I'm involved in an implementation of doing trigger-based counting as a substitute for count( * ) in real time in an application. My trigger-based counts seem to be working fine and dramatically improve the performance of the display of the counts in the application layer.

The problem comes in importing new data into the tables for which the counts are maintained. The current import process does some preprocessing and then does a COPY from the filesystem to one of the tables on which counts are maintained. This means that for each row being inserted by COPY, a trigger is fired. This didn't seem like a big deal to me until testing began on realistic data sets.

For a 5,000-record import, preprocessing plus the COPY took about 5 minutes. Once the triggers used for maintaining the counts were added, this grew to 25 minutes. While I knew there would be a slowdown per row affected, I expected something closer to 2x than to 5x.

It's not unrealistic for this system to require data imports on the order of 100,000 records. Whereas this would've taken at most an hour and a half before (preprocessing takes a couple of minutes, so the actual original COPY takes closer to 2-3 minutes, or just over 1500 rows per minute), the new version is likely to take more than 7 hours, which seems unreasonable to me. Additionally, the process is fairly CPU intensive.

I've examined the plans, and, as far as I can tell, the trigger functions are being prepared and using the indexes on the involved tables, which are hundreds of thousands of rows in the worst cases. The basic structure of the functions is a status lookup SELECT (to determine whether a count needs to be updated and which one) and one or two UPDATE statements (depending on whether both an increment and a decrement need to be performed). As I said, it looks like this basic format is using indexes appropriately.

Is there anything I could be overlooking that would tweak some more performance out of this scenario?

Would it be absurd to drop the triggers during import and recreate them afterward and update the counts in a summary update based on information from the import process?


Thomas F. O'Connell
Co-Founder, Information Architect
Sitening, LLC
110 30th Avenue North, Suite 6
Nashville, TN 37203-6320

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