final Table<T> table, final T object)
         throws PersistenceException
     {
-        return execute(new Operation<Integer>() {
+        return executeUpdate(new Operation<Integer>() {
             public Integer invoke (Connection conn, DatabaseLiaison liaison)
                 throws SQLException, PersistenceException
             {
@@ -79,7 +79,7 @@ public abstract class JORARepository extends SimpleRepository
     protected <T> void update (final Table<T> table, final T object)
         throws PersistenceException
     {
-        execute(new Operation<Object>() {
+        executeUpdate(new Operation<Object>() {
             public Object invoke (Connection conn, DatabaseLiaison liaison)
                 throws SQLException, PersistenceException
             {
@@ -188,7 +188,7 @@ public abstract class JORARepository extends SimpleRepository
     protected <T> int store (final Table<T> table, final T object)
         throws PersistenceException
     {
-        return execute(new Operation<Integer>() {
+        return executeUpdate(new Operation<Integer>() {
             public Integer invoke (Connection conn, DatabaseLiaison liaison)
                 throws SQLException, PersistenceException
             {
@@ -211,7 +211,7 @@ public abstract class JORARepository extends SimpleRepository
     {
         final FieldMask mask = table.getFieldMask();
         mask.setModified(field);
-        execute(new Operation<Object>() {
+        executeUpdate(new Operation<Object>() {
             public Object invoke (Connection conn, DatabaseLiaison liaison)
                 throws SQLException, PersistenceException
             {
@@ -233,7 +233,7 @@ public abstract class JORARepository extends SimpleRepository
         for (int ii = 0; ii < fields.length; ii++) {
             mask.setModified(fields[ii]);
         }
-        execute(new Operation<Object>() {
+        executeUpdate(new Operation<Object>() {
             public Object invoke (Connection conn, DatabaseLiaison liaison)
                 throws SQLException, PersistenceException
             {
@@ -246,7 +246,7 @@ public abstract class JORARepository extends SimpleRepository
     protected <T> void delete (final Table<T> table, final T object)
         throws PersistenceException
     {
-        execute(new Operation<Object>() {
+        executeUpdate(new Operation<Object>() {
             public Object invoke (Connection conn, DatabaseLiaison liaison)
                 throws SQLException, PersistenceException
             {

src/java/com/samskivert/jdbc/SimpleRepository.java

@@ -70,7 +70,7 @@ public class SimpleRepository extends Repository
         // give the repository a chance to do any schema migration before
         // things get further underway
         try {
-            execute(new Operation<Object>() {
+            executeUpdate(new Operation<Object>() {
                 public Object invoke (Connection conn, DatabaseLiaison liaison)
                     throws SQLException, PersistenceException
                 {
@@ -85,7 +85,7 @@ public class SimpleRepository extends Repository
     }
 
     /**
-     * Executes the supplied operation. In the event of a transient
+     * Executes the supplied read-only operation. In the event of a transient
      * failure, the repository will attempt to reestablish the database
      * connection and try the operation again.
      *
@@ -94,7 +94,20 @@ public class SimpleRepository extends Repository
     protected <V> V execute (Operation<V> op)
 	throws PersistenceException
     {
-        return execute(op, true);
+        return execute(op, true, true);
+    }
+
+    /**
+     * Executes the supplied read-write operation. In the event of a transient
+     * failure, the repository will attempt to reestablish the database
+     * connection and try the operation again.
+     *
+     * @return whatever value is returned by the invoked operation.
+     */
+    protected <V> V executeUpdate (Operation<V> op)
+	throws PersistenceException
+    {
+        return execute(op, true, false);
     }
 
     /**
@@ -104,14 +117,16 @@ public class SimpleRepository extends Repository
      * case a call to <code>rollback()</code> is executed on the
      * connection.
      *
-     * @param retryOnTransientFailure if true and the operation fails due
+     * @param retryOnTransientFailure if true and the operation fails due to a
-     * to a transient failure (like losing the connection to the database
+     * transient failure (like losing the connection to the database or
-     * or deadlock detection), the connection to the database will be
+     * deadlock detection), the connection to the database will be
      * reestablished (if necessary) and the operation attempted once more.
+     * @param readOnly whether or not to request a read-only connection.
      *
      * @return whatever value is returned by the invoked operation.
      */
-    protected <V> V execute (Operation<V> op, boolean retryOnTransientFailure)
+    protected <V> V execute (Operation<V> op, boolean retryOnTransientFailure,
+                             boolean readOnly)
 	throws PersistenceException
     {
         Connection conn = null;
@@ -129,7 +144,7 @@ public class SimpleRepository extends Repository
 
         try {
             // obtain our database connection and associated goodies
-            conn = _provider.getConnection(_dbident);
+            conn = _provider.getConnection(_dbident, readOnly);
             liaison = LiaisonRegistry.getLiaison(conn);
 
             // find out if we support transactions
@@ -172,7 +187,7 @@ public class SimpleRepository extends Repository
 
             if (conn != null) {
                 // let the connection provider know that the connection failed
-                _provider.connectionFailed(_dbident, conn, sqe);
+                _provider.connectionFailed(_dbident, readOnly, conn, sqe);
 
                 // clear out the reference so that we don't release it later
                 conn = null;
@@ -189,7 +204,7 @@ public class SimpleRepository extends Repository
                 String msg = StringUtil.split("" + sqe, "\n")[0];
                 Log.info("Transient failure executing operation, " +
                          "retrying [error=" + msg + "].");
-                return execute(op, false);
+                return execute(op, false, readOnly);
             }
 
             String err = "Operation invocation failed";
@@ -222,7 +237,7 @@ public class SimpleRepository extends Repository
         } finally {
             if (conn != null) {
                 // release the database connection
-                _provider.releaseConnection(_dbident, conn);
+                _provider.releaseConnection(_dbident, readOnly, conn);
             }
 	}
     }
@@ -234,7 +249,7 @@ public class SimpleRepository extends Repository
     protected int update (final String query)
         throws PersistenceException
     {
-        return execute(new Operation<Integer>() {
+        return executeUpdate(new Operation<Integer>() {
             public Integer invoke (Connection conn, DatabaseLiaison liaison)
                 throws SQLException, PersistenceException
             {
@@ -257,7 +272,7 @@ public class SimpleRepository extends Repository
     protected void checkedUpdate (final String query, final int count)
         throws PersistenceException
     {
-        execute(new Operation<Object>() {
+        executeUpdate(new Operation<Object>() {
             public Object invoke (Connection conn, DatabaseLiaison liaison)
                 throws SQLException, PersistenceException
             {
@@ -287,7 +302,7 @@ public class SimpleRepository extends Repository
     protected void maintenance (final String action, final String table)
         throws PersistenceException
     {
-        execute(new Operation<Object>() {
+        executeUpdate(new Operation<Object>() {
             public Object invoke (Connection conn, DatabaseLiaison liaison)
                 throws SQLException, PersistenceException
             {

src/java/com/samskivert/jdbc/StaticConnectionProvider.java

@@ -127,13 +127,15 @@ public class StaticConnectionProvider implements ConnectionProvider
     }
 
     // documentation inherited
-    public Connection getConnection (String ident)
+    public Connection getConnection (String ident, boolean readOnly)
         throws PersistenceException
     {
-        Mapping conmap = _idents.get(ident);
+        String mapkey = ident + ":" + readOnly;
+        Mapping conmap = _idents.get(mapkey);
 
         // open the connection if we haven't already
         if (conmap == null) {
+            String[] defaults;
             Properties props =
                 PropertiesUtil.getSubProperties(_props, ident, DEFAULTS_KEY);
 
@@ -147,9 +149,11 @@ public class StaticConnectionProvider implements ConnectionProvider
             err = "No driver password specified [ident=" + ident + "].";
             String password = requireProp(props, "password", err);
 
-            // we cache connections by username+url to avoid making more
+            // if this is a read-only connection,
-            // that one connection to a particular database server
+
-            String key = username + "@" + url;
+            // we cache connections by username+url+readOnly to avoid making
+            // more that one connection to a particular database server
+            String key = username + "@" + url + ":" + readOnly;
             conmap = _keys.get(key);
             if (conmap == null) {
                 Log.debug("Creating " + key + " for " + ident + ".");
@@ -157,42 +161,53 @@ public class StaticConnectionProvider implements ConnectionProvider
                 conmap.key = key;
                 conmap.connection =
                     openConnection(driver, url, username, password);
+
+                // make the connection read-only to let the JDBC driver know
+                // that it can and should use the read-only mirror(s)
+                if (readOnly) {
+                    try {
+                        conmap.connection.setReadOnly(true);
+                    } catch (SQLException sqe) {
+                        closeConnection(ident, conmap.connection);
+                        err = "Failed to make connection read-only " +
+                            "[key=" + key + ", ident=" + ident + "].";
+                        throw new PersistenceException(err, sqe);
+                    }
+                }
+
                 _keys.put(key, conmap);
             } else {
                 Log.debug("Reusing " + key + " for " + ident + ".");
             }
 
             // cache the connection
-            conmap.idents.add(ident);
+            conmap.idents.add(mapkey);
-            _idents.put(ident, conmap);
+            _idents.put(mapkey, conmap);
         }
 
         return conmap.connection;
     }
 
     // documentation inherited
-    public void releaseConnection (String ident, Connection conn)
+    public void releaseConnection (String ident, boolean readOnly,
+                                   Connection conn)
     {
         // nothing to do here, all is well
     }
 
     // documentation inherited
-    public void connectionFailed (String ident, Connection conn,
+    public void connectionFailed (String ident, boolean readOnly,
-                                  SQLException error)
+                                  Connection conn, SQLException error)
     {
-        Mapping conmap = _idents.get(ident);
+        String mapkey = ident + ":" + readOnly;
+        Mapping conmap = _idents.get(mapkey);
         if (conmap == null) {
             Log.warning("Unknown connection failed!? [ident=" + ident + "].");
             return;
         }
 
         // attempt to close the connection
-        try {
+        closeConnection(ident, conmap.connection);
-            conmap.connection.close();
-        } catch (SQLException sqe) {
-            Log.warning("Error closing failed connection [ident=" + ident +
-                        ", error=" + sqe + "].");
-        }
 
         // clear it from our mapping tables
         for (int ii = 0; ii < conmap.idents.size(); ii++) {
@@ -224,6 +239,16 @@ public class StaticConnectionProvider implements ConnectionProvider
         }
     }
 
+    protected void closeConnection (String ident, Connection conn)
+    {
+        try {
+            conn.close();
+        } catch (SQLException sqe) {
+            Log.warning("Error closing failed connection [ident=" + ident +
+                        ", error=" + sqe + "].");
+        }
+    }
+
     protected static String requireProp (
         Properties props, String name, String errmsg)
 	throws PersistenceException