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From Redmumba <redmu...@gmail.com>
Subject Re: Customized Compaction Strategy: Dev Questions
Date Wed, 04 Jun 2014 17:35:50 GMT
Let's say I run a major compaction every day, so that the "oldest" sstable
contains only the data for January 1st.  Assuming all the nodes are in-sync
and have had at least one repair run before the table is dropped (so that
all information for that time period is "the same"), wouldn't it be safe to
assume that the same data would be dropped on all nodes?  There might be a
period when the compaction is running where different nodes might have an
inconsistent view of just that days' data (in that some would have it and
others would not), but the cluster would still function and become
eventually consistent, correct?

Also, if the entirety of the sstable is being dropped, wouldn't the
tombstones be removed with it?  I wouldn't be concerned with individual
rows and columns, and this is a write-only table, more or less--the only
deletes that occur in the current system are to delete the old data.


On Wed, Jun 4, 2014 at 10:24 AM, Russell Bradberry <rbradberry@gmail.com>
wrote:

> I’m not sure what you want to do is feasible.  At a high level I can see
> you running into issues with RF etc.  The SSTables node to node are not
> identical, so if you drop a full SSTable on one node there is no one
> corresponding SSTable on the adjacent nodes to drop.    You would need to
> choose data to compact out, and ensure it is removed on all replicas as
> well.  But if your problem is that you’re low on disk space then you
> probably won’t be able to write out a new SSTable with the older
> information compacted out. Also, there is more to an SSTable than just
> data, the SSTable could have tombstones and other relics that haven’t been
> cleaned up from nodes coming or going.
>
>
>
>
> On June 4, 2014 at 1:10:58 PM, Redmumba (redmumba@gmail.com) wrote:
>
>  Thanks, Russell--yes, a similar concept, just applied to sstables.  I'm
> assuming this would require changes to both major compactions, and probably
> GC (to remove the old tables), but since I'm not super-familiar with the C*
> internals, I wanted to make sure it was feasible with the current toolset
> before I actually dived in and started tinkering.
>
> Andrew
>
>
> On Wed, Jun 4, 2014 at 10:04 AM, Russell Bradberry <rbradberry@gmail.com>
> wrote:
>
>>  hmm, I see. So something similar to Capped Collections in MongoDB.
>>
>>
>>
>> On June 4, 2014 at 1:03:46 PM, Redmumba (redmumba@gmail.com) wrote:
>>
>>   Not quite; if I'm at say 90% disk usage, I'd like to drop the oldest
>> sstable rather than simply run out of space.
>>
>> The problem with using TTLs is that I have to try and guess how much data
>> is being put in--since this is auditing data, the usage can vary wildly
>> depending on time of year, verbosity of auditing, etc..  I'd like to
>> maximize the disk space--not optimize the cleanup process.
>>
>> Andrew
>>
>>
>> On Wed, Jun 4, 2014 at 9:47 AM, Russell Bradberry <rbradberry@gmail.com>
>> wrote:
>>
>>>  You mean this:
>>>
>>>  https://issues.apache.org/jira/browse/CASSANDRA-5228
>>>
>>>  ?
>>>
>>>
>>>
>>> On June 4, 2014 at 12:42:33 PM, Redmumba (redmumba@gmail.com) wrote:
>>>
>>>   Good morning!
>>>
>>> I've asked (and seen other people ask) about the ability to drop old
>>> sstables, basically creating a FIFO-like clean-up process.  Since we're
>>> using Cassandra as an auditing system, this is particularly appealing to us
>>> because it means we can maximize the amount of auditing data we can keep
>>> while still allowing Cassandra to clear old data automatically.
>>>
>>> My idea is this: perform compaction based on the range of dates
>>> available in the sstable (or just metadata about when it was created).  For
>>> example, a major compaction could create a combined sstable per day--so
>>> that, say, 60 days of data after a major compaction would contain 60
>>> sstables.
>>>
>>> My question then is, will this be possible by simply implementing a
>>> separate AbstractCompactionStrategy?  Does this sound feasilble at all?
>>> Based on the implementation of Size and Leveled strategies, it looks like I
>>> would have the ability to control what and how things get compacted, but I
>>> wanted to verify before putting time into it.
>>>
>>> Thank you so much for your time!
>>>
>>> Andrew
>>>
>>>
>>
>

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