The Explain Query tool

When there’s a topic which has been challenging forever in the AEM world, then it’s JCR queries and indexes. It can feel like an arcane science, where it’s quite easy to mess up and end up with a slow query. I learned it also the hard way, and a printout of the JCR query cheatsheet is always below my keyboard.

But there were some recent changes, which made the work with query performance easier. First, in AEM CS the Explain Query tool has been added, which is also available via the AEM Developer Console. It displays queries, slow queries, number of rows read, the used index, execution plan etc. But even with that tool alone it’s still hard to understand what makes a query performant or slow.

Last week there was a larger update to the AEM documentation (thanks a lot, Tom!), which added a detailed explanation of the Explain Query tool. Especially it drills down into the details of the query execution plan and how to interpret it.

With this information and the good examples given there you should be able to analyze the query plan of your queries and optimize the indexes and queries before you execute them the first time in production.