(This applies to Java and C, but the code is given in Python for readability.)

Is it faster to iterate over multiple separate arrays (tuples) of simple variables?

for i in range(0, n):
	phone = phones[i];
	# ...
	email = emails[i];

Or over a single array of complex variables?

for i in range(0, n):
	phone = people[i].phone;
	# ...
	email = people[i].email;

One array is faster than multiple arrays. This is because an array is stored in a contiguous block of memory. Accessing data in different arrays at the same time can require several different pages to be loaded from virtual memory. Memory access, especially hard drive access, is slow. As your application and data set grows, a significant performance difference may manifest itself.

Arrays from the Second Dimension

When iterating over a multidimensional array with indexes i and j, is it faster to iterate over j inside i?

for i in range(0, n):
	for j in range(0, m):
		cell = cells[i][j];

Or over i inside j?

for j in range(0, m):
	for i in range(0, n):
		cell = cells[i][j];

In Java and C, a multidimensional array[n][m] is stored as contiguous m-block of contiguous n-blocks. Let i be in n and j be in m. For a given i-cell, j-cells will be far apart. For a given j-cell, i-cells will be adjacent. Accessing adjacent values in memory is always faster.

For an array[i][j], putting j in the outer loop and i in the inner loop will significantly reduce potential virtual memory slowdowns.

This is the right way:

for j in range(0, m):
	for i in range(0, n):
		cell = cells[i][j];

The above only makes a difference with large data sets, but I like to cultivate good habits.

While writing a DB2 stored procedure that invoked a SOAP/WSDL web service using Apache Axis as part of WSIF, I ran into this doozie:

Ultimately, it’s caused by a too restrictive lib/security/java.policy file that ships with DB2.

Wrong Solution

The standard way to define an implementation is to create the following commons-logging.properties file and place it anywhere in your CLASSPATH (such as the root of a JAR file):

Alternatively, you can set the org.apache.commons.logging.Log configuration attribute for LogFactory programmatically.

Right Solution

Solution: Running an Axis SOAP client in Domino [or DB2]

My DB2 is installed into C:\Program Files\IBM\SQLLIB

1. Copy all your JARs to C:\Program Files\IBM\SQLLIB\java\jdk\jre\lib\ext
2. Open C:\Program Files\IBM\SQLLIB\java\jdk\jre\lib\security\
3. Open java.policy
4. Add:

5. Restart DB2