Unix Math Calculations

I just ran across http://x-bc.sourceforge.net/index.html. If you've ever used the Unix bc calculator utility, this project provides two excellent extensions to the built in capabilities of the calculator. In particular:

http://x-bc.sourceforge.net/extensions_bc.html

http://x-bc.sourceforge.net/scientific_constants_bc.html

You'll get a wealth of math functions available to you by simply including the extension files avaiable at those URLs.

In order to have these extensions always loaded as well turn on the built in math extensions, you can alias your bc command as follows:

alias bc="bc -l ~/bin/*.bc"

Apache Tomcat DBCP Connection Pooling

I've been looking at some performance issues with our Tomcat servers (we have many) and have seen some real inconsistency in the DBCP options that are specified. In general the basic ones you'd expect to see are there: a validation query, minIdle, maxActive. However, other ones are missing. This page http://commons.apache.org/dbcp/configuration.html lists the options and gives a good explanation of each. Everyone using Tomcat and DBCP should review this list and understand them.

A couple of interesting options to point out are those dealing with the validity of idle connections in the pool:

testWhileIdle (default false)

The indication of whether objects will be validated by
the idle object evictor (if any). If an object fails to
validate, it will be dropped from the pool. NOTE - for
a true value to have any effect, the validationQuery
parameter must be set to a non-null string.

timeBetweenEvictionRunsMillis (default -1)

The number of milliseconds to sleep between runs of the
idle object evictor thread. When non-positive, no idle
object evictor thread will be run.

numTestsPerEvictionRun (default 3)

The number of objects to examine during each run of the
idle object evictor thread (if any).

minEvictableIdleTimeMillis (default 1000 * 60 * 30)

The minimum amount of time an object may sit idle in
the pool before it is eliga

A good blog post on Apache DBCP can be found on Roy's Musings under Gotchas with DBCP.

For a comparison of Apache DBCP with another connection pool see Vigil Bose's Blog.

Also check out BoneCP for a connection pool specifically written to be fast.

Change a text cell into a Hyperlink in Excel

I recently imported a CSV file I was given into Excel. The file had two columns (with many rows of data) that contained URLs in the format http://foo.com/bar?phuid=1023, etc. I wanted to make these links clickable. Excel provides a straight forward, but manual way to do this. I asked around for an automated way to do this and was quickly given this macro:

Sub URL_List()
   For Each cell In Selection
       If cell.Value <> "" Then
           If Left(cell.Value, 7) = "http://" Then
               URL = cell.Value
           Else
               URL = "http://" + cell.Value
           End If
           ActiveSheet.Hyperlinks.Add Anchor:=cell, _
             Address:=URL, TextToDisplay:=cell.Value
       End If
   Next cell
End Sub

I don't know the source of this macro it proved useful today. I hope you can make some use of it.

The directions on creating a macro in Excel can be found in Excel's help which I'll repeat here:

Create a macro using Microsoft Visual Basic

1. On the Tools menu in Microsoft Excel, point to Macro, and then click Visual Basic Editor.


2. On the Insert menu, click Module.


3. Type or copy your code into the code window of the module.


4. If you want to run the macro (macro: An action or a set of actions that you can use to automate tasks. Macros are recorded in the Visual Basic for Applications programming language.) from the module window, press F5.


5. When you're finished writing your macro, click Close and Return to Microsoft Excel on the File menu.