[jira] [Commented] (KAFKA-15481) Concurrency bug in RemoteIndexCache leads to IOException

["Arpit Goyal (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-15481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17770830#comment-17770830 ] 

Arpit Goyal commented on KAFKA-15481:
-------------------------------------

[~divijvaidya]  [~showuon] 
1\ we want to ensure here is that removing the entry from cache and renaming the file to add "delete" suffix should be atomic operations OR
2\ we can add a UUID at the end of each index file downloaded from remote for this cache so that each "entry" in the cache has a unique file associated with it.
Should we go with the first or the 2nd approach , IMO 2nd would decouple the flow and would be simple to understand ?

> Concurrency bug in RemoteIndexCache leads to IOException
> --------------------------------------------------------
>
>                 Key: KAFKA-15481
>                 URL: https://issues.apache.org/jira/browse/KAFKA-15481
>             Project: Kafka
>          Issue Type: Bug
>    Affects Versions: 3.6.0
>            Reporter: Divij Vaidya
>            Priority: Major
>             Fix For: 3.7.0
>
>
> RemoteIndexCache has a concurrency bug which leads to IOException while fetching data from remote tier.
> Below events in order of timeline -
> Thread 1 (cache thread): invalidates the entry, removalListener is invoked async, so the files have not been renamed to "deleted" suffix yet.
> Thread 2: (fetch thread): tries to find entry in cache, doesn't find it because it has been removed by 1, fetches the entry from S3, writes it to existing file (using replace existing)
> Thread 1: async removalListener is invoked, acquires a lock on old entry (which has been removed from cache), it renames the file to "deleted" and starts deleting it
> Thread 2: Tries to create in-memory/mmapped index, but doesn't find the file and hence, creates a new file of size 2GB in AbstractIndex constructor. JVM returns an error as it won't allow creation of 2GB random access file.
> *Potential Fix*
> Use EvictionListener instead of RemovalListener in Caffeine cache as per the documentation:
> {quote} When the operation must be performed synchronously with eviction, use {{Caffeine.evictionListener(RemovalListener)}} instead. This listener will only be notified when {{RemovalCause.wasEvicted()}} is true. For an explicit removal, {{Cache.asMap()}} offers compute methods that are performed atomically.{quote}
> This will ensure that removal from cache and marking the file with delete suffix is synchronously done, hence the above race condition will not occur.



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