cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Alain RODRIGUEZ <arodr...@gmail.com>
Subject Re: how to immediately delete tombstones
Date Thu, 31 May 2018 18:02:32 GMT
Hello,

It's a very common but somewhat complex topic. We wrote about it 2 years
ago and I really think this post might have answers you are looking for:
http://thelastpickle.com/blog/2016/07/27/about-deletes-and-tombstones.html

Something that you could try (if you do care ending up with one big sstable
:)) is to enable 'unchecked_tombstone_compaction'. This removes a pre-check
supposed to only trigger tombstone compactions when it is worth it (ie
there is no sstable overlaps) but that over time proved to be inefficient
from a tombstone eviction perspective.

If data can actually be deleted (no overlaps, gc_grace_seconds lowered or
reached, ...) then changing option 'unchecked_tombstone_compaction' to
'true' might do a lot of good in terms of disk space. Be aware that a bunch
of compactions might be triggered and that disk space will start by
increasing before (possibly) reducing after the compactions.

The gc_grace of table was default (10 days), now i set that to 0, although
> many compactions finished but no space reclaimed so far.
>

Be aware that if some deletes did not reach all the replicas, the data will
eventually come back as lowering the gc_grace_seconds, you don't allow
repairs to process the data before tombstones are actually evicted.

Also, by setting the gc_grace_seconds to 0, you also disabled the hints
altogether. gc_grace_seconds should always be equivalent to
'max_hint_windows_in_ms'. My colleague Radovan wrote a post with
more information on this:
http://thelastpickle.com/blog/2018/03/21/hinted-handoff-gc-grace-demystified.html

Good luck with your tombstones, again, those are a bit tricky to handle
sometimes ;-)

C*heers,
-----------------------
Alain Rodriguez - @arodream - alain@thelastpickle.com
France / Spain

The Last Pickle - Apache Cassandra Consulting
http://www.thelastpickle.com

2018-05-31 16:19 GMT+01:00 Nicolas Guyomar <nicolas.guyomar@gmail.com>:

> Hi,
>
> You need to manually force compaction if you do not care ending up with
> one big sstable (nodetool compact)
>
> On 31 May 2018 at 11:07, onmstester onmstester <onmstester@zoho.com>
> wrote:
>
>> Hi,
>> I've deleted 50% of my data row by row now disk usage of cassandra data
>> is more than 80%.
>> The gc_grace of table was default (10 days), now i set that to 0,
>> although many compactions finished but no space reclaimed so far.
>> How could i force deletion of tombstones in sstables and reclaim the disk
>> used by deleted rows?
>> I'm using cassandra on a single node.
>>
>> Sent using Zoho Mail <https://www.zoho.com/mail/>
>>
>>
>>
>

Mime
View raw message