The correct format is:
ALTER TABLE snpSearch WITH compaction={'class':'SizeTieredCompactionStrategy'};
The format for WITH
options of the ALTER
command is described here. The important part is:
[...] The supported (and syntax) are the same as for the CREATE TABLE statement [...]
And the example from the CQL3.1 documentation shows how the compaction and compression strategies can be set.
( Tested on [cqlsh 4.0.1 | Cassandra 2.0.1 | CQL spec 3.1.1 | Thrift protocol 19.37.0]
.)