[jira] [Created] (CASSANDRA-5850) change gc_grace_seconds default to 28 days

["Robert Coli (JIRA)" <ji...@apache.org>]

Robert Coli created CASSANDRA-5850:
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             Summary: change gc_grace_seconds default to 28 days
                 Key: CASSANDRA-5850
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5850
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
    Affects Versions: 2.0 beta 2
            Reporter: Robert Coli
            Priority: Trivial


Current default for gc_grace_seconds is 10 days. Attached patch changes all instances of this 10 day default to 28 days. 

Rationale :

- 10 days is arbitrary, there is nothing special about the current value
- human societies do not operate on cycles which are a multiple of 10 days, they operate on a cycle of 7 day weeks
- operators must run repair once every gc_grace_seconds, and with typical data sizes (and compaction/streaming throttling) this might run for a significant fraction of 10 days
- repair often fails, and detecting and working around that failure might also take a significant fraction of 10 days
- repair is the heaviest operation one can run on a cassandra cluster and operators are therefore motivated to run it ~3x less frequently by default
- the worst case impact is keeping data around for 18 days longer than the previous default, and this only occurs in CFs which actually take DELETE operation
- 28 days is an even multiple of 7 days and easily comprehensible as a default time in which to schedule repair

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