There's some rationale here: http://mail-archives.apache.org/mod_mbox/cassandra-user/201305.mbox/%3CCAENxBwx6pcSA=cWn=dKW_52K5odw5F3Xigj-zn_4BwFth+4ruA@mail.gmail.com%3E
And I'm sure part of the reason is the 64k size limit: maps (and sets and lists) are limited to 64k total size (http://wiki.apache.org/cassandra/CassandraLimitations), so it wouldn't be very read-efficient to load individual elements.
On 10/28/2013 08:03 PM, Liam Stewart wrote:
I was wondering if anybody could explain the rationale behind disallowing selection of individual elements from a map in CQL and why an entire map must be retrieved at once when items are stored as distinct columns? Are there any plans to allow individual selection?
Liam Stewart :: firstname.lastname@example.org