Question

A load that has been running in about 2 minutes suddenly turned into a 90 minute run before being manually cancelled.

It’s a simple shadow query:

select fields
into shadow_table
from table
where date = '8/23/2011'

date has a non-clustered index on it.

If I change the query to select

• top 300000 it completes in 2 seconds
• top 400000 it runs in 3 minutes
• top 500000 I got bored waiting and cancelled it

Our server team shows a lot of self blocking while it runs.

Can anyone suggest possible bottlenecks to look at?

Answer 1

Out of date stats.

Self-blocking only occurs with parallelism, and super long parallel runs (compared to norms) ordinarily means out-of-date stats. It could also be a change in cardinality in the data.

Step 1 should be running an UPDATE STATISTICS WITH FULLSCAN on your source table.