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From: Aaron Turner <synfinatic@gmail.com>
Date: Sat, 11 Aug 2012 11:55:50 -0700
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Subject: Re: quick question about data layout on disk
To: user@cassandra.apache.org
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Thanks Russell, that's the info I was looking for!

On Sat, Aug 11, 2012 at 11:23 AM, Russell Haering
<russellhaering@gmail.com> wrote:
> Your update doesn't go directly to an sstable (which are immutable),
> it is first merged to an in-memory table. Eventually the memtable is
> flushed to a new sstable.
>
> See http://wiki.apache.org/cassandra/MemtableSSTable
>
> On Sat, Aug 11, 2012 at 11:03 AM, Aaron Turner <synfinatic@gmail.com> wrote:
>> So how does that work?  An sstable is for a single CF, but it can and
>> likely will have multiple rows.  There is no read to write and as I
>> understand it, writes are append operations.
>>
>> So if you have an sstable with say 26 different rows (A-Z) already in
>> it with a bunch of columns and you add a new column to row J, how does
>> Cassandra store the column/value pair on disk in a way to refer to row
>> J without re-writing the row key or some representation of it?
>>
>> Thanks,
>> Aaron
>>
>> On Fri, Aug 10, 2012 at 7:53 PM, Terje Marthinussen
>> <tmarthinussen@gmail.com> wrote:
>>> Rowkey is stored only once in any sstable file.
>>>
>>> That is, in the spesial case where you get sstable file per column/value, you are correct, but normally, I guess most of us are storing more per key.
>>>
>>> Regards,
>>> Terje
>>>
>>> On 11 Aug 2012, at 10:34, Aaron Turner <synfinatic@gmail.com> wrote:
>>>
>>>> Curious, but does cassandra store the rowkey along with every
>>>> column/value pair on disk (pre-compaction) like Hbase does?  If so
>>>> (which makes the most sense), I assume that's something that is
>>>> optimized during compaction?
>>>>
>>>>
>>>> --
>>>> Aaron Turner
>>>> http://synfin.net/         Twitter: @synfinatic
>>>> http://tcpreplay.synfin.net/ - Pcap editing and replay tools for Unix & Windows
>>>> Those who would give up essential Liberty, to purchase a little temporary
>>>> Safety, deserve neither Liberty nor Safety.
>>>>    -- Benjamin Franklin
>>>> "carpe diem quam minimum credula postero"
>>
>>
>>
>> --
>> Aaron Turner
>> http://synfin.net/         Twitter: @synfinatic
>> http://tcpreplay.synfin.net/ - Pcap editing and replay tools for Unix & Windows
>> Those who would give up essential Liberty, to purchase a little temporary
>> Safety, deserve neither Liberty nor Safety.
>>     -- Benjamin Franklin
>> "carpe diem quam minimum credula postero"


-- 
Aaron Turner
http://synfin.net/         Twitter: @synfinatic
http://tcpreplay.synfin.net/ - Pcap editing and replay tools for Unix & Windows
Those who would give up essential Liberty, to purchase a little temporary
Safety, deserve neither Liberty nor Safety.
    -- Benjamin Franklin
"carpe diem quam minimum credula postero"