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Published by Baron Schwartz on Feb 5, 2019 11:29:13 AM

The Left-Prefix Index Rule

There's an important heuristic in database indexing that I call the left-prefix rule. It helps you understand whether the database will be able to make the best use of a multi-column index to speed up a query. It's one of a small handful of really important things to understand about indexes!


The left-prefix rule can be confusing, but once you grok it, it's simple and easy to use. It applies to MySQL, PostgreSQL, MongoDB, and many other databases. In this post I'll explain what the left-prefix rule means and how it works.

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Published by Baron Schwartz on Feb 1, 2019 11:04:00 AM

Covering Indexes in MySQL, PostgreSQL, and MongoDB

A covering index is a fantastic query performance optimization. An index covers a query when the index has all the data needed to execute the query, so the server can retrieve the query’s data without reading any rows or documents. Covered queries are usually SELECT queries, but in addition to reads, indexes can cover portions of what a write query needs to do its work.

In this article I’ll explain what a covering index is in a bit more detail; the technical implementation and caveats in MySQL, PostgreSQL, and MongoDB; and how to check that a query is using a covering index.

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Published by Baron Schwartz on Jan 28, 2019 2:36:00 PM

What is Concurrency in a Database?

Databases are confusing! Not only are they complicated bits of software, but database jargon is really complicated. Part of this comes from the number of words that have multiple meanings: depending on which community you spend time in, there are multiple meanings for words like schema, cluster, and even database.

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Published by Baron Schwartz on Jul 30, 2018 1:47:27 PM

What is Cardinality in Monitoring?

I wrote a couple of “definitions and nuances” posts about terminology in databases recently (cardinality, selectivity), and today I want to write one about cardinality in monitoring, as opposed to cardinality in databases. If you’ve seen discussions of “high-cardinality dimensions” or “observability requires support for high-cardinality fields” this is what we’re talking about today. So what does it mean?

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Published by Samantha Toet on Jul 10, 2018 12:43:04 PM

VividCortex Welcomes Amena Ali as CEO

Exciting news: today we announced the appointment of Amena Ali as Chief Executive Officer and member of the Board of Directors. Company founder Baron Schwartz will now assume the role of Chief Technology Officer. “I am proud of the product and culture we’ve built,” said Baron. “I’ve always believed that the keys to a rewarding career are being challenged, making a meaningful impact, and working with delightful people. Amena joins at the perfect time to scale the company and team, while I redouble my focus on our customers and the product vision for the next wave of monitoring needs.”

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