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https://issues.apache.org/jira/browse/CASSANDRA-17401?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18045455#comment-18045455
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Alex Petrov edited comment on CASSANDRA-17401 at 12/16/25 1:12 PM:
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I have looked around, and it looks like we rely on having both statements
during upgrades to check if statements are cached correctly (perhaps we need to
add a corresponding comment).
I think we can still make it work though. I think we should just use
{{preparedStatements.invalidateAll()}} instead of regular {{invalidate}}.
Unfortunately we will be able to somehow synchronize deletes from stable
storage, but I think this is fine, we can allow races there, since they're not
correctness-impacting. Eventually we will save both statements with correct
hashes.
Another addition to the patch I would do is adding an if statement when
retrieving {{cachedWithKeyspace}} after {{cachedWithoutKeyspace}}, and only
going for a second {{get}} if hashes are actually different.
LMK if this approach still fixes the issue for you.
was (Author: ifesdjeen):
I have looked around, and it _seems_ to be safe to remove eviction.
The only addition to the patch I would do is adding an if statement when
retrieving {{cachedWithKeyspace}} after {{cachedWithoutKeyspace}}, and only
going for a second {{get}} if hashes are actually different.
+1 other than that, assuming all prepared statement-related tests pass.
> Race condition in QueryProcessor causes just prepared statement not to be in
> the prepared statements cache
> ----------------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-17401
> URL: https://issues.apache.org/jira/browse/CASSANDRA-17401
> Project: Apache Cassandra
> Issue Type: Bug
> Components: Messaging/Client
> Reporter: Ivan Senic
> Assignee: Jaydeepkumar Chovatia
> Priority: Normal
> Time Spent: 10m
> Remaining Estimate: 0h
>
> The changes in the
> [QueryProcessor#prepare|https://github.com/apache/cassandra/blame/cassandra-4.0.2/src/java/org/apache/cassandra/cql3/QueryProcessor.java#L575-L638]
> method that were introduced in versions *4.0.2* and *3.11.12* can cause a
> race condition between two threads trying to concurrently prepare the same
> statement. This race condition can cause removing of a prepared statement
> from the cache, after one of the threads has received the result of the
> prepare and eventually uses MD5Digest to call
> [QueryProcessor#getPrepared|https://github.com/apache/cassandra/blame/cassandra-4.0.2/src/java/org/apache/cassandra/cql3/QueryProcessor.java#L212-L215].
> The race condition looks like this:
> * Thread1 enters _prepare_ method and resolves _safeToReturnCached_ as false
> * Thread1 executes eviction of hashes
> * Thread2 enters _prepare_ method and resolves _safeToReturnCached_ as false
> * Thread1 prepares the statement and caches it
> * Thread1 returns the result of the prepare
> * Thread2 executes eviction of hashes
> * Thread1 tries to execute the prepared statement with the received
> MD5Digest, but statement is not in the cache as it was evicted by Thread2
> I tried to reproduce this by using a Java driver, but hitting this case from
> a client side is highly unlikely and I can not simulate the needed race
> condition. However, we can easily reproduce this in Stargate (details
> [here|https://github.com/stargate/stargate/pull/1647]), as it's closer to
> QueryProcessor.
> Reproducing this in a unit test is fairly easy. I am happy to showcase this
> if needed.
> Note that the issue can occur only when safeToReturnCached is resolved as
> false.
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