[CASSANDRA-16071] max_compaction_flush_memory_in_mb is interpreted as bytes

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 3.11.8, 3.11.10, 4.0-beta2, 4.0-beta4, 4.0
• Component/s: Feature/SASI
• Bug Category: Correctness - API / Semantic Implementation
• Severity: Normal
• Complexity: Normal
• Discovered By: User Report
• Platform: All
• Since Version: 3.4

Source Control Link

https://github.com/apache/cassandra/commit/116e9c1678a1e96748236962e71319f337e07f8d

Test and Documentation Plan

CI run. Unit test added.

• Assignee: Michael Semb Wever
• Reporter: Michael Semb Wever

Authors

Michael Semb Wever

Reviewers

Zhao Yang

• Created: 24/Aug/20 09:39
• Updated: 05/Dec/20 17:52
• Resolved: 25/Aug/20 18:24

Description

In CASSANDRA-12662, scottcarey reported that the max_compaction_flush_memory_in_mb setting gets incorrectly interpreted in bytes rather than megabytes as its name implies.

1. the setting 'max_compaction_flush_memory_in_mb' is a misnomer, it is actually memory in BYTES. If you take it at face value, and set it to say, '512' thinking that means 512MB, you will produce a million temp files rather quickly in a large compaction, which will exhaust even large values of max_map_count rapidly, and get the OOM: Map Error issue above and possibly have a very difficult situation to get a cluster back into a place where nodes aren't crashing while initilaizing or soon after. This issue is minor if you know about it in advance and set the value IN BYTES.

Issue Links

• relates to: CASSANDRA-12662 OOM when using SASI index