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https://issues.apache.org/jira/browse/CASSANDRA-14496?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16502045#comment-16502045
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Jon Haddad commented on CASSANDRA-14496:
----------------------------------------

I'm not a fan of enabling them by default.  There's no value for the frequency 
that make any sense at all given that a TTL could either be 5 minutes or 5 
years.   

If someone supplies the {{tombstone_compaction_interval}} I suppose it wouldn't 
be unreasonable to enable them.

> TWCS erroneously disabling tombstone compactions
> ------------------------------------------------
>
>                 Key: CASSANDRA-14496
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-14496
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Compaction
>            Reporter: Robert Tarrall
>            Priority: Minor
>
> This code:
> {code:java}
> this.options = new TimeWindowCompactionStrategyOptions(options);
> if 
> (!options.containsKey(AbstractCompactionStrategy.TOMBSTONE_COMPACTION_INTERVAL_OPTION)
>  && 
> !options.containsKey(AbstractCompactionStrategy.TOMBSTONE_THRESHOLD_OPTION))
> {
> disableTombstoneCompactions = true;
> logger.debug("Disabling tombstone compactions for TWCS");
> }
> else
> logger.debug("Enabling tombstone compactions for TWCS");
> }
> {code}
> ... in TimeWindowCompactionStrategy.java disables tombstone compactions in 
> TWCS if you have not *explicitly* set either tombstone_compaction_interval or 
> tombstone_threshold.  Adding 'tombstone_compaction_interval': '86400' to the 
> compaction stanza in a table definition has the (to me unexpected) side 
> effect of enabling tombstone compactions. 
> This is surprising and does not appear to be mentioned in the docs.
> I would suggest that tombstone compactions should be run unless these options 
> are both set to 0.
> If the concern is that (as with DTCS in CASSANDRA-9234) we don't want to 
> waste time on tombstone compactions when we expect the tables to eventually 
> be expired away, perhaps we should also check unchecked_tombstone_compaction 
> and still enable tombstone compactions if that's set to true.
> May also make sense to set defaults for interval & threshold to 0 & disable 
> if they're nonzero so that setting non-default values, rather than setting 
> ANY value, is what determines whether tombstone compactions are enabled?



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