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From Alex Cruikshank <a...@epitonic.com>
Subject [PATCH]: significant performance boost for JSP pages
Date Tue, 22 Feb 2000 21:14:43 GMT
I apologize in advance for the long email.

I was profiling a JSP application running on the 3.1M1 server, and I 
noticed that my JSP pages were taking much longer (by at least 2 orders of 
magnitude) than the normal servlets.  I could see that the service method 
of the JSP page was taking less than a millisecond to execute, so the bulk 
of the time must be taken up by the JSP request handling.

It turns out that the offending code is the getClassName() method in the 
org.apache.jasper.compiler.ClassName class.  This class seems to be parsing 
the actual class data to read the name of a class to get the current class 
number.  This turns out to be extraordinarily expensive; taking 10-200 
milliseconds both on our top of the line e250 SUN machine and a Compaq 
Proliant production ready Linux machine.  The time it takes to run seems to 
be dependent on the size and complexity of the JSP class.

This expense would be tolerable if the method were only called when a JSP 
file is outdated and needs to be compiled (as the author seems to have 
intended), but the current code calls the method twice every time a JSP 
page is requested regardless of whether it needs to be compiled.  What's 
worse, the code called from a synchronized method, JspLoader.loadJSP(), 
which means that every JSP page request will have wait its turn to execute 
this code.  For a moderate complexity JSP file that takes 200 milliseconds 
for the getClassName() method, this sets a hard limit of 2.5 requests per 
second for the entire server, which is unacceptable for even a relatively 
low load web site.  I observed this deadlock experimentally in my load tests.

Fortunately, this problem can be rather easily fixed without major 
architectural changes.  The problem lies in the fact that JspCompiler ends 
up calling the getClassName() method twice in its computeClassFileData() 
method and that this method is called in it's constructor.  The 
JspLoader.loadJSP() method uses an instance of JspCompiler (via the 
JspEngineContext.getCompiler() method) to determine whether a JSP file 
needs to be (re-)compiled, so it ends up executing the 
computeClassFileData() method every time, even though the data generated by 
it is used only a tiny fraction of the time.  The solution I propose 
involves spliting the code that determines whether a jsp file is outdated 
into the isOutDated() method and making it public, and moving the 
computeClassFileData() and computeJavaFileName() requests (which are needed 
for compilation) out of the constructor and into their respective accessors 
so the computation happens as needed.  This also allows us to de-couple the 
outdated test from the actual compilation, so we can synchronize only when 
the class needs to be compiled (thus avoiding deadlock with no reduction in 
safety).

A quick test on a test.jsp gave the following results (in milliseconds):
BEFORE:
[alex@duranduran tomcat]$ JspLoader.loadJSP() time: 3254
JspLoader.loadJSP() time: 77
JspLoader.loadJSP() time: 70
JspLoader.loadJSP() time: 68
JspLoader.loadJSP() time: 69
JspLoader.loadJSP() time: 111
JspLoader.loadJSP() time: 94
JspLoader.loadJSP() time: 68
JspLoader.loadJSP() time: 68
...
JspLoader.loadJSP() time: 69
JspLoader.loadJSP() time: 68
[alex@duranduran tomcat]$ touch webpages/test.jsp
[alex@duranduran tomcat]$ JspLoader.loadJSP() time: 854
JspLoader.loadJSP() time: 130
JspLoader.loadJSP() time: 70
JspLoader.loadJSP() time: 68
JspLoader.loadJSP() time: 68
JspLoader.loadJSP() time: 68
...
JspLoader.loadJSP() time: 68
JspLoader.loadJSP() time: 69

AFTER:
JspLoader.loadJSP() time: 2950
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 2
touch webpages/test.jsp
[alex@duranduran tomcat]$ JspLoader.loadJSP() time: 1562
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 14
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1
JspLoader.loadJSP() time: 1

And the difference would be greater for a more complicated JSP file.  I've 
also seen the elimination of deadlock with these changes in my load tests, 
but reproducing those for you would be too complicated.

These changes are basically a work around to a more fundamental problems 
that the JspCompilation system hasn't been designed for performance, and 
the Mangling scheme is clunky.  IMHO, these things should be overhauled for 
RC2 (as is stated more than once in the existing code comments).  I've 
tried to keep these changes minimal to keep the 3.1 server stable.

The following diffs are against the TOMCAT_31_M1_RC1 version of tomcat in CVS:

T_31_M1_RC1 JspLoader.java
cvs diff: warning: unrecognized response `cvs: setgroups: Operation not 
permitted' from cvs server
Index: JspLoader.java
===================================================================
RCS file: 
/home/cvspublic/jakarta-tomcat/src/share/org/apache/jasper/runtime/JspLoader 
.java,v
retrieving revision 1.3
diff -u -r1.3 JspLoader.java
--- JspLoader.java      1999/12/21 12:34:31     1.3
+++ JspLoader.java      2000/02/22 20:03:18
@@ -1,5 +1,5 @@
  /*
- * $Header: 
/home/cvspublic/jakarta-tomcat/src/share/org/apache/jasper/runtime/JspLoader 
.java,v 1.3 1
999/12/21 12:34:31 rubys Exp $
+ * $Header: 
/home/cvs/jakarta-tomcat/src/share/org/apache/jasper/runtime/JspLoader.java, 
v 1.3 1999/12
/21 12:34:31 rubys Exp $
   * $Revision: 1.3 $
   * $Date: 1999/12/21 12:34:31 $
   *
@@ -207,10 +207,11 @@
       *  @param classpath explicitly set the JSP compilation path.
       *  @return true if JSP files is newer
       */
-    public synchronized boolean loadJSP(String name, String classpath,
+    public boolean loadJSP(String name, String classpath,
         boolean isErrorPage, HttpServletRequest req, HttpServletResponse res)
         throws JasperException, FileNotFoundException
      {
+long loadJSPTime = System.currentTimeMillis();
         Class jspClass = (Class) loadedJSPs.get(name);
         boolean firstTime = jspClass == null;

@@ -223,7 +224,14 @@
          Compiler compiler = ctxt.createCompiler();

          try {
-            outDated = compiler.compile();
+            if ((jspClass == null) || (compiler.isOutDated() ))
+            {
+                synchronized ( this )
+                {
+                    if ((jspClass == null) || (compiler.isOutDated() ))
+                        outDated = compiler.compile();
+                }
+            }
          } catch (FileNotFoundException ex) {
              throw ex;
          } catch (JasperException ex) {
@@ -244,6 +252,7 @@
             loadedJSPs.put(name, jspClass);
         }

+System.err.println( "JspLoader.loadJSP() time: " + 
(System.currentTimeMillis() - loadJSPTime) );
         return outDated;
      }


AT_31_M1_RC1 Compiler.java
cvs diff: warning: unrecognized response `cvs: setgroups: Operation not 
permitted' from cvs server
Index: Compiler.java
===================================================================
RCS file: 
/home/cvspublic/jakarta-tomcat/src/share/org/apache/jasper/compiler/Compiler 
.java,v
retrieving revision 1.6
diff -u -r1.6 Compiler.java
--- Compiler.java       2000/01/08 21:31:38     1.6
+++ Compiler.java       2000/02/22 20:03:31
@@ -1,7 +1,7 @@
  /*
- * $Header: 
/home/cvspublic/jakarta-tomcat/src/share/org/apache/jasper/compiler/Compiler 
.java,v 1.6 2
000/01/08 21:31:38 rubys Exp $
- * $Revision: 1.6 $
- * $Date: 2000/01/08 21:31:38 $
+ * $Header: 
/home/cvs/jakarta-tomcat/src/share/org/apache/jasper/compiler/Compiler.java, 
v 1.7 2000/01
/21 04:17:21 rubys Exp $
+ * $Revision: 1.7 $
+ * $Date: 2000/01/21 04:17:21 $
   *
   * ====================================================================
   *
@@ -230,7 +230,7 @@
       * subclasses of Compiler. This is used by the compile method
       * to do all the compilation.
       */
-    protected abstract boolean isOutDated();
+    public abstract boolean isOutDated();

      /**
       * Set java compiler info


cvs diff: warning: unrecognized response `cvs: setgroups: Operation not 
permitted' from cvs server
Index: JspCompiler.java
===================================================================
RCS file: 
/home/cvspublic/jakarta-tomcat/src/share/org/apache/jasper/compiler/JspCompi 
ler.java,v
retrieving revision 1.4
diff -u -r1.4 JspCompiler.java
--- JspCompiler.java    1999/12/28 16:25:54     1.4
+++ JspCompiler.java    2000/02/22 20:03:40
@@ -90,8 +90,8 @@
          setMangler(this);
          computePackageName();
          computeClassFileName();
-        computeClassFileData();
-        computeJavaFileName();
+ //       computeClassFileData();
+ //       computeJavaFileName();
      }

      public final String getPackageName() {
@@ -99,10 +99,18 @@
      }

      public final String getClassName() {
+        if ( className == null )
+        {
+            computeClassFileData();
+        }
          return className;
      }

      public final String getJavaFileName() {
+        if ( javaFileName == null )
+        {
+            computeJavaFileName();
+        }
          return javaFileName;
      }

@@ -111,16 +119,6 @@
      }


-    /**
-     * Return true if the .class file is outdated w.r.t
-     * the JSP file.
-     *
-     * Can (meant to) be overridden by subclasses of JspCompiler.
-     */
-    protected boolean isOutDated() {
-        return outDated;
-    }
-
      public static String [] keywords = {
          "abstract", "boolean", "break", "byte",
          "case", "catch", "char", "class",
@@ -184,7 +182,7 @@
      }

      public final void computeJavaFileName() {
-       javaFileName = className + ".java";
+       javaFileName = getClassName() + ".java";
         if (outputDir != null && !outputDir.equals(""))
             javaFileName = outputDir + File.separatorChar + javaFileName;
      }
@@ -251,8 +249,33 @@
      }


+    /**
+     * Determines whether the current JSP class is older than the JSP file 
from whence it came
+     */
+    public boolean isOutDated()
+    {
+        ServletContext ctx = ctxt.getServletContext();
+        File jspReal = null;
+
+        if (ctx != null)
+            jspReal = new File(ctx.getRealPath(jsp.getPath()));
+        else
+            jspReal = jsp;
+
+        File classFile = new File(classFileName);
+        if (classFile.exists())
+        {
+            outDated = classFile.lastModified() < jspReal.lastModified();
+        }
+        else
+        {
+            outDated = true;
+        }
+        return outDated;
+    }
+
      private final void computeClassFileData()
-       throws JasperException
+//     throws JasperException
      {
          ServletContext ctx = ctxt.getServletContext();

@@ -278,14 +301,21 @@
             } else {
                 cfd = new ClassFileData(outDated, classFileName, null);
             }
-            String classNameFromFile = ClassName.getClassName(classFileName);
-            String cn = cfd.getClassName();
-            int lastDot = cn.lastIndexOf('.');
-            if (lastDot != -1)
-                className = cn.substring(lastDot+1,
-                                         classNameFromFile.length());
-            else
-                className = cn;
+            try
+            {
+                String classNameFromFile = 
ClassName.getClassName(classFileName);
+                String cn = cfd.getClassName();
+                int lastDot = cn.lastIndexOf('.');
+                if (lastDot != -1)
+                    className = cn.substring(lastDot+1,
+                                             classNameFromFile.length());
+                else
+                    className = cn;
+            }
+            catch (JasperException ex)
+            {
+                ex.printStackTrace();
+            }
          }
      }
  }
@@ -317,10 +347,6 @@
              = 
Integer.valueOf(className.substring(className.lastIndexOf(Constants.JSP_TOKEN)+
                                                    Constants.JSP_TOKEN.leng 
Constants.JSP_TOKEN.length(),
                                                    className.length())).int 
className.length())).intValue();
-    }
-
-    public boolean isOutDated() {
-        return outDated;
      }

      public String getClassName() {



--------------------------
Alex Cruikshank
Senior Software Engineer
Epitonic.com

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