Improving speed using clustered tables
In this section, you’ll learn about the power of correlation and clustered tables. What’s this about? Imagine that you want to read a whole area of data. This might be a certain time range, a block, some IDs, and so on.
The runtime of these queries will vary depending on the amount of data and the physical arrangement of data on the disk, so even if you’re running queries that return the same number of rows, two systems might not provide the answer within the same period as the physical disk layout might make a difference.
Here’s an example:
test=# EXPLAIN (analyze true, buffers true, timing true) SELECT * FROM t_test WHERE id < 10000; QUERY PLAN ---------------------------------------------------------- Index Scan using t_test_id_idx on t_test...