Tuesday, May 3, 2011

Splitting Queries...

I ran into a issue with a query which was running very slow. The query was returning only two columns but there was join between six to seven tables. When we had to move to a different server for development, the performance of the query went down even further. On examining the query, i found certain conditions in the where clause which were being repeated, also there were two conditions as part of the where clause which were linked by a OR condition like . One of the approaches i took was that I took the query with the seven table join and split it into two queries. I re-ran the query after the split and the performance greatly improved, it was taking 30 mins to execute when it was one big query. After the split i got the same results and execution time was 3 minutes. In a nutshell where there are lot of tables say more than 4 being joined, one needs to analyze the query and see if the results can be achieved in a faster manner in case the performance is bad.

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