Safe Commits

When One Rollback Ripples

A read from an uncommitted writer can make a later rollback ripple to the reader.

highlighted = computed this step

When one rollback ripples

A rollback can ripple when another transaction has already read the rolled-back writer's value.

read before writer commit\text{read before writer commit}

Show the risky read

The diagram marks the read before the writer commits. That is the concrete action behind the cascading-abort risk.

uncommitted read\text{uncommitted read}

Safe commit and rollback schedules are tiny finite histories; logging, undo, ARIES, timing, isolation-level, product, and performance claims are out of scope.

Cascading abort riskeventtxopitemvalue1T1wX102T2rX3T1a4T2a reads-from factsreadEventreaderitemwriterwriteEventvalue2T2XT1110 external read dependencieswriterreaderitemwriteEventreadEventT1T2X12 classificationsfactvaluerecoverableyescascadelessnostrictno violationsnkindtx/readerwriteritem1cascadelessT2T1X2strictT2T1X

Read the safety label

The cascadeless classification is no, with 1 cascadeless violation.

cascadeless=no\text{cascadeless}=no

Summary

The model marks the risk from the read timing; it does not model undo or logging.

no recovery mechanism modeled\text{no recovery mechanism modeled}