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Posted to commits@cassandra.apache.org by "Yifan Cai (Jira)" <ji...@apache.org> on 2019/11/11 06:56:00 UTC
[jira] [Commented] (CASSANDRA-15350) Add CAS “uncertainty” and “contention" messages that are currently propagated as a WriteTimeoutException.
[ https://issues.apache.org/jira/browse/CASSANDRA-15350?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16971341#comment-16971341 ]
Yifan Cai commented on CASSANDRA-15350:
---------------------------------------
The change of calculating the exact size of UTF-8 string has negative performance impact. It needs to iterate through the entire string to determine the actual size in UTF-8.
The benchmark setup and the result:
{code:java}
[java] Benchmark Mode Cnt Score Error Units
[java] Utf8StringEncodeBench.writeLongText avgt 6 552.458 ± 9.141 ns/op
[java] Utf8StringEncodeBench.writeLongTextWithExactSize avgt 6 787.676 ± 120.057 ns/op
[java] Utf8StringEncodeBench.writeShortText avgt 6 70.311 ± 8.031 ns/op
[java] Utf8StringEncodeBench.writeShortTextWithExactSize avgt 6 71.716 ± 4.790 ns/op
{code}
I will revert the change.
> Add CAS “uncertainty” and “contention" messages that are currently propagated as a WriteTimeoutException.
> ---------------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-15350
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15350
> Project: Cassandra
> Issue Type: Improvement
> Components: Feature/Lightweight Transactions
> Reporter: Alex Petrov
> Assignee: Yifan Cai
> Priority: Normal
> Labels: protocolv5, pull-request-available
> Attachments: Utf8StringEncodeBench.java
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> Right now, CAS uncertainty introduced in https://issues.apache.org/jira/browse/CASSANDRA-6013 is propagating as WriteTimeout. One of this conditions it manifests is when there’s at least one acceptor that has accepted the value, which means that this value _may_ still get accepted during the later round, despite the proposer failure. Similar problem happens with CAS contention, which is also indistinguishable from the “regular” timeout, even though it is visible in metrics correctly.
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