Because without AFFINITY KEY option we do not know order of fields within composite PK which is very important for index creation.
вт, 20 марта 2018 г. в 19:58, Dmitriy Setrakyan <dsetrak...@apache.org>: > On Tue, Mar 20, 2018 at 2:09 PM, Vladimir Ozerov <voze...@gridgain.com> > wrote: > >> Internally Ignite is key-value storage. It use key to derive partition it >> belongs to. By default the whole key is used. Alternatively you can use >> @AffinityKey annotation in cache API or "affinityKey" option in CREATE >> TABLE to specify *part of the key* to be used for affinity calculation. >> Affinity column cannot belong to value because in this case single >> key-value pair could migrate between nodes during updates and >> IgniteCache.get(K) will not be able to locate the key in cluster. >> > > Vladimir, while it makes sense that the key must be composed of the ID and > Affinity Key, I still do not understand why we require that user declares > them both as PRIMARY KEY. Why do you need to enforce that explicitly? In my > view you can do it automatically, if you see that the table has both, > PRIMARY KEY and AFFINITY KEY declared. > >
