I want to know how to verify disk hits by a `select` query in PostgreSQL 9.4 on CentOS 6.5. Also please let me know how far enabling the `log_statement_stats` in the `postgresql.conf` will help me. 

I need to understand the 'filesystem blocks in/out' value in the logs when I switch the above parameter to `on`.

For example, please check the log snippet:

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    2016-02-03 14:12:45 PST LOG:  statement: select * from test_stats_collect ;
    2016-02-03 14:12:45 PST LOG:  QUERY STATISTICS
    2016-02-03 14:12:45 PST DETAIL:  ! system usage stats:
            !       0.069489 elapsed 0.027995 user 0.002999 system sec
            !       [0.131979 user 0.146977 sys total]
            !       0/0 [3280/26440] filesystem blocks in/out
            !       0/5 [19/4866] page faults/reclaims, 0 [0] swaps
            !       0 [0] signals rcvd, 0/0 [0/0] messages rcvd/sent
            !       20/116 [125/174] voluntary/involuntary context switches