Condition 1: Logical log fills to a high-watermark

Under two-phase commit, a participant database server that is waiting for instructions from the coordinator is blocked from completing its transaction. Because the transaction remains open, the logical-log files that contain records associated with this transaction cannot be freed. The result is that the logical log continues to fill because of the activity of concurrent users.

If the logical log fills to the value of the long-transaction high-watermark (LTXHWM) while the participant is waiting, the database server directs all database server threads that own long transactions to begin rolling them back. If a piece of work that is precommitted is the offending long transaction, the database server has initiated a heuristic rollback. That is, this database server is rolling back a precommitted piece of work without the instruction or knowledge of the coordinator.

Under two-phase commit, the logical-log files that contain records associated with the piece of work are considered open until an ENDTRANS logical-log record is written. This type of transaction differs from a transaction involving a single database server where a rollback actually closes the transaction.

The logical log might continue to fill until the exclusive high-watermark is reached (LTXEHWM). If this happens, all user threads are suspended except those that are currently rolling back or currently committing. In the two-phase commit scenario, the open transaction prevents you from backing up the logical-log files and freeing space in the logical log. Under these specific circumstances, the logical log can fill completely. If this happens, the participant database server shuts down, and you must perform a data restore.


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