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