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https://issues.apache.org/jira/browse/CASSANDRA-16996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17421078#comment-17421078
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Caleb Rackliffe commented on CASSANDRA-16996:
---------------------------------------------
Linking my comments from
[here|https://issues.apache.org/jira/browse/CASSANDRA-16856?focusedCommentId=17420953&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-17420953].
To expand on that a bit, I think we need at least 2 and possibly 3 things here,
if it's clear that the problem identified in CASSANDRA-16856 is legitimate (and
I think it is) and we want to make schema modifications atomic for
{{SchemaKeyspace}}:
1.) To protect {{saveSystemKeyspacesSchema()}}, {{truncate()}},
{{calculateSchemaDigest()}}, {{convertSchemaToMutations()}}, and
{{applyChanges()}}, given those are the places we deal with the contents of the
entire schema keyspace.
2.) JavaDoc for {{SchemaKeyspace}} that explicitly lays out the class's
synchronization policy and why it is that way. (This might need to mention in
passing how this interacts w/ {{Schema}}, which also has its own
synchronization that sort of incompletely overlaps w/ {{SchemaKeyspace}}.)
3.) (perhaps optional, but really nice and maybe not optional) A fuzz test like
the one I mentioned
[here|https://issues.apache.org/jira/browse/CASSANDRA-16856?focusedCommentId=17420953&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-17420953]
to simulate the case we're worried about at a reasonable level. In this case,
it probably means hitting {{convertSchemaToMutations()}}, which is a good proxy
for {{SchemaPullVerbHandler#doVerb()}}, concurrent to schema changes and/or
truncations (possibly from {{Schema#transform()}}).
There is another way we might be able to solve this problem, and that's
delegating more of our schema manipulation to {{Schema}}, where we're already
synchronizing some of the codepaths that hit {{SchemaKeyspace}}. In that case,
we could just annotate the latter as being explicitly not thread-safe.
> Prevent broken concurrent schema read/writes
> --------------------------------------------
>
> Key: CASSANDRA-16996
> URL: https://issues.apache.org/jira/browse/CASSANDRA-16996
> Project: Cassandra
> Issue Type: Bug
> Components: Cluster/Schema
> Reporter: Berenguer Blasi
> Assignee: Berenguer Blasi
> Priority: Normal
> Fix For: 3.11.x, 4.0, 4.x
>
>
> See CASSANDRA-16856 where the concurrent read/write path was left out
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