Ariel Weisberg created CASSANDRA-18276:
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Summary: Paxos read throws TimeoutException instead of retrying
when contending with writes when it could retry
Key: CASSANDRA-18276
URL: https://issues.apache.org/jira/browse/CASSANDRA-18276
Project: Cassandra
Issue Type: Bug
Components: Feature/Lightweight Transactions
Reporter: Ariel Weisberg
Assignee: Ariel Weisberg
[Paxos.read currently copies the code to throw timeout
exception|https://github.com/apache/cassandra/blob/ece0c4a44c9209dc64240f3f33ca7a57d7548daa/src/java/org/apache/cassandra/service/paxos/Paxos.java#L873]
if the read had side effects. This doesn’t make much sense because the empty
proposal doesn’t have a side effect so it should be safe to retry the empty
proposal instead of throwing timeout immediately.
The impact of this is a little more severe because it’s also [not waiting
during
propose|https://github.com/apache/cassandra/blob/ece0c4a44c9209dc64240f3f33ca7a57d7548daa/src/java/org/apache/cassandra/service/paxos/PaxosPropose.java#L166]
to see if there wouldn’t have been side effects for its empty proposal so it
will always think there were side effects and timeout immediately if there are
any refusals.
Of course this only ever happens when it thinks the read might not be
linearizable because it witnessed some in progress operation during the
prrepare/promise phase.
This should be pretty easy to fix either by removing the side effect immediate
timeout code entirely, or at least improved by actually waiting for side
effects during propose.
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