[CASSANDRA-16253] Fix documentation to reflect real defaults for commit logs

• Type: Task
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 3.11.9, 4.0-beta4, 4.0
• Component/s: Documentation/Website
• Change Category: Semantic
• Complexity: Normal
• Platform: All

Source Control Link

https://github.com/apache/cassandra/commit/73a90b987dddedf6a13101c7d90114da669f52f5

Test and Documentation Plan

website previewing

• Assignee: Michael Semb Wever
• Reporter: Alain RODRIGUEZ

Authors

Michael Semb Wever

Reviewers

Michael Semb Wever

• Created: 09/Nov/20 10:11
• Updated: 03/Jan/21 16:58
• Resolved: 09/Nov/20 20:55

Description

About the documentation on commit logs:

• Commit logs default is every 10 sec - periodic, not batch https://github.com/apache/cassandra/blob/cassandra-3.11.8/conf/cassandra.yaml#L385-L386 (same in 3.11.9 or trunk). It can lead to data losses but still makes sense to me because fsync-ing every write is very expensive, and (even in batches) should be reserved for the super paranoid where handling multiple power-out (or sudden disk failures) simultaneously on multiple nodes needs to be handled (as mck explained to me).

  * Nonetheless, apart from the theory behind it, in a more practical perspective, the doc is wrong and says Default Value: batch which mislead me and this could happen to more people: https://cassandra.apache.org/doc/latest/architecture/storage_engine.html#commit-log

 

I think this is important enough for us to quickly fix the documentation in trunk. As this information is fully missing in the 3.11 branch documentation, I suggest we add it as well on that branch (based on information about commit logs from trunk).