Boost Tomcat Performance: Master BIO, NIO, and APR Modes with JVM Tuning

Tomcat has three operating modes

BIO : the default mode, very low performance and not optimized.

NIO : uses Java's asynchronous (non‑blocking) I/O. To enable, edit the <Connector> node in server.xml and set protocol="org.apache.coyote.http11.Http11NioProtocol".

<Connector port="80"
           protocol="org.apache.coyote.http11.Http11NioProtocol"
           connectionTimeout="20000"
           URIEncoding="UTF-8"
           useBodyEncodingForURI="true"
           enableLookups="false"
           redirectPort="8443">

APR : solves asynchronous I/O at the OS level, greatly increasing performance. It requires installing APR and the Tomcat native library, then switching the protocol to org.apache.coyote.http11.Http11AprProtocol.

Install APR

yum -y install apr apr-devel

Install native library

cd /usr/local/tomcat/bin/
 tar xzfv tomcat-native.tar.gz
 cd tomcat-native-1.1.20-src/jni/native/
 ./configure --with-apr=/usr/bin/apr-1-config
 make
 make install

After installation you will see:

Libraries have been installed in:
   /usr/local/apr/lib

Add the library path to Tomcat: CATALINA_OPTS="-Djava.library.path=/usr/local/apr/lib" Change the connector protocol in conf/server.xml: protocol="org.apache.coyote.http11.Http11AprProtocol" When Tomcat starts, the log will contain:

INFO: APR capabilities: IPv6 [true], sendfile [true], accept filters [false], random [true].

Concurrency Optimizations

1. JVM tuning : add the following to catalina.sh (adjust values as needed):

JAVA_OPTS="-Xms1024m -Xmx1024m -Xss1024K -XX:PermSize=64m -XX:MaxPermSize=128m"

Parameter meanings:

-Xms: initial heap size

-Xmx: maximum heap size

-Xss: thread stack size

-XX:PermSize / -XX:MaxPermSize: non‑heap memory for class metadata

Recommendations: set -Xms and -Xmx to the same value (60‑80% of physical RAM); thread stack size around 256K; adjust non‑heap size based on application.

Example for a 32 GB machine:

JAVA_OPTS="-Xms20480m -Xmx20480m -Xss1024K -XX:PermSize=512m -XX:MaxPermSize=2048m"

2. Disable DNS reverse lookup : add enableLookups="false" to the <Connector> element.

3. Optimize Tomcat connector parameters (using APR) :

<Connector port="8080"
           protocol="org.apache.coyote.http11.Http11AprProtocol"
           connectionTimeout="20000"
           redirectPort="8443"
           maxThreads="500"
           minSpareThreads="20"
           acceptCount="1000"
           enableLookups="false"
           URIEncoding="UTF-8" />