I’m trying to fix a performance issue and can’t seem to get anywhere. During our daily busy period, our CPU usage recently began to peg at 100%. We are using Ignite, and it identified one query as being responsible for most of the CPU used during that period. The query is executing the sp_columns system stored proc, which returns information about a table column, given the table and column name. This query only recently started causing issues and I can’t figure out why it suddenly cropped up. Here is what I know:
Ignite shows that:
• The number of executions has not significantly changed
• The number of reads (logical and physical) has not significantly changed
• The number of writes has changed (3x more), but 7500 writes wouldn’t seem to peg the CPU even if they all happened at once.
• The largest wait for this sproc is “CPU”, and the days when things are bad the total CPU waits are 4-5x what they are on a good day.
• The query with the next largest CPU wait values is 1/5 this one.
Last time this happened we had 1-2 really bad days, then it disappeared. This time we’ve tried updating stats (on the non-system tables) and dumping the proc cache, without any noticeable improvement.
What I can’t figure out is why a system stored proc returning table metadata would tank like this out of the blue. We haven’t made any dramatic schema changes that would mean it was spinning through more data and the number of reads confirms that. The execution duration changes (2x) and the CPU changes (1.5x), but everything else stays the same.
Any ideas why this might be? Anyone familiar with Ignite that might know something Ignite is not showing me?