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https://issues.apache.org/jira/browse/CASSANDRA-8371?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14224390#comment-14224390
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Björn Hegerfors commented on CASSANDRA-8371:
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Could you try with a lower base_time_seconds? I have a feeling that I set the
default too high at 1 hour. That's a setting that I didn't actually benchmark
in my testing, and I just set it rather arbitrarily. You also need to make sure
the timestamp_resolution is set correctly.
You should think of base_time_seconds as DTCS's equivalent of min_sstable_size
in STCS. min_sstable_size is 50 MB by default, so you probably want to set
base_time_seconds to whatever time it takes you to write 50 MB, on average. I
suspect that will be a lot less than 1 hour. You could also try STCS with
min_sstable_size set to the amount that you write in an hour, to see if that
starts compacting equally much.
If that's the cause here, I think that we should consider lowering the default
value of base_time_seconds. Having it too low is better than too high. Does
anyone have an estimate of a common (on the high end) MB/s write throughput for
time series?
> 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
> Assignee: Björn Hegerfors
> Labels: compaction, performance
> 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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