The problem One common pattern we see in some analytical workloads is the repeated use of the same, often times expensive expression. Look at the following query plan for example: The expression JSON_PARSE(features) is used 6 times, and casted to different ROW structures for further processing. Traditionally, Presto would just execute the expression 6 times,…
In the previous article we looked at the abstract problem statement and possibilities inherent in scanning tables. In this piece we look at the quantitative upside with Presto. We look at a number of queries and explain the findings. The initial impulse motivating this work is the observation that table scan is by far the…
Table scan, on the face of it, sounds trivial and boring. What’s there in just reading a long bunch of records from first to last? Aren’t indexing and other kinds of physical design more interesting? As data has gotten bigger, the columnar table scan has only gotten more prominent. The columnar scan is a fairly…