Fix Stale Reads on MySQL in Event Notifications DAO

[ThiwankaChanditha]

Problem

In MySQL InnoDB (default REPEATABLE READ isolation level), read queries executed with autoCommit = false establish an MVCC transaction snapshot. Because read operations in event.notifications.dao did not call commitTransaction before returning connections to the Tomcat JDBC pool, connections remained active with uncommitted, frozen snapshots. When requests reused those connections after writes, newly committed records were invisible, causing {"items":[],"total":0} list responses and EN-4040: No subscription exists errors. Reference #107

Scope of Changes

Per ownership boundaries, changes are strictly isolated to org.wso2.dpdp.accelerator.event.notifications.dao:

1. SubscriptionDAOImpl.java:

   • Added explicit DatabaseUtils.commitTransaction(conn) on success and DatabaseUtils.rollbackTransaction(conn) on catch across:
     • getSubscriptionById(String, String)
     • listSubscriptions(...)
     • getPurposesBySubscriptionId(String, String)
     • countActiveSubscriptionsForTopic(String, String)
     • getPurposesBySubscriptionIds(List<String>)
     • hasPendingOrInFlightDeliveries(String, String)
     • getPendingSubscriptionsForRecovery(Timestamp, int)
   • Inner overloads accepting Connection conn remain untouched.

2. TopicDAOImpl.java:

   • Added commitTransaction(conn) on success and rollbackTransaction(conn) on catch across:
     • getTopicById(String, String)
     • getTopicByOrgAndName(String, String)
     • listTopics(...)

3. EventDAOImpl.java:

   • Added commitTransaction(conn) on success and rollbackTransaction(conn) on catch across:
     • getEventById(String, String)
     • getEventPurposes(String)
     • hasActiveEventsForTopic(String)
     • searchEvents(...)

4. DeliveryDAOImpl.java:

   • Added commitTransaction(conn) on success and rollbackTransaction(conn) on catch across:
     • getWebhookDeliveryById(String, String)
     • loadDispatchContexts(String, int)
     • loadDispatchContextsWithCutoff(String, int, Timestamp)
     • getWebhookDeliveryAudits(String, String)
     • getPollDeliveryById(String, String)
     • getPendingPollDeliveries(...)
     • listSubscriptionDeliveries(...)
     • getSubscriptionDeliveryById(...)
     • listOrgDeliveries(...)
     • getOrgDeliveryById(...)
     • listEventDeliveries(...)

5. DeliveryAckDAOImpl.java:

   • Added commitTransaction(conn) on success and rollbackTransaction(conn) on catch in getDeliveryAckByDeliveryId(String).

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Verification & Testing

1. Automated Unit Tests

• Command:

  mvn test -pl dpdp-accelerator/components/org.wso2.dpdp.accelerator.event.notifications.dao

• Results:
  • Tests run: 62, Failures: 0, Errors: 0, Skipped: 2
  • Status: BUILD SUCCESS

2. Manual Testing & Verification

Manual end-to-end tests were performed against a live WSO2 IS instance with MySQL Community Server 8.0:

1. Pre-fix Reproduction Test:

   • Pre-warmed multiple connection pool leases by issuing 6 parallel GET /subscriptions requests.
   • Inserted a new subscription via POST /subscriptions (15cb9fa6-8a98-4960-89b3-9d0e1bab554a).
   • Immediately issued 8 concurrent GET /subscriptions requests.
   • Observed Bug Behavior: 6 out of 8 requests returned stale count (total: 10) while only 2 returned the fresh count (total: 11), confirming that uncommitted pooled connections were serving frozen snapshots and omitting newly created records. Direct fetch on stale connections yielded EN-4040: No subscription exists with the specified ID for this organization. (404 Not Found).

2. Post-fix Verification Test:

   • Re-executed the same parallel workflow with the updated DAO bundle deployed.
   • Observed Fixed Behavior: All concurrent GET requests consistently returned the updated total count with 100% consistency, and individual GET /subscriptions/{id} calls consistently returned 200 OK with the active subscription details.
   • Verified that no stale connections or frozen snapshots remain in the Tomcat JDBC connection pool after read requests.

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