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HeliosDB HeliosProxy

Example — failover-demo

Example — failover-demo

Manual primary-failover demo with Transaction Write Replay (TWR) on the proxy side.

Source on GitHub: HeliosDB-Proxy/examples/failover-demo

Demonstrates

  • Application connects to the proxy on :5432 and starts a long-running transaction
  • Operator triggers pg_promote on the standby; primary goes down mid-transaction
  • HeliosProxy detects the failover and, with tr_mode = "transaction", replays the uncommitted transaction against the new primary — verifying each replayed response against the digest of what the client already saw, and rolling back with SQLSTATE 40001 on any divergence
  • The application keeps its connection and the transaction commits on the new primary; had the COMMIT itself been in flight, the client would get SQLSTATE 08007 and the COMMIT would not be retried
  • Had the transaction been opened at SERIALIZABLE or REPEATABLE READ, it would not have been replayed at all — no replacement backend can reproduce that snapshot
  • This needs no cargo feature: in-session replay is core. ha-tr is what adds the separate write journal and the /api/replay endpoint below

Run

Terminal window
cd HDB-HeliosDB-Proxy/examples/failover-demo
./run-demo.sh

The driver script narrates each step. Watch the proxy admin UI’s Topology panel to see the failover in real time. The Time-Travel Replay panel reads the separate ha-tr write journal, which is populated by the write path rather than by the session recovery — it is a different view, not a trace of the replay you just watched.

Why it matters

This is the demo that maps directly to Innovation #6 (Transaction Write Replay) in the HeliosProxy IP portfolio — Oracle TAF/TAC-equivalent failover transparency without per-application code changes.