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_entries_size | 12482600
free_cache_entries_size | 54626264
fragment_cache_entries_size | 0
Note: If the cache storage is memcached, values for all columns except num_cache_hits, num_selects and cache_hit_ratio show 0.