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From Alexander Dejanovski <a...@thelastpickle.com>
Subject Re: need to reclaim space with TWCS
Date Sat, 20 Jan 2018 16:16:59 GMT
I would turn background read repair off on the table to improve the overlap
issue, but you'll still have foreground read repair if you use quorum reads
anyway.

So put dclocal_... to 0.0.

The commit you're referring to has been merged in 3.11.1 as 2.1 doesn't
patched anymore.

Le sam. 20 janv. 2018 à 16:55, Brian Spindler <brian.spindler@gmail.com> a
écrit :

> Hi Alexander, after re-reading this
> https://issues.apache.org/jira/browse/CASSANDRA-13418 it seems you would
> recommend leaving dclocal_read_repair at maybe 10%  is that true?
>
> Also, has this been patched to 2.1?
> https://github.com/thelastpickle/cassandra/commit/58440e707cd6490847a37dc8d76c150d3eb27aab#diff-e8e282423dcbf34d30a3578c8dec15cdR176
>
>
> Cheers,
>
> -B
>
>
> On Sat, Jan 20, 2018 at 10:49 AM Brian Spindler <brian.spindler@gmail.com>
> wrote:
>
>> Hi Alexander,  Thanks for your response!  I'll give it a shot.
>>
>> On Sat, Jan 20, 2018 at 10:22 AM Alexander Dejanovski <
>> alex@thelastpickle.com> wrote:
>>
>>> Hi Brian,
>>>
>>> You should definitely set unchecked_tombstone_compaction to true and set
>>> the interval to the default of 1 day. Use a tombstone_threshold of 0.6 for
>>> example and see how that works.
>>> Tombstones will get purged depending on your partitioning as their
>>> partition needs to be fully contained within a single sstable.
>>>
>>> Deleting the sstables by hand is theoretically possible but should be
>>> kept as a last resort option if you're running out of space.
>>>
>>> Cheers,
>>>
>>> Le sam. 20 janv. 2018 à 15:41, Brian Spindler <brian.spindler@gmail.com>
>>> a écrit :
>>>
>>>> I probably should have mentioned our setup: we’re on Cassandra version
>>>> 2.1.15.
>>>>
>>>>
>>>> On Sat, Jan 20, 2018 at 9:33 AM Brian Spindler <
>>>> brian.spindler@gmail.com> wrote:
>>>>
>>>>> Hi, I have several column families using TWCS and it’s great.
>>>>> Unfortunately we seem to have missed the great advice in Alex’s article
>>>>> here: http://thelastpickle.com/blog/2016/12/08/TWCS-part1.html about
>>>>> setting the appropriate aggressive tombstone settings and now we have
lots
>>>>> of timestamp overlaps and disk space to reclaim.
>>>>>
>>>>>
>>>>>
>>>>> I am trying to figure the best way out of this. Lots of the SSTables
>>>>> with overlapping timestamps in newer SSTables have droppable tombstones
at
>>>>> like 0.895143957 or something similar, very close to 0.90 where the full
>>>>> sstable will drop afaik.
>>>>>
>>>>>
>>>>>
>>>>> I’m thinking to do the following immediately:
>>>>>
>>>>>
>>>>>
>>>>> Set *unchecked_tombstone_compaction = true*
>>>>>
>>>>> Set* tombstone_compaction_interval == TTL + gc_grace_seconds*
>>>>>
>>>>> Set* dclocal_read_repair_chance = 0.0 (currently 0.1)*
>>>>>
>>>>>
>>>>>
>>>>> If I do this, can I expect TWCS/C* to reclaim the space from those
>>>>> SSTables with 0.89* droppable tombstones?   Or do I (can I?) manually
>>>>> delete these files and will c* just ignore the overlapping data and treat
>>>>> as tombstoned?
>>>>>
>>>>>
>>>>>
>>>>> What else should/could be done?
>>>>>
>>>>>
>>>>>
>>>>> Thank you in advance for your advice,
>>>>>
>>>>>
>>>>>
>>>>> *__________________________________________________*
>>>>>
>>>>> *Brian Spindler *
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>> --
>>> -----------------
>>> Alexander Dejanovski
>>> France
>>> @alexanderdeja
>>>
>>> Consultant
>>> Apache Cassandra Consulting
>>> http://www.thelastpickle.com
>>>
>> --
-----------------
Alexander Dejanovski
France
@alexanderdeja

Consultant
Apache Cassandra Consulting
http://www.thelastpickle.com

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