Termination-and-Recovery

Termination-and-Recovery - Termination and Recovery...

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Unformatted text preview: Termination and Recovery MESSAGES RECEIVED SITE 1 SITE 2 SITE 3 SITE 4 SITE 4 initial state committable non non non non Round 1 (1) CNNN-NNNN-NNNN-NNNN Round 2 FAILED (1)-CNNN--NNN--NNN Round 3 FAILED FAILED (1)--CNN---NN Round 4 FAILED FAILED FAILED (1)---CN Round 5 FAILED FAILED FAILED FAILED----C NOTE: (1) site fails after sending a single message Figure 5.4. Worst case execution of the resilient termination protocol Termination and Recovery The second issue can lead to very subtle problems. Again, consider the scenario where Site 1 sends a committable message to Site 2 and then crashes. Site 2 sends out non- committable messages, receives the committable message from Site 1, commits, and then promptly fails. Now, Site 3 receives a single non-committable message (from Site 2). Let us assume that Site 3 was not aware that Site 1 was up at the beginning of the protocol (a reasonable assumption). Then, Site 3 would not suspect that messages it received were inconsistent with those received by Site 2, and it would make an inconsistent commit decision 2 . Termination and Recovery Aborted On the other hand, it is always safe to commit the...
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Termination-and-Recovery - Termination and Recovery...

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