Question

The project is a web app in ASP/VB.net. The issue is that some pages are mind-boggingly slow. After trying to track down the bottleneck, it was discovered to be the load method when filling a datatable with query results.

We are using an Oracle database and queries are executed in stored procedures. As an example, we have a relatively simple select statement within a procedure which returns 2 columns with 6 rows which was determined to take about 0.015 seconds to execute. However it takes on average 7 seconds to load the OracleDataReader into a datatable – a ridiculous amount of time for such a small record set. After messing around with the query, I found that a simple decode statement appeared to be causing the issue. The decode statement is used similar to as follows:

WHERE
DECODE(iBln, 1, column1, column2) BETWEEN iDate1 and iDate2

The iBln variable is simply a number being passed in to act as a boolean variable for determining which column should be between two dates. If I comment this decode statement out and make it simply “column1 BETWEEN iDate1 and iDate2” then the load method takes no time at all as it should, signifying that it is indeed the decode statement causing issues.

So I’m just hoping to hear from anyone that could have an idea as to what’s causing this or how to fix it. It’s a simple decode, how does it even affect the load method anyway?

Answer 1

I would verify that indexes exist for column1 and column2. If so, the likely problem is that the DECODE is preventing the use of the indexes. Try rewriting as:

WHERE ( ( iBin = 1 AND column1 BETWEEN iDate1 AND iDate2)
        OR
        ( (iBin IS NULL OR iBin <> 1) AND column2 BETWEEN iDate1 AND iDate2)
      )