SHOW POOL_CACHE displays in memory query cache statistics if in memory query cache is enabled. Here is an example session:
test=# \x \x Expanded display is on. test=# show pool_cache; show pool_cache; -[ RECORD 1 ]---------------+--------- num_cache_hits | 891703 num_selects | 99995 cache_hit_ratio | 0.90 num_hash_entries | 131072 used_hash_entries | 99992 num_cache_entries | 99992 used_cache_enrties_size | 12482600 free_cache_entries_size | 54626264 fragment_cache_entries_size | 0