Create a new RocksDB batch every 32k records.
Create a new RocksDB batch every 32k records.

This unfortunately breaks atomicity but it will hopefully stop us
running out of memory when huge numbers are records are loaded in
a single request.

nla/tinycdxserver,nla/outbackcdx,nla/tinycdxserver,nla/tinycdxserver,nla/outbackcdx,nla/outbackcdx,nla/outbackcdx,nla/tinycdxserver