Introduction In this article, we are going to see how Index Selectivity works in relational database systems and why the database Optimizer might choose to avoid using an index if the number of matching records is large. Index selectivity is inversely proportional to the number of index entries matched by a given value. So, a unique index has the highest…
#index
6 posts
22 Nov 2023
28 Feb 2018
In the previous post, we talked about one of the talks I gave at the Index Developer Conference last week. In this post, we share the materials from the other one, titled How we built a global search engine for genetic data. The session was scheduled in the Real-life production deployments track. Unlike the talks I usually...
27 Feb 2018
Index Developer Conference is a new conference organized by IBM to promote software development as a craft. The event took place at the Moscone Center, San Francisco, a popular software conference venue, on February 20-22, 2018. This was my first conference of the year and I was very excited about being invited to give 2 talks in 2...
18 Jan 2017
A very interesting feature of the SQL Server and PostgreSQL databases (and some others, including SQLite) is the partial index (sometimes also called “filtered index”). That’s an index that contains only “parts” of the table data. For instance, we can write the following index in SQL Server and PostgreSQL: Let’s imagine you have a house … Continue reading How to…
28 Apr 2015
I keep encountering situations where RDBMS users think that one second for query execution is anything near fast. Most recently, in this Stack Overflow question: Hibernate SQL In clause making CPU usage to 100% The poster’s original question was why a similar query executes in one second when executed in SQL Server Management Studio whereas … Continue reading Do Not…
12 May 2014
Recently, at the office: Bob: I’ve looked into that slow query you’ve told me about yesterday, Alice. I’ve added the indexes you wanted. Everything should be fine now Alice: Thanks Bob. I’ll quickly check … Nope Bob, still slow, it didn’t seem to work Bob: You’re right Alice! It looks like Oracle isn’t picking up … Continue reading The Index…