[jira] [Created] (CASSANDRA-8371) DateTieredCompactionStrategy is always compacting

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

mck created CASSANDRA-8371:
------------------------------

             Summary: DateTieredCompactionStrategy is always compacting 
                 Key: CASSANDRA-8371
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8371
             Project: Cassandra
          Issue Type: Bug
          Components: Core
            Reporter: mck
         Attachments: java_gc_counts_rate-month.png, read-latency.png, sstables.png, vg2_iad-month.png

Running 2.0.11 and having switched a table to [DTCS|https://issues.apache.org/jira/browse/CASSANDRA-6602] we've seen that disk IO and gc count increase, along with the number of reads happening in the "compaction" hump of cfhistograms.

Data, and generally performance, looks good, but compactions are always happening, and pending compactions are building up.

The schema for this is 
{code}CREATE TABLE search (
  loginid text,
  searchid timeuuid,
  description text,
  searchkey text,
  searchurl text,
  PRIMARY KEY ((loginid), searchid)
);{code}

We're sitting on about 82G (per replica) across 6 nodes in 4 DCs.
CQL executed against this keyspace, and traffic patterns, can be seen in slides 7+8 of https://prezi.com/b9-aj6p2esft

Attached are sstables-per-read and read-latency graphs from cfhistograms, and screenshots of our munin graphs as we have gone from STCS, to LCS (week ~44), to DTCS (week ~46).

These screenshots are also found in the prezi on slides 9-11.

[~pmcfadin], [~Bj0rn], 

Can this be a consequence of occasional deleted rows, as is described under (3) in the description of CASSANDRA-6602 ?




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