This paragraph probably refers to the fact that Key/Values may be combined using a sub-set of the files for a tablet.
If you have 5 files, and 3 of them are being merged in a compaction, you won't see the keys from the other two files. When you are doing a scan, you will see all the entries. -Eric On Wed, Jul 15, 2015 at 5:15 AM, [email protected] < [email protected]> wrote: > Hi all, > > > > I’m implementing a range of combiners and my assumption is that at scan > time we will only have one single combined value returned (regardless of > whether the versioning iterator is applied), however the documentation in > the iterator_design.txt document isn’t clear whether that assumption is > correct: > > > > > > *A second consideration is that a Combiner is not guaranteed to see every > Key-Value pair* > > *which differ only by timestamp every time it is invoked. For example, if > there are 5 Key-Value* > > *pairs in a table which only differ by the timestamps 1, 2, 3, 4, and 5, > it is not guaranteed that* > > *every invocation of the Combiner will see 5 timestamps. One invocation > might see the Values for* > > *Keys with timestamp 1 and 4, while another invocation might see the > Values for Keys with the* > > > > *timestamps 1, 2, 4 and 5.* > > > > > > Is the above an implementation detail that we need to consider when > writing combiners, but not for the client implementation? Will the client > only have one value returned to it? > > Equally does the same statement above stay true for other forms of > iterators that are not combiners? > > > > Many thanks, > > > > Michael > > > > > > > *Michael Griffiths Developer BAE Systems Applied Intelligence * > *___________________________________________________________ * > *E: *[email protected] > > BAE Systems Applied Intelligence, Surrey Research Park, Guildford, Surrey, > GU2 7RQ. > www.baesystems.com/ai > > > Please consider the environment before printing this email. This message > should be regarded as confidential. If you have received this email in > error please notify the sender and destroy it immediately. Statements of > intent shall only become binding when confirmed in hard copy by an > authorised signatory. The contents of this email may relate to dealings > with other companies under the control of BAE Systems Applied Intelligence > Limited, details of which can be found at > http://www.baesystems.com/Businesses/index.htm. >
