073eee46_n_Memory_Columnar_Store__IMCS___Recommendations
[Parameter name] imcs.shmem_size [Description] Size of shared memory (Mb) used by columnar store. [Default value] 8*1024 (8Gb) [Recommendations] 
Make it large enough to fit all data requiring vertical representation. It can not be increased without restart of the server.
In-Memory Columnar Store (IMCS)
Recommendations