eXist

Chapter 4. Architecture

In this chapter we look in detail at how eXist is constructed and how it processes your XML documents and executes your XQueries. This information should be considered advanced, so if you are a beginner you may want to skip to another chapter. However, for those wishing to master eXist, this information can be invaluable in helping you understand how to use it efficiently.

eXist is a large software project that has evolved over the last 13 years, and is written predominantly in the Java programming language. Although extensions and add-ons to eXist are often written in pure XQuery and/or XSLT, the main body of eXist is written in Java.

Regardless of how you decide to deploy and use eXist, its architecture (see Figure 4-1) predominately remains the same, with various optional components depending on your use.

Figure 4-1. Complete high-level diagram of eXist’s architecture

Each connection from an API to eXist is a single thread that interacts with the broker pool, which is configured with a number of brokers (20 by default). Each broker is a thread that interacts with the database, and represents a database request; this might be a database update operation (add/delete/store/update) or a query operation (XPath, XQuery, or XSLT). Should you connect to eXist and all the brokers are busy, your request will pause until a broker becomes available to service your request. ...