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MOSS 2007 list performance drop

Observation : MOSS 2007 list performance drop

Recently, we discovered that the performance of the MOSS 2007 implemenation of our client dropped significantly for a specific list. The list contains some 1200 records. Most of them contain attachments. The loadtime for the default view would extend to over 20 seconds. Switching views made things even worse!

Analysis

First, the server performance was consulted while loading the list. No special or irregular behaviour of the processor or memory. Services were checked to find out if a service like for example the search was performing a heavy index. No special observations. Then we placed indexes on the key columns. This made no visible difference in performance.

How is it possible that only that list is slow in loading, while other list and doclibs in that same site have a normal loadtime? It had to be something list-specific. And what is specific to a list?  It's views...

Interpretation : Optimizing the GROUP BY

After scrutinizing the views of that list, we discovered that the there were massive groups in certain views. The "group by" statement resulted in records being categorized in over 100 groups. Setting a limit to the number of groups improved performance drastically!
When showing 100 groups on a page, the loadtime took 15-20 or even more seconds. When tuning down the number of groups to 50, the page loaded under 10 seconds.

We tested further and discovered that the number of items under a group hardly alter the page loading time when the groups are collapsed on start. A page with 1 group and 500 items under it will load many times faster than a page with 500 groups and just 1 item under each of those groups.
The key is be wise with GROUP BY statements.

Conclusion : Relation between GROUP BY statement and load time

  1. Group your items in less then 50 categories for optimal performance
  2. Show as few groups as possible on a page (max 50 groups/page)
  3. Place column indexes on the columns you group by 

Applying these principles solved our issue on the spot...

We hope this information will help you further optimizing your WSS/MOSS 2007 environment.