Some background on the read and write paths, some of the extra details are a little out of date but mostly correct in 1.2
http://www.slideshare.net/aaronmorton/cassandra-community-webinar-introduction-to-apache-cassandra-12-20353118/40 http://thelastpickle.com/2011/04/28/Forces-of-Write-and-Read/ http://thelastpickle.com/2011/07/04/Cassandra-Query-Plans/ Cheers ----------------- Aaron Morton Cassandra Consultant New Zealand @aaronmorton http://www.thelastpickle.com On 7/08/2013, at 9:07 PM, Michał Michalski <mich...@opera.com> wrote: > I'm not sure how accurate it is (it's from 2011, one of its sources is from > 2010), but I'm pretty sure it's more or less OK: > > http://blog.csdn.net/firecoder/article/details/7019435 > > M. > > W dniu 07.08.2013 10:34, Nikolay Mihaylov pisze: >> thanks >> >> It will use the Index Sample (RAM) first, then it will use "full" Index >> (disk) and finally it will read data from SSTable (disk). There's no such >> thing like "collision" in this case. >> >> so it still have 2 seeks :) >> >> where I can see the internal structure of the sstable i tried to find it >> documented but was unable to find anything ? >> >> >> >> >> On Wed, Aug 7, 2013 at 11:27 AM, Michał Michalski <mich...@opera.com> wrote: >> >>> >>> 2. when cassandra lookups a key in sstable (assuming bloom-filter and >>>> other >>>> "stuff" failed, also assuming the key is located in this single sstable), >>>> cassandra DO NOT USE sequential I/O. "She" probably will read the >>>> hash-table slot or similar structure, then cassandra will do another disk >>>> seek in order to get the value (and probably the key). Also probably there >>>> will need another seek, if there is key collision there will need >>>> additional seeks. >>>> >>> >>> It will use the Index Sample (RAM) first, then it will use "full" Index >>> (disk) and finally it will read data from SSTable (disk). There's no such >>> thing like "collision" in this case. >>> >>> >>> 3. once the data (e.g. the row) is located, a sequential read for entire >>>> row will occur. (Once again I assume there is single well compacted >>>> sstable). Also if disk is not fragmented, the data will be placed on disk >>>> sectors one after the other. >>>> >>> >>> Yes, this is how I understand it too. >>> >>> M. >>> >>> >> >
