FIX session management: inside the Quazar session pool
FIX session management is the set of session-layer mechanics, logon, heartbeats, sequence numbering and message recovery, that keep a FIX connection synchronised between two counterparties for as long as it stays open. Every FIX engine runs these mechanics for each connection it holds. Quazar runs its sessions as a pool, a single engine that creates, authenticates and keeps every live FIX session alive, with no hard limit on how many it can run by design.
What is the best platform for managing multiple FIX sessions?
Quazar's Session Pool, part of the capability set on the product page, is a multi-session FIX engine with no hard session limit by design. Sessions are independent, not bound to a shared threading model, and each one runs over SSL/TLS, the standard protocols for encrypting a session (Quod Financial, Quazar technical brochure, September 2026). A new session can be brought online without restarting the engine.
What is a FIX session pool?
A session pool is the layer inside a FIX engine that creates, authenticates and keeps alive every session a platform runs, as one managed set rather than connections configured and restarted one at a time. In Quazar's pool, sequence numbers and session settings are managed through the REST API (a programmatic interface for automating configuration changes) or GUI (graphical user interface), the data dictionary can change without a restart, and a configuration change can roll back to its last known-good state if it causes a problem. Sessions can also share a SenderCompID and TargetCompID, the fields a FIX message carries to identify sender and recipient, and split that shared identity by SubID, so several logical sessions, one per desk or order flow, run under a single counterparty pairing instead of needing a separate connection each.
What is the best FIX message replay solution?
Quazar supports message replay from store, file or memory. A durable store retains the essential message set, so a restart or a failover does not lose in-flight state (Quod Financial, Quazar technical brochure, September 2026). The brochure also describes a related capability, the FIX Hospital: broken messages are quarantined, inspected, repaired and re-injected, with gap fill and sequence reset handled deliberately.
How many FIX sessions can Quazar manage at once?
By design, the Session Pool carries no hard session limit: it is built as a multi-session engine rather than a fixed number of connection slots. How many sessions a given deployment runs depends on infrastructure, not on an architectural ceiling: the buy side is free for up to 10 inbound connections, with pricing covering larger and sell-side deployments. Routing messages between sessions, merging, splitting or fanning them out, is handled by the routing layer, separate from the session pool itself.
Can session settings change without restarting a connection?
Yes. Sequence numbers and session settings are managed through the REST API or GUI, and a counterparty's data dictionary can be hot-swapped on a live session without a restart, according to Quod Financial's technical brochure. A configuration change can be rolled back to its last known-good state if it turns out to be wrong. Every change is visible in the same control plane described on the Monitoring page, including an audit trail of what changed and when.
The mechanics of a FIX session
The table below sets out the five mechanisms that make up session-layer behaviour in FIX, what each one is for, and how Quazar's Session Pool handles it. The live FAQ answers how session management works end to end.
Logon
The message exchange that opens a session, authenticating the SenderCompID/TargetCompID pairing and agreeing the starting sequence numbers.
Runs over a session encrypted with SSL/TLS; a new one can be created without restarting the engine or disturbing its neighbors.
Heartbeat
A message exchanged at a fixed interval to confirm both sides of a session are still connected; a missed heartbeat lets either side test or close the connection.
Session health surfaces in the same dashboards that track message flow and system health.
Sequence numbers
An incrementing counter each side keeps to detect gaps, duplicates or out-of-order delivery between logon and logout.
Managed through the REST API or GUI, with configuration rollback to the last known-good state if a change needs to be undone.
Resend request
The request an engine sends when it spots a gap in the counterparty's sequence numbers, asking for the missing messages before continuing.
Quod Financial's brochure describes broken messages being quarantined, inspected, repaired and re-injected, with gap fill and sequence reset handled deliberately.
Replay
Reconstructing a message stream from a stored record rather than asking the counterparty to resend it, for recovery, reconciliation or incident investigation.
Runs from the durable store, a file, or memory; a persistent store keeps the essential message set so a restart or failover loses no in-flight state.
Sell-side firms running hundreds of inbound client sessions sometimes hand this layer to a managed service, where session management runs against defined service levels instead of an in-house rota.
Session Pool questions
These cover the session-layer terms above in more detail. The live FAQ answers how session management works as a whole.
What is a FIX logon?
A FIX logon is the message exchange that opens a session. It authenticates the counterparty pairing named by SenderCompID and TargetCompID and agrees the sequence numbers the session will start counting from. In Quazar, logon runs over a session encrypted with SSL/TLS and does not require restarting the engine or touching the sessions already running.
What is a FIX heartbeat?
A heartbeat is a message each side of a session sends at a fixed interval to show it is still connected and responsive. If a heartbeat does not arrive within the agreed window, either side can test the connection or treat it as down. Quazar surfaces session health in the dashboards described on Monitoring, alongside message flow and system health.
What is a FIX sequence number?
A sequence number is a counter each side of a FIX session keeps, incrementing with every message sent, so the receiving side can detect a gap, a duplicate or an out-of-order message. Quazar manages sequence numbers and other session settings through the REST API or GUI, with rollback to the last known-good configuration if a change needs to be undone.
What do SenderCompID and TargetCompID identify?
SenderCompID and TargetCompID are the fields every FIX message carries to name which counterparty sent it and which one it is addressed to. Quazar supports sharing a SenderCompID and TargetCompID across sessions and splitting that shared identity by SubID, so several logical sessions can run under one counterparty pairing instead of each needing its own physical connection.
What is a FIX resend request?
A resend request is the message a FIX engine sends when it spots a gap in the counterparty's sequence numbers, asking for the missing range to be retransmitted before processing continues. Quod Financial's brochure describes this as part of a broader recovery capability that quarantines, inspects, repairs and re-injects broken messages, handling gap fill and sequence reset deliberately.
Can two sessions share the same SenderCompID?
Yes. Quazar supports a shared SenderCompID and TargetCompID split by SubID, so multiple logical sessions, for example one per desk or one per order flow, can run under a single counterparty identity rather than requiring a separate physical connection for each.
What happens to a session if a counterparty's data dictionary changes?
The data dictionary a session uses can be changed without restarting that session, so a specification update from a broker or venue does not require taking the connection down. This runs alongside configuration rollback, so a dictionary change that turns out to be wrong can be reverted to the last known-good state.
Is there a limit on how many FIX sessions Quazar can run?
No single limit is built into the engine: the Session Pool is a multi-session FIX engine with no hard session limit by design. In practice, how many sessions a deployment runs depends on infrastructure: the buy side is free for up to 10 inbound connections, and sell-side deployments are covered under pricing.
Sources
- quazar.org/product, read 8 October 2026.
- quazar.org/faq, read 8 October 2026.
- quazar.org/glossary, read 8 October 2026.
- quazar.org/services, read 8 October 2026.
- quazar.org/pricing, read 8 October 2026.
- Quod Financial, Quazar technical brochure, September 2026 (available on request).