Conference Schedule - PGConf.EU 2019

The TopN extension: Maintaining top 10 lists at scale

Date: 2019-10-17
Time: 11:50 - 12:40
Room: Foscolo
Level: Intermediate

Whether it's the biggest, oldest, fastest, slowest one of everyone's favorite questions about data is: What is the top 10? SQL offers easy solutions like "SELECT item, count(*) FROM data GROUP BY item ORDER BY 2 DESC LIMIT 10", but if you have a lot of data and a dashboard that can generate many ever-changing top 10 lists, then such queries don't scale at all. What we need is to be able to incrementally update top N lists as new data comes in. PostgreSQL did not have an easy way to do that yet, so we added it via the postgresql-topn extension.

In this talk, I will focus on the PostgreSQL extension postgresql-topn (new as of March 2018). TopN can provide approximate answers to these kinds of aggregation queries within reasonable and configurable error bounds. TopN is not only fast and memory-efficient but also has very interesting properties which especially shine in a distributed environment. In this talk, I will talk about the internals of TopN and how it estimates top items. At the end of this session, you will have fallen in love with the capabilities of TopN and you will be adding it to your analytics tool belt.


Furkan Sahin