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https://issues.apache.org/jira/browse/CASSANDRA-19948?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17885572#comment-17885572
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Josh McKenzie commented on CASSANDRA-19948:
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Unless I'm misunderstanding your position, the failure scenario has nothing to
do with file durability in the commitlog. If you run a subset of replicas with
CDC, you're at risk of a QUORUM write not being available for CDC processing
should the one overlap you have (assuming RF=3) fail before CDC is processed.
* A: No CDC. Receives Write.
* B: CDC. Receives Write. Fails
* C: CDC. Does not receive write.
Data is on A and no CDC running to process it.
B is down and unavailable for CDC processing.
C has CDC processing enabled but doesn't see the write until anti-entropy runs,
and that's a whole other can of worms since that repair would have to still be
going through the write path, not zero-copy, etc.
> Changing cdc table property can cause schema disagreement
> ---------------------------------------------------------
>
> Key: CASSANDRA-19948
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19948
> Project: Cassandra
> Issue Type: Bug
> Components: Cluster/Schema
> Reporter: Bowen Song
> Priority: Normal
> Fix For: 4.1.x, 5.0.x, 5.x
>
> Attachments: 4.1.1.txt, 4.1.6.txt, 5.0.0-corrected.txt,
> cdc_schema_disagreement.sh
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> In the cassandra.yaml file, there is a parameter named "cdc_enabled" which
> allows CDC to be enabled or disabled on each individual nodes.
> It has been found that it can cause schema disagreement or discrepancy when
> an "ALTER TABLE ... WITH cdc=..." statement is ran against a node which has
> "cdc_enabled" set to "false" in a cluster in which nodes have mixed
> "true"/"false" values for the "cdc_enabled" settings.
> The exact behaviour of the above is version-dependant.
> On Cassandra 4.1.1, the cluster will end up in the schema disagreement state.
> A rolling restart will bring the schema back in sync, but the changes made to
> the `cdc` table property will be lost.
> On Cassandra 4.1.6, the cluster will not have visible schema disagreement in
> the "nodetool describecluster" command's output, but the "ALTER TABLE"
> statement only has cosmetic effect on the node it is run. The node with
> "cdc_enabled" set to "false" will show the "cdc" table property has changed,
> but this does not affect its behaviour in any way. At the same time, other
> nodes do not see that table property change at all. This is perhaps even
> worse than on 4.1.1, because the alter table statement is silently failing.
> On Casandra 5.0.0, the behaviour is the same as 4.1.6.
> A shell script for reproducing the above described behaviours in Docker, and
> the outputs of it on both 4.1.1 and 4.1.6 and 5.0.0 are attached.
>
> Edit on 25 Sep: added test result on 5.0.0
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