[CASSANDRA-16436] Add startup check for large read_ahead_kb setting

• Type: Improvement
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 4.1-alpha1, 4.1
• Component/s: Local/Startup and Shutdown
• Labels: AdventCalendar2021 lhf
• Change Category: Operability
• Complexity: Low Hanging Fruit
• Platform: Linux

Source Control Link

https://github.com/apache/cassandra/commit/9b291f18abfc62ab45e725effe75a8ceb9163760

Test and Documentation Plan

https://github.com/apache/cassandra/pull/1354

• Assignee: Kanthi Subramanian Assign to me
• Reporter: Paulo Motta

Authors

Kanthi Subramanian

Reviewers

Brandon Williams, Paulo Motta

• Created: 09/Feb/21 19:06
• Updated: 27/May/22 19:25
• Resolved: 03/Jan/22 21:41

Description

A well known production tuning recommendation is to dial back the read_ahead_kb Linux setting from the default of 4096 in most distributions as this can cause high IO usage and cache churn on read-intensive workloads.

We should add a startup warning to detect when a high read_ahead_kb is used and recommend the user to dial back to a reasonable value, which varies according to the workload but a general guideline is to tune this to 8kb.

Issue Links

• relates to: CASSANDRA-17237 Pathological interaction between Cassandra and readahead, particularly on Centos 7 VMs