JDBC-464 Expose close() method on dbmd, add entry to release notes

src/documentation/release_notes.md

@@ -238,6 +238,10 @@ The following has been changed or fixed since Jaybird 3.0.0-beta-1
 -   Changed logging of Embedded library to only log on error if none of the
     libraries could be loaded.
 -   Fixed: native protocol is 20x-30x slower than Jaybird 2.2 native [JDBC-463](http://tracker.firebirdsql.org/browse/JDBC-463)
+-   Fixed: `ResultSetMetaData.getPrecision` of a numeric column when no 
+    transaction is active throws an SQLException ([JDBC-464](http://tracker.firebirdsql.org/browse/JDBC-464))\
+    As part of this fix, the handling of queries executed by `FBDatabaseMetaData` 
+    has been changed. Most metadata queries are now kept prepared for reuse.
 
 What's new in Jaybird 3.0
 =========================

src/main/org/firebirdsql/jdbc/FBDatabaseMetaData.java

@@ -147,13 +147,16 @@ protected FBDatabaseMetaData(FBConnection c) throws SQLException {
         firebirdSupportInfo = supportInfoFor(c);
     }
 
-    protected void close() {
+    @Override
+    public void close() {
         try {
-            for (FBStatement stmt : statements.values()) {
-                stmt.close();
+            for (FBStatement stmt : new ArrayList<>(statements.values())) {
+                try {
+                    stmt.close();
+                } catch (SQLException e) {
+                   log.warn("error in DatabaseMetaData.close", e);
+                }
             }
-        } catch (SQLException e) {
-           log.warn("error in DatabaseMetaData.close", e);
         } finally {
             statements.clear();
         }

src/main/org/firebirdsql/jdbc/FirebirdDatabaseMetaData.java

@@ -34,6 +34,7 @@
  * 
  * @author <a href="mailto:[email protected]">Michael Romankiewicz</a>
  */
+@SuppressWarnings("unused")
 public interface FirebirdDatabaseMetaData extends DatabaseMetaData {
 
     /**
@@ -105,4 +106,12 @@ public interface FirebirdDatabaseMetaData extends DatabaseMetaData {
      * @see #getDatabaseDialect()
      */
     int getConnectionDialect() throws SQLException;
+
+    /**
+     * Closes any cached metadata statements held by this database metadata implementation.
+     * <p>
+     * The database metadata object itself remains usable. Exceptions during statement close are logged and suppressed.
+     * </p>
+     */
+    void close();
 }