> 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?
> 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. > 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 > So although we need to store 200Gb worth of data, we'll need something like > 800Gb disk space in order to be on the safe side, right? You want to keep the disks below 75% capacity, and want to have free space to handle node moves etc. I do not think you need 800GB because of tombstones deletions. > What would happen instead with leveled compaction? Levelled compaction is more suited to workloads that have a high insert/delete ratio. In your case, write once read many data is will suited to Sized Tiered. Cheers ----------------- Aaron Morton Freelance Cassandra Consultant New Zealand @aaronmorton http://www.thelastpickle.com On 8/03/2013, at 9:13 AM, Flavio Baronti <f.baro...@list-group.com> wrote: > Hello, > > we are using Cassandra for storing time series data. We never update, only > append; we plan to store 1 year worth of data, occupying something around > 200Gb. I'm trying to understand what will happen when we start deleting the > old data. > > With size tiered compaction, suppose we have one 160Gb sstable and some > smaller tables totalling 40Gb. 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. So although we > need to store 200Gb worth of data, we'll need something like 800Gb disk space > in order to be on the safe side, right? > > What would happen instead with leveled compaction? And why is the default > sstable size so small (5Mb)? If we need to store 200Gb, this means we will > have 40k sstables; since each one makes 5 files, we'll have 200k files in a > single directory, which we'm afraid will undermine the stability of the file > system. > > Thank you for your suggestions! > > Flavio >
