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Deep Tech Reference

This section dives into the low-level mechanics of QuickFIX/J. It is meant for core contributors, infrastructure engineers, or developers pushing the engine to its limits in high-frequency or complex environments.

Custom DataDictionaries​

Exchanges rarely follow the vanilla FIX specification perfectly. They frequently add custom tags, require tags that are officially marked as optional, or define entirely proprietary message types.

To handle this, you must modify the XML DataDictionary. The dictionary defines the grammar of the protocol.

Modifying the XML Dictionary​

Locate the FIX44.xml (or relevant version) file in the QuickFIX/J jar, copy it to your local filesystem, and point your configuration DataDictionary=my_custom_FIX44.xml to it.

<!-- Example: Adding a custom tag to NewOrderSingle -->
<message name="NewOrderSingle" msgtype="D" msgcat="app">
    <field name="ClOrdID" required="Y"/>
    <field name="Account" required="N"/>
    
    <!-- Custom exchange tag 9001 -->
    <field name="ExchangeSpecificData" required="Y"/> 
</message>

<!-- You must also define the tag in the fields section -->
<fields>
    <field number="9001" name="ExchangeSpecificData" type="STRING"/>
</fields>

When you define UseDataDictionary=Y, QuickFIX/J validates incoming bytes against these rules. If a required tag (like ExchangeSpecificData) is missing, QuickFIX/J will automatically generate a Reject (MsgType 3) and prevent the malformed message from reaching your Application's fromApp method.

Message Store Internals & Performance​

QuickFIX/J uses the MessageStore to guarantee delivery. When an application calls Session.sendToTarget(), the message is appended to the store before being flushed to the socket.

MemoryStore vs. FileStore​

  • MemoryStore: Yields zero disk I/O overhead. Because state is lost on JVM restart, sequence numbers will revert to 1. This is best for internal testing, market data feeds, or connections that do not strictly enforce intraday sequencing.
  • FileStore: Provides standard durability. To optimize for low-latency trading:
    • Ensure the storage directory is mounted on a high-speed NVMe SSD or a RAM disk (tmpfs).
    • If absolute durability is not critical on every tick, rely on the OS filesystem cache (as QuickFIX/J FileStore relies on standard RandomAccessFile appending).

Threading Details (Apache MINA)​

QuickFIX/J utilizes Apache MINA IoAcceptor and IoConnector for network transport. By default, SocketInitiator and SocketAcceptor create a pool of NIO threads.

Tuning Options:

  • SocketThreadPriority: Modifies the JVM thread priority of socket reading threads.
  • SocketUseOio: Reverts from non-blocking NIO to Old I/O (blocking sockets) if set to Y. Generally not recommended unless diagnosing specific network card offloading or kernel-level buffering issues.
  • SocketSendBufferSize / SocketReceiveBufferSize: Tunes the underlying TCP socket buffer sizes.

JMX Integration​

QuickFIX/J provides a comprehensive MBean hierarchy allowing you to inspect session state, reset sequence numbers, and trigger manual logons/logouts without restarting the JVM.

Registering the JMX Exporter​

import org.quickfixj.jmx.JmxExporter;

// After creating your Acceptor or Initiator
Initiator initiator = new SocketInitiator(...);
initiator.start();

JmxExporter exporter = new JmxExporter();
exporter.register(initiator);

Once registered, you can connect to your application via JConsole, VisualVM, or Datadog/Prometheus JMX agents to explore the org.quickfixj domain. You can monitor attributes like IncomingSequenceNumber and OutgoingSequenceNumber in real time.

Dynamic Sessions​

For gateway architectures where a server accepts connections from an unknown or dynamic list of clients, pre-configuring every session in the [SESSION] block is unfeasible.

QuickFIX/J provides DynamicAcceptorSessionProvider. When a new connection arrives and a Logon (35=A) is received, the Acceptor consults the provider. If the provider approves the SenderCompID and TargetCompID, QuickFIX/J dynamically instantiates a new Session in memory and fires onCreate in your Application.