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From "Marcus Eriksson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6654) Droppable tombstones are not being removed from LCS table despite being above 20%
Date Thu, 27 Feb 2014 19:41:19 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6654?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13914958#comment-13914958
] 

Marcus Eriksson commented on CASSANDRA-6654:
--------------------------------------------

Yes, it is intended, we cannot drop tombstones if they might cover live data in other sstables.

It has improved a lot in 2.1 though, but iirc the change was quite complicated so backporting
to 2.0 was not an option.

bq. For the use case targeted by Keith Wright would the best workaround is to stick with the
implied forever TTL on most columns (don't specify one) and just set TTL for these shorter
lived values?

I think splitting up the data and keeping data with different life times in different tables
might be a better way here.

Another workaround I've seen before is using STCS and scheduling weekly major compactions,
that will get rid of all tombstones.

> Droppable tombstones are not being removed from LCS table despite being above 20%
> ---------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-6654
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6654
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>         Environment: 1.2.13 VNodes with murmur3
>            Reporter: Keith Wright
>            Assignee: Marcus Eriksson
>         Attachments: Screen Shot 2014-02-05 at 9.38.20 AM.png, dtrlog.txt, repro3.py
>
>
> JMX is showing that one of our CQL3 LCS tables has a droppable tombstone ratio above
20% and increasing (currently at 28%).  Compactions are not falling behind and we are using
the OOTB setting for this feature so I would expect not to go above 20% (will attach screen
shot from JMX).   Table description:
> CREATE TABLE global_user (
>   user_id timeuuid,
>   app_id int,
>   type text,
>   name text,
>   extra_param map<text, text>,
>   last timestamp,
>   paid boolean,
>   sku_time map<text, timestamp>,
>   values map<timestamp, float>,
>   PRIMARY KEY (user_id, app_id, type, name)
> ) WITH
>   bloom_filter_fp_chance=0.100000 AND
>   caching='KEYS_ONLY' AND
>   comment='' AND
>   dclocal_read_repair_chance=0.000000 AND
>   gc_grace_seconds=86400 AND
>   read_repair_chance=0.100000 AND
>   replicate_on_write='true' AND
>   populate_io_cache_on_flush='false' AND
>   compaction={'sstable_size_in_mb': '160', 'class': 'LeveledCompactionStrategy'} AND
>   compression={'chunk_length_kb': '8', 'crc_check_chance': '0.1', 'sstable_compression':
'LZ4Compressor'}; 



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