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https://issues.apache.org/jira/browse/RATIS-2350?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18048495#comment-18048495
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Tsz-wo Sze commented on RATIS-2350:
-----------------------------------
bq. However, if Read 1 and Read 2 return different colors, ...
Since we have strong consistency and both two reads start after the two writes,
it won't return different color.
bq. Therefore, I'm not sure whether the strong "read-after-write" consistency
is also linearizable.
Yes, read-after-write is a part of linearizable read. It is a part of the
readIndex algorithm.
- See
https://github.com/apache/ratis/blob/6e1e15f0f54aba0795a1d704a967e70275033e87/ratis-server/src/main/java/org/apache/ratis/server/impl/LeaderStateImpl.java#L1142-L1149
We cannot enable read-after-write without linearizable read.
> Fix readAfterWrite bugs
> -----------------------
>
> Key: RATIS-2350
> URL: https://issues.apache.org/jira/browse/RATIS-2350
> Project: Ratis
> Issue Type: Bug
> Components: server
> Reporter: Tsz-wo Sze
> Assignee: Tsz-wo Sze
> Priority: Major
> Fix For: 3.3.0
>
> Attachments: image-2025-12-31-10-28-28-475.png, screenshot-1.png,
> screenshot-2.png
>
> Time Spent: 1.5h
> Remaining Estimate: 0h
>
> There are bugs in handling readAfterWrite requests:
> # In LeaderStateImpl.getReadIndex(..), it should use the max of
> readAfterWriteConsistentIndex and commitIndex.
> # In WriteIndexCache.add(..), it should combine the current future with
> previous future when the previous future exists.
> Improvement:
> - Add lastAppliedIndex to ReadIndexQueue
> - Replace Consumer<Long> with LongConsumer
> Bug in tests:
> - In LinearizableReadTests.runTestReadAfterWrite(..), it tries to assert the
> following:
> {quote}Assertion: _read-after-write is more consistent than linearizable read_
> {quote}
> Recall the definitions:
> {quote}Read-after-write: _Within the same client, the read called after write
> must able to see the change of the write._
> {quote}
> {quote}Linearizable read: _The read is linearizable (i.e. it won't read stale
> data)._
> {quote}
> Suppose readIndex is 9 and writeIndex is 10. By definition, read-after-write
> must return any state at log index A >= 10 while linearizable read must
> return any state at log index L >= 9. The assertion incorrectly check if A >=
> L, which is not a requirement. It is perfectly fine, for example, if A=11 <
> L=12.
> ----
> Original Summary: TestReadOnlyRequestWithGrpc may fail intermittently
> Original Description:
> {code:java}
> org.apache.ratis.grpc.TestReadOnlyRequestWithGrpc.testReadAfterWrite -- Time
> elapsed: 1.572 s <<< FAILURE!
> org.opentest4j.AssertionFailedError: expected: <true> but was: <false>
> at
> org.apache.ratis.ReadOnlyRequestTests.testReadAfterWriteImpl(ReadOnlyRequestTests.java:314)
> at
> org.apache.ratis.server.impl.MiniRaftCluster$Factory$Get.runWithNewCluster(MiniRaftCluster.java:143)
> at
> org.apache.ratis.server.impl.MiniRaftCluster$Factory$Get.runWithNewCluster(MiniRaftCluster.java:121)
> at
> org.apache.ratis.ReadOnlyRequestTests.testReadAfterWrite(ReadOnlyRequestTests.java:289)
> {code}
> It failed 8 in [this 10x10
> run|https://github.com/apache/ratis/actions/runs/19023405871/job/54322726144].
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