Database server coordinator failure

The consistency of data after a coordinator failure depends on the point in the heterogeneous commit process at which the coordinator fails. If the coordinator fails before sending the commit message to the gateway, the entire transaction is stopped upon recovery, as is the case with two-phase commit.

If the coordinator fails after it writes the commit log record, the entire transaction is committed successfully upon recovery, as is the case with two-phase commit.

If the coordinator fails after it sends the commit message to the gateway but before it writes the commit log record, the remote HCL Informix® database server sites in the transaction are stopped upon recovery. This can result in inconsistencies if the gateway received the commit message and committed the transaction.

The following table summarizes these scenarios.
Point of database server coordinator failure Expected result
After the coordinator writes the PREPARE log record and before the gateway commit phase Data consistency is maintained.
After the coordinator sends a commit message to the gateway but before it receives a reply Data is probably inconsistent. No indication of probable data inconsistency from the coordinator.
After gateway commit phase but before the coordinator writes a COMMIT record to the logical log Data consistency is lost. No indication of data inconsistency from the coordinator.

Copyright© 2019 HCL Technologies Limited