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Oracle Delete Taking a Long Time

Tim — Sun, 17 Jan 2010 02:16:15 +0000

It may look like your delete statement is hung, but ff your table has foreign keys in another table without indexes on that column Oracle will full table scan that other table for every row that you’re deleting. Hopefully this saves someone some time.

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Luhn Digit Generation Oracle PL/SQL Implementation

Tim — Tue, 06 Oct 2009 11:27:06 +0000

Here's how to generate a Luhn Mod-10 Check Digit. It's implemented as a function in oracle PL/SQL. I spent 2 hours looking for this online, then decided to implement it myself since it's not that hard. Anyway, I thought I'd post it here for the next person trolling google for it. This is useful for generating credit card numbers or any other place you need a check digit.

This algorithm works by doing the same thing as the validation algorithm, but shifted over one character (the equivalent of adding a zero to a number, generating the sum & subtracting 10).

*EDIT - there was a bug in this code, i just fixed it on 12/4/2009, the old code returned 10 instead of zero. It also was only working on even numbers, sorry about that!

CREATE OR REPLACE FUNCTION generate_luhn (togen IN varchar)
RETURN number
IS
curval NUMBER := 0;
total NUMBER := 0;
everyother NUMBER := 1;

BEGIN
IF(
togen IS NULL
) then
RETURN 0;
end IF;

FOR i IN reverse 1 .. LENGTH(togen) loop
curval:=SUBSTR(togen, i, 1);
IF everyother = 1 then
everyother := 0;
curval := curval * 2;
IF(curval> 9) then
curval:=curval-9;
end IF;
else
everyother := 1;
end IF;

total := total + curval;
end loop;
IF MOD(total, 10) = 0 THEN
RETURN 0;
ELSE
RETURN 10 - MOD(total, 10);
END IF;
END generate_luhn;
/

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Capturing Uncaught Java Exceptions in a Bash Shell Script

Tim — Wed, 13 May 2009 16:53:28 +0000

I was burned one to many times by chaining dependent java programs together in a bash script.

By default the java executable will return zero if the program exited manually, and 1 if there was an uncaught RuntimeException.

Let's say test.sh runs a java program, we want to run it 3 times, but if it fails during any of the runs we want to abort our run.

#!/usr/bin/bash
java Test
exitval=$?
echo "exit val: ${exitval}"
exit $exitval

Then in our shell script to run test.sh each time we'd do something like this.

#!/usr/bin/bash

./test.sh
step1=$?

if [ $step1 -eq "0" ] ; then
./test.sh
step2=$?
if [ $step2 -eq "0" ] ; then
./test.sh
step3=$?
if [ $step3 -eq "0" ] ; then
echo "Finished successfully."
else
echo "Step 3 failed."
fi
else
echo "Step 2 failed with ${step2}"
fi
else
echo "Step 1 Failed. with ${step1}"
fi

To test my script I made a little java class that will error out half the time that looks like this:

import java.util.Random;
public class Test
{

public static void main(String[] args)
{
Random gen = new Random();
if(gen.nextInt(2)> 0)
{
System.out.println("I Win!");
}
else
{
throw new RuntimeException("I Fail!");
}
}
}

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Mylyn + Trac + wsgi

Tim — Thu, 19 Feb 2009 13:16:22 +0000

I am using mod_wsgi instead of mod_python for my trac .11 install.

I'm also using the AccountManager plugin for authentication, and don't have anonymous access setup.

Anyway, authentication wasn't working (through XML RPC) hence mylyn didn't have the perms to do anything, and was silently defaulting to anon mode. even though I had the XML RPC plugin installed and permissions set up.

Here's the steps to get them all playing nice (this was harder than it looked to figure out):

Install/Enable the XML RPC Plugin for trac
Give your authenticated group the XML_RPC permission
Install/Enable the HttpAuth Plugin
Add this line to your apache config for your site: WSGIPassAuthorization On

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Easily Creating Fixed Length Flat Files With Groovy

Tim — Wed, 21 Jan 2009 13:42:27 +0000

Here's an (I think elegant) way to create flat files with Groovy.

I want this script to be easy to read by future developers. So if someone wants to know what the format of the file is they can see it just by opening the script.

Classes We'll Use

Groovy:

SQL: We'll use this library to access the database, it has some nice closure methods like eachRow which make iterating over results easy.
String: Groovy includes a string class that has some nice methods like padRight and padLeft, handy for making fixed length files.

Java:

File Writer: The easiest way to create files in java.

The Plan

Define our file in a map at the top of the file, it will be SQL Alias Name : Length.

Execute our SQL, for each row iterate through our file definition map and pad each value by the appropriate length.

The Code

Pretty self explanatory -- a few neat groovy things we use in this script:

Triple quotes for a multiline string (our sql)
The format method to easily format a date (bye bye simple date format) for the file name
The elvis operator ?: makes the results null safe so we can call padRight.
The each method on Groovy's Map that accepts a closure, we use that to iterate through our file definition.

import groovy.sql.Sql

import java.io.File;
import java.io.FileWriter;

def fileName = "FLATFILE" + String.format('%tY%,new Date()) + ".txt"

def sql = Sql.newInstance("jdbc:oracle:thin:@localhost:1521:midb01",
"xxx","xxx", //user,pass
"oracle.jdbc.driver.OracleDriver") //jdbc driver

FileWriter writer = new FileWriter(fileName);

//this map defines the field length based on alias id from the SQL
def fileDef = [COLUMN1:14,
COLUMN2:9,
COLUMN3:5,
COLUMN4:16]

def qry = """SELECT column1,column2,
column3,column4 FROM OurTable"""

def test = sql.eachRow(qry){row ->
fileDef.each{ k,v-> writer.append ((row[k] ?: " ").padRight(v))}
writer.append "\n"
}
writer.close()

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Limiting log4j SMTPAppender

Tim — Fri, 15 Feb 2008 14:43:21 +0000

I wanted to set a maximum amount of e-mails that SMTPAppender would send after filling up a mailbox with 30,000 damn e-mails.

Turns out it was pretty damn easy, I set up my appender in a java class, and the SMTP appender has a method called setEvaluator that takes an instance of TriggeringEventEvaluator, so I just created a quick inner class like so.

class LimitingEvaluator implements TriggeringEventEvaluator
{
private int sentEvents = 0;
private int MAX_EVENTS = 20;
@Override
public boolean isTriggeringEvent(LoggingEvent arg0) {
sentEvents++;
if(sentEvents>= MAX_EVENTS)
return false;
return true;
}

}

and when i set up my appender I do this

appender.setEvaluator(new LimitingEvaluator());

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Killing a process by name in ubuntu

Tim — Mon, 17 Sep 2007 20:52:23 +0000

I have to kill mongrel alot because it's a flea-bitten mutt.

My usual method was to do a ps -aux | grep mongrel , find the pid and kill it!

Annoying and stupid!

Now I just use the nice pkill tool in ubuntu like so.

pkill mongrel

boom! All bad doggies killed! This probably works on other *nix flavors, but who knows if your stupid admin installed it.

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Capturing STDERR with ruby backticks

Tim — Fri, 14 Sep 2007 14:13:25 +0000

I was writing a ruby script today that ran a linux command for every line in a file. The problem was the backtick operator in ruby only captures stdout, here's a little trick to get stderr as well. (*nix only)

out = `ourlinuxcmd 2>&1`

the 2>&1 bit tells the shell to redirect stderr to stdout

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Running rails with mongrel for a specific sub directory

Tim — Mon, 10 Sep 2007 13:20:54 +0000

I've started using mongrel for running rails apps with apache2 and mod_proxy , it works like a charm and allows you to run multiple rails apps and mongrel instances on one server.

Your proxy setup looks like this in your httpd.conf or vhost.conf

80>
ServerName myapp.com
ServerAlias www.myapp.com

ProxyPass /myapp http://www.myapp.com:8000/
ProxyPassReverse /myapp http://www.myapp.com:8000
ProxyPreserveHost on

Then in your environment.rb add:

ActionController::AbstractRequest.relative_url_root = '/myapp'

This will make ActionController rewrite the proper URL for your rails application.

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♥ HTML Heart Code ♥

Tim — Sat, 01 Sep 2007 21:21:16 +0000

Here's how you make a heart in HTML,

♥

Now, stop coming here for that! I'm sick of seeing you in my referral logs!

*Edit - Now i'm #1 in google for this unwillingly! Oh, well go ahead and try it out in the comments you weirdos.

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