[CASSANDRA-14496] TWCS erroneously disabling tombstone compactions when unchecked_tombstone_compaction=true

• Type: Bug
• Status: Resolved
• Priority: Low
• Resolution: Fixed
• Fix Version/s: 3.11.11, 4.0.1, 4.1-alpha1, 4.1
• Component/s: Local/Compaction
• Severity: Low
• Since Version: NA

Source Control Link

https://github.com/apache/cassandra/commit/fd9a2820a1ceb1812fce4f4cc71abc0324d5908f

• Assignee: Alexander Ivakov
• Reporter: Robert Tarrall

Authors

Alexander Ivakov, Brandon Williams

Reviewers

Marcus Eriksson

• Created: 05/Jun/18 00:21
• Updated: 27/May/22 19:25
• Resolved: 02/Jul/21 18:52

Description

This code:

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");
}

... 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?