If you work with I/O benchmarking of Oracle databases, you are almost certainly familiar with SLOB. SLOB is more than just an I/O benchmark — it’s become a de-facto industry standard. It’s simple, powerful and efficient, and it captures a plethora of metrics, both from the OS (output of iostat, mpstat etc.) and the database itself (in the form of an AWR report).
One thing that is missing though is visualization. It’s fairly easy to fix using an external plotting tool (like gnuplot or R), but what data would you plot? AWR only gives you average event times and histograms with ridiculously poor resolution. And if you want to see a high-resolution picture of your I/O (and you do — I’ll discuss the importance of that later on), it’s not enough.
Continue reading “Plotting SLOB results in high resolution”
In this article, I’ll summarize my observations regarding nested loop join mechanisms as well as previously known facts, so that everything would be in one place.
Continue reading “Nested loop internals — summary”
In the previous parts (here and here) of the series we looked at some aspects of nested loop I/O optimizations, but we have left out the most important question (from the practical point of view): how these methods are doing time-wise? Which one(s) is(are) faster, and how much savings are they offering compared to the non-optimized plan? We will turn to these questions now.
Continue reading “Nested loop internals. Part 3: comparative efficiency”
In the previous part of this mini-series we looked at differences in multiblock read behavior for different nested loop optimization mechanisms depending on degree of ordering of the data. In this post I’ll continue to explore the subject, but this time we’ll focus on decision-making process: what factors (other than the obvious ones — like optimizer hints and/or parameters) affect the specific choice of a mechanism?
Continue reading “Nested loop internals. Part 2: decision making”