DZone Snippets: performance code

Speeding up Java I/O - Read method

rick (Rick Ross) — Sat, 17 May 2008 14:49:13 GMT

The following example counts the number of newline bytes ('\n') in a file. It simply uses the read method on a FileInputStream:



 import java.io.*;

  

  public class intro1 {

    public static void main(String args[]) {

      if (args.length != 1) {

        System.err.println("missing filename");

        System.exit(1);

      }

      try {

        FileInputStream fis =

            new FileInputStream(args[0]);

        int cnt = 0;

        int b;

        while ((b = fis.read()) != -1) {

          if (b == '\n')

            cnt++;

        }

        fis.close();

        System.out.println(cnt);

      }

      catch (IOException e) {

        System.err.println(e);

      }

    }

  }

Subject to Sun's Code Sample License

FInd slow actions in a Rails app

sikelianos (Zeke Sikelianos) — Tue, 21 Aug 2007 21:08:20 GMT



# Show a list of actions sorted by time taken. Useful for finding slow actions.

cat log/development.log | awk '/Completed/ { print "[" $3 "] - " $0 }' | sort -nr

StopWatch - Why is my app so slow ???

nivek (Kevin Gaudin) — Wed, 07 Feb 2007 21:51:22 GMT

StopWatch is a small class allowing to manage multiple concurrent stopwatches to measure time elapsed between two calls. Nothing is done while time is rolling (no thread, no loop), it only stores and compares timestamps.



import java.util.Hashtable;



public class StopWatch {

    private static final Hashtable startTime = new Hashtable();

    

    public static void start(String id){

        startTime.put(id,new Long(System.currentTimeMillis()));

    }



    public static long stop(String id){

        return System.currentTimeMillis() - ((Long)startTime.remove(id)).longValue();

    }

}

Example of use :



public main(String[] args) {

    // Start a global stopwatch

    StopWatch.start("GLOBAL");



    // evaluate time used by task 1

    StopWatch.start("TASK1");

    executeTask1();

    System.out.println("Time elapsed for task 1 : " + StopWatch.stop("TASK1") + "ms";



    // evaluate time used by task 2

    StopWatch.start("TASK2");

    executeTask2();

    System.out.println("Time elapsed for task 2 : " + StopWatch.stop("TASK2") + "ms";



    // Display time elapsed for full processing

    System.out.println("Total processing time : " + StopWatch.stop("GLOBAL") + "ms";

}

Switch Oracle CLOB to VARCHAR2

dcmanges (Dan Manges) — Mon, 20 Nov 2006 08:23:21 GMT

This rake task creates a database script to change all Oracle CLOB columns to VARCHAR2 columns.

Changing Oracle CLOBs to VARCHAR2s can result in a huge performance increase, especially if the database and app servers are not close together on the network.



namespace :db do

  task :fix_clobs => [:environment] do |t|

    @outfile = File.expand_path(File.join(RAILS_ROOT,"db","fix_clobs.sql"))

  

    File.open(@outfile, "w") do |file|

      ActiveRecord::Base.connection.tables.each do |table_name|

        begin

          model = eval(table_name.classify)

          model.columns.each do |column|

            if column.sql_type == "CLOB"

              file.write("ALTER TABLE #{table_name} ADD #{column.name}_temp VARCHAR2(4000);\n")

              file.write("UPDATE #{table_name} SET #{column.name}_temp = #{column.name};\n")

              file.write("COMMIT;\n")

              file.write("ALTER TABLE #{table_name} DROP COLUMN #{column.name};\n")

              file.write("ALTER TABLE #{table_name} RENAME COLUMN #{column.name}_temp TO #{column.name};\n")

              file.write("\n")

            end

          end

         rescue => ex

           puts "Failed for #{table_name} with #{ex.class}"

         end

      end

    end

  end

end

High-performance Ruby: faster Symbol.to_s

ciconia (Sharon Rosner) — Tue, 15 Aug 2006 11:22:50 GMT

Here's something that I found useful for shaving a few microseconds off. The performance gain ranges between 10% and 35%! YMMV.

Note: updated with suggestion by trans.



class Symbol

  def to_s

    @str_rep || (@str_rep = id2name.freeze)

  end

end

Analyse a MySQL Table for Inefficiencies

offspinner () — Thu, 09 Feb 2006 22:56:32 GMT

// description of your code here



SELECT * FROM tags PROCEDURE ANALYSE()

Analyse a MySQL Query for inefficiencies

offspinner () — Thu, 09 Feb 2006 22:40:35 GMT

// description of your code here



EXPLAIN SELECT t2.dbid, t2.tag, COUNT(t2.dbid) * 20 AS match_count

FROM tags AS t1, tags AS t2

WHERE t1.dbid = '105318'

AND t2.tag = t1.tag

AND t1.dbid != t2.dbid

GROUP BY t2.dbid

ORDER BY match_count;

Setup for Performance Testing: Clear cache, buffers (MSSQL)

MattScilipoti (Matt Scilipoti) — Thu, 08 Dec 2005 03:33:32 GMT

For Microsoft SQL (MSSQL).
Use this to clear the cache and buffers to ensure comparison are accurate.



dbcc freeproccache

go

dbcc dropcleanbuffers

go