When you push too much paper into your shredder, it jams; when you pour too much coffee into your cup, it overflows; when you eat too much food, you…well, you know. Everything’s got limits.

One thing that grabbed my attention when I first joined Teradata back in '88, and that I still find striking today, is how the database manages the level of work that enters the system. Managing the flow of work inside Teradata is decentralized, low-effort, and scalable, exhibiting control at the lowest possible level—at the AMP.

I was asked the other day about the request cache, speficially, how to keep plans in the cache so the query does not have to undergo repetitive parsing and optimizing.  A request cache exists on each parsing engine (PE) and will hold generic plans that have been identified as potentially re-usable. For very short queries, request cache hits can reduce your elapsed time and provide more consistent response time. So the longer those re-usable plans stay in the cache, the better.

Michael McIntire’s recent posting on NoPI tables (read it now!) got me thinking more and more about mini-batch, and how it’s growing in popularity. Mini-batch is a technique that lets you update database tables in small batches several, many times a day using batch approaches. This could be a little batch job every hour, or it could be every 5 minutes, whatever frequency you choose.

The question of what Estimated Processing Time actually is comes up a lot. For example, the DBQLogTbl table carries an “EstProcTime” Value. If you are EXPLAIN-savy, then you’ve bumped up against “Estimated Time” numbers in almost every step of every query plan you’ve ever looked at. You TASM users frequently rely on “Estimated Processing Time” as a classification criteria to manage the priority that a query will enjoy. Some think Estimated Processing Time is an estimate of clock seconds, and others believe it represents CPU seconds.

Should you drop all Multicolumn statistics that are over 16 bytes?  No. There’s no need to go to that extreme. But let’s take a moment to consider the pros and cons of doing so, and how the 16-byte limit actually impacts you, or not.