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From Flavio Baronti <f.baro...@list-group.com>
Subject Re: Time series data and deletion
Date Mon, 11 Mar 2013 16:25:50 GMT
Il 2013/03/11 14:42 PM, aaron morton ha scritto:
>> I'm trying to understand what will happen when we start deleting the old data.
> Are you going to delete data or use the TTL?
We delete the data explicitly, since we might change idea on the data TTL after it has been
written.
>
>> With size tiered compaction, suppose we have one 160Gb sstable and some smaller tables
totalling 40Gb.
> Not sure on that, it depends on the work load.
NVM, was just a hypothesis.
>
>>  My understanding is that, even if we start deleting, we will have to wait for 3
more 160Gb tables to appear, in 
>> order to have the first sstable compacted and the disk space freed. 
> v1.2 will run compactions on single SSTables that have a high number of tombstones
> https://issues.apache.org/jira/browse/CASSANDRA-3442
> https://issues.apache.org/jira/browse/CASSANDRA-4234
I did not know about these improvements in 1.2! We're still on 1.0.12, I'll push for an upgrade.

One more question. I read and reread your description of deletes [1],  but I still am confused
on tombstones and 
GCGraceSeconds, specifically when you say "If the deletion is before gcBefore it is totally
ignored".
Suppose I delete something, but compaction between the tombstone and the deleted data does
not happen within 
GCGraceSeconds. From what I understood, it looks like the tombstone will be ignored, and the
data will "resurrect"... 
where am I wrong?

Cheers
Flavio

[1] http://thelastpickle.com/2011/05/15/Deletes-and-Tombstones/#local_reads_for_local_queries

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