[jira] [Assigned] (KAFKA-19967) Reduce GC pressure in tiered storage read path by using direct memory buffers

["Nandini Singhal (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-19967?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Nandini Singhal reassigned KAFKA-19967:
---------------------------------------

    Assignee: Nandini Singhal

> Reduce GC pressure in tiered storage read path by using direct memory buffers
> -----------------------------------------------------------------------------
>
>                 Key: KAFKA-19967
>                 URL: https://issues.apache.org/jira/browse/KAFKA-19967
>             Project: Kafka
>          Issue Type: Improvement
>          Components: Tiered-Storage
>            Reporter: Nandini Singhal
>            Assignee: Nandini Singhal
>            Priority: Major
>
> Large heap buffer allocations in the tiered storage read path cause significant GC pressure by creating "humongous" objects that bypass young generation and go directly to old generation. Using direct buffers for these I/O-centric allocations would eliminate this GC overhead.
> (RemoteLogManager.java:1718):
> {code:java}
>   int updatedFetchSize = remoteStorageFetchInfo.minOneMessage() && firstBatchSize > maxBytes
>       ? firstBatchSize
>       : maxBytes;
>   ByteBuffer buffer = ByteBuffer.allocate(updatedFetchSize);{code}
>   Where maxBytes = Math.min(fetchMaxBytes, fetchInfo.maxBytes), which can be configured up to 55MB or
>   more depending on:
>   - replica.fetch.max.bytes (default: 1MB)
>   - replica.fetch.response.max.bytes (default: 10MB)
>   - Client-side max.partition.fetch.bytes
>  
> In the G1GC collector (Kafka's default), objects larger than half a region size (~32MB with 64MB regions) are considered "humongous" and:
>   1. Skip eden and young generation entirely
>   2. Allocated directly in old generation
>   3. Can only be reclaimed during expensive full/mixed GCs
>   4. Trigger old GCs more frequently
>   Example: With a 4GB heap and InitiatingHeapOccupancyPercent=35, approximately 25 concurrent tiered storage fetch requests (25 × 55MB = 1.375GB) would trigger an old GC. Under high read load from tiered storage, this creates continuous GC pressure.
>  



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