FWIW: I (@rondy) am not the creator of the content shared here, which is an excerpt from Edmond Lau's book. I simply copied and pasted it from another location and saved it as a personal note, before it gained popularity on news.ycombinator.com. Unfortunately, I cannot recall the exact origin of the original source, nor was I able to find the author's name, so I am can't provide the appropriate credits.
| ** Find commmonly accessed tables and their use of indexes: | |
| SELECT relname,seq_tup_read,idx_tup_fetch,cast(idx_tup_fetch AS numeric) / (idx_tup_fetch + seq_tup_read) AS idx_tup_pct FROM pg_stat_user_tables WHERE (idx_tup_fetch + seq_tup_read)>0 ORDER BY idx_tup_pct; | |
| Returns output like: | |
| relname | seq_tup_read | idx_tup_fetch | idx_tup_pct | |
| ----------------------+--------------+---------------+------------------------ | |
| schema_migrations | 817 | 0 | 0.00000000000000000000 | |
| user_device_photos | 349 | 0 | 0.00000000000000000000 |
L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns
Compress 1K bytes with Zippy ............. 3,000 ns = 3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns = 20 µs
SSD random read ........................ 150,000 ns = 150 µs
Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs