[jira] [Commented] (CAMEL-22176) High CPU Usage and Deadlock/Race Condition (?) in SimpleLRUCache after Upgrade (>4.8.2)

["Claus Ibsen (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CAMEL-22176?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17981833#comment-17981833 ] 

Claus Ibsen commented on CAMEL-22176:
-------------------------------------

[~essobedo] just in case you read this. 

> High CPU Usage and Deadlock/Race Condition (?) in SimpleLRUCache after Upgrade (>4.8.2)
> ---------------------------------------------------------------------------------------
>
>                 Key: CAMEL-22176
>                 URL: https://issues.apache.org/jira/browse/CAMEL-22176
>             Project: Camel
>          Issue Type: Bug
>          Components: camel-core
>    Affects Versions: 4.8.3
>            Reporter: Andre
>            Priority: Major
>
> *Summary:*
> After upgrading Apache Camel to a version greater than 4.8.2, we are experiencing significant CPU usage spikes, potential deadlocks, or race conditions. The issue appears to be related to the changes introduced in CAMEL-21888, specifically affecting the {{compressChangesIfNeeded()}} method in {{{}SimpleLRUCache{}}}.
> *Environment:*
>  * Apache Camel version: 4.8.x (issue persists in 4.12.0)
>  * Previous working version: 4.8.2
>  * Large file processing: thousands of files from a file input to SFTP
>  * Cache size: 50,000
>  * Files processed per run: ~1,000
> *Description:*
> Following the upgrade, we observed that when processing large numbers of files (e.g., 1,000 files per run), the {{lastChanges}} queue in {{SimpleLRUCache}} fills up rapidly. For each file, the {{OperationContext}} is invoked, which clears and empties the queue. Since our workload rarely has duplicates, this results in a high number of iterations—potentially 50 million for 1,000 files and a 50,000 cache size.
> This behavior leads to:
>  * *High CPU usage* (sometimes reaching 100%)
>  * *Application startup delays or failures*
>  * *Potential deadlocks or race conditions* due to excessive locking or queue operations
> This appears to be a regression caused by the change in {{{}SimpleLRUCache.{}}}.
> *Steps to Reproduce:*
>  # Upgrade Camel to a version >4.8.2.
>  # Configure a route that processes thousands of files (e.g., from a directory to an SFTP endpoint).
>  # Set the cache size to a high value (e.g., 50,000).
>  # Observe CPU usage and application responsiveness during processing.
> *Expected Behavior:*
> Efficient cache management without excessive CPU usage or risk of deadlocks, even with large numbers of files and a high cache size.
> *Actual Behavior:*
>  * CPU usage spikes to 100% during processing.
>  * Application may fail to start or becomes unresponsive.
>  * Large number of iterations in {{compressChangesIfNeeded()}} due to the way {{lastChanges}} is managed.
> *Suspected Root Cause:*
> The change to use a {{Deque}} for {{lastChanges}} and the logic in {{compressChangesIfNeeded()}} is not efficient for high-throughput scenarios with large caches and frequent operations, especially when there are few or no duplicates
>  
> *Notes*
>  * We noticed regression in two independent services after upgrading camel - both with high indication that the LRUCache is the problem.
>  * After changing {{compressChangesIfNeeded()}} to {{noop}} the CPU usage and deadlock/race condition issues are gone



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