You might want to take a look at `unchecked_tombstone_compaction` table setting. The best way to see if this is affecting you is to look at the sstablemetadata for the sstables and see if your tombstone ratio is higher than the configured tombstone_threshold ratio (0.2 be default) for the table.
For example the sstable has a tombstone_threshold of 0.2 but you see sstables OLDER than 10 days (LCS has a tombstone compaction interval of 10 days, it won't run a tombstone compaction until a sstable is at least 10 days old). > sstablemetadata example-ka-1233-Data.db | grep droppable Estimated droppable tombstones: 1.0 ^ this is an extreme example but anything greater than .2 on a 10+ day sstable is a problem. By default the unchecked_tombstone_compaction setting is false which will lead to tombstones staying around if a partition spans multiple sstables (which may happen with LCS over a long period). Try setting `unchecked_tombstone_compaction` to true, note: that when you first run this IF any sstables are above the tombstone_ratio setting for that table they will be compacted, this may cause extra load on the cluster. Vytenis ... always do your own research and verify what people say. :) On Mon, Jul 5, 2021 at 10:11 PM manish khandelwal < manishkhandelwa...@gmail.com> wrote: > Thanks Kane for the suggestion. > > Regards > Manish > > On Tue, Jul 6, 2021 at 6:19 AM Kane Wilson <k...@raft.so> wrote: > >> >> In one of our LCS table auto compaction was disabled. Now after years of >>> run, range queries using spark-cassandra-connector are failing. Cassandra >>> version is 2.1.16. >>> >>> I suspect due to disabling of autocompaction lots of tombstones got >>> created. And now while reading those are creating issues and queries are >>> getting timed out. Am I right in my thinking? What is the possible way to >>> get out of this? >>> >>> I thought of using major compaction but for LCS that was introduced in >>> Cassandra 2.2. Also user defined compactions dont work on LCS tables. >>> >>> >>> >>> Regards >>> >>> Manish Khandelwal >>> >> >> If it's tombstones specifically you'll be able to see errors in the logs >> regarding passing the tombstone limit. However, disabling compactions could >> cause lots of problems (especially over years). I wouldn't be surprised if >> your reads are slow purely because of the number of SSTables you're hitting >> on each read. Given you've been running without compactions for so long you >> might want to look at just switching to STCS and re-enabling compactions. >> Note this should be done with care, as it could cause performance/storage >> issues. >> >> Cheers, >> Kane >> >> -- >> raft.so - Cassandra consulting, support, and managed services >> >
