svn commit: r707097 - in /db/derby/code/trunk/java/engine/org/apache/derby/impl: jdbc/LOBStoredProcedure.java sql/catalog/DataDictionaryImpl.java

[kr...@apache.org]

Author: kristwaa
Date: Wed Oct 22 08:18:08 2008
New Revision: 707097

URL: http://svn.apache.org/viewvc?rev=707097&view=rev
Log:
DERBY-3769: Make LOBStoredProcedure on the server side smarter about the read buffer size.
Adjusts the maximum return size in characters for the CLOB stored procedure to 10890 (DB2_VARCHAR_MAXWIDTH / 3). This potentially results in anything from 10890 to 10890*3 bytes to be returned to the client in one round-trip, depending on the bytes per char ratio (determined by the modified UTF8 encoding).
This fix is sub-optimal for Clobs with ASCII contents, but improves performance for Clobs with contents requiring 2 or 3 bytes per char dramatically.
Patch file: derby-3769-2b-clob_buffer_size_adjustment.diff

Modified:
    db/derby/code/trunk/java/engine/org/apache/derby/impl/jdbc/LOBStoredProcedure.java
    db/derby/code/trunk/java/engine/org/apache/derby/impl/sql/catalog/DataDictionaryImpl.java

Modified: db/derby/code/trunk/java/engine/org/apache/derby/impl/jdbc/LOBStoredProcedure.java
URL: http://svn.apache.org/viewvc/db/derby/code/trunk/java/engine/org/apache/derby/impl/jdbc/LOBStoredProcedure.java?rev=707097&r1=707096&r2=707097&view=diff
==============================================================================
--- db/derby/code/trunk/java/engine/org/apache/derby/impl/jdbc/LOBStoredProcedure.java (original)
+++ db/derby/code/trunk/java/engine/org/apache/derby/impl/jdbc/LOBStoredProcedure.java Wed Oct 22 08:18:08 2008
@@ -37,13 +37,28 @@
 public class LOBStoredProcedure {
 
     /**
-     * The maximum length of the data returned from the LOB stored procedures.
+     * The maximum length of the data returned from the BLOB stored procedures.
      * <p>
      * This value is currently dictated by the maximum length of
      * VARCHAR/VARBINARY, because these are the return types of the stored
      * procedures.
      */
-    public static final int MAX_RETURN_LENGTH = Limits.DB2_VARCHAR_MAXWIDTH;
+    public static final int MAX_BLOB_RETURN_LEN = Limits.DB2_VARCHAR_MAXWIDTH;
+
+    /**
+     * The maximum length of the data returned from the CLOB stored procedures.
+     * <p>
+     * This value is currently dictated by the maximum length of
+     * VARCHAR/VARBINARY, because these are the return types of the stored
+     * procedures, and the modified UTF8 encoding used for CLOB data. This
+     * threshold value could be higher (equal to {@code MAX_BLOB_RETURN_LEN}),
+     * but then the procedure fetching data from the CLOB must be rewritten to
+     * have more logic.
+     * <p>
+     * For now we use the defensive assumption that all characters are
+     * represented by three bytes.
+     */
+    public static final int MAX_CLOB_RETURN_LEN = MAX_BLOB_RETURN_LEN / 3;
 
     /**
      * Creates a new empty Clob and registers it in the HashMap in the
@@ -148,7 +163,7 @@
      *            the substring begins.
      * @param len an integer representing the maximum length of the substring.
      *      The value will be reduced to the maximum allowed return length if
-     *      required (see {@link #MAX_RETURN_LENGTH}).
+     *      required (see {@link #MAX_CLOB_RETURN_LEN}).
      * @return A substring from the {@code Clob} starting at the given position,
      *      not longer than {@code len} characters.
      * @throws SQLException
@@ -157,7 +172,7 @@
         long pos, int len) throws SQLException {
         // Don't read more than what we can represent as a VARCHAR.
         // See DERBY-3769.
-        len = Math.min(len, MAX_RETURN_LENGTH);
+        len = Math.min(len, MAX_CLOB_RETURN_LEN);
         return getClobObjectCorrespondingtoLOCATOR(LOCATOR).getSubString(pos, len);
     }
 
@@ -303,7 +318,7 @@
      *                needs to be retrieved.
      * @param len the maximum number of bytes to read. The value will be
      *      reduced to the maximum allowed return length if required
-     *      (see {@link #MAX_RETURN_LENGTH}).
+     *      (see {@link #MAX_BLOB_RETURN_LEN}).
      * @param pos the position from which the bytes from the Blob need to be
      *            retrieved.
      * @return A byte array containing the bytes read, starting from position
@@ -315,7 +330,7 @@
     throws SQLException {
         // Don't read more than what we can represent as a VARBINARY.
         // See DERBY-3769.
-        len = Math.min(len, MAX_RETURN_LENGTH);
+        len = Math.min(len, MAX_BLOB_RETURN_LEN);
         return getBlobObjectCorrespondingtoLOCATOR(LOCATOR).getBytes(pos, len);
     }
 

Modified: db/derby/code/trunk/java/engine/org/apache/derby/impl/sql/catalog/DataDictionaryImpl.java
URL: http://svn.apache.org/viewvc/db/derby/code/trunk/java/engine/org/apache/derby/impl/sql/catalog/DataDictionaryImpl.java?rev=707097&r1=707096&r2=707097&view=diff
==============================================================================
--- db/derby/code/trunk/java/engine/org/apache/derby/impl/sql/catalog/DataDictionaryImpl.java (original)
+++ db/derby/code/trunk/java/engine/org/apache/derby/impl/sql/catalog/DataDictionaryImpl.java Wed Oct 22 08:18:08 2008
@@ -11078,7 +11078,7 @@
                 false,
                 DataTypeDescriptor.getCatalogType(
                     Types.VARCHAR,
-                    LOBStoredProcedure.MAX_RETURN_LENGTH),
+                    LOBStoredProcedure.MAX_CLOB_RETURN_LEN),
                 tc,
                 "org.apache.derby.impl.jdbc.LOBStoredProcedure");
         }
@@ -11266,7 +11266,7 @@
                 false,
                 DataTypeDescriptor.getCatalogType(
                     Types.VARBINARY,
-                    LOBStoredProcedure.MAX_RETURN_LENGTH),
+                    LOBStoredProcedure.MAX_BLOB_RETURN_LEN),
                 tc,
                 "org.apache.derby.impl.jdbc.LOBStoredProcedure");
         }