I have a top wait event of "direct path read", which shows Average Wait time (Avg wait (ms)) of 96ms (in the top 5 events section). However, in the "Tablespace IO Stats" section, the only active tablespace (USERS) shows that "Av Rd(ms)" is at 2ms. How could this be? Bug in the AWR report? - Or does Oracle somehow calculate the average wait for direct path reads in a different manner? - Anything else I should be looking at?
Top 5 Timed Foreground Events
Event Waits Time(s) Avg wait (ms) % DB time Wait Class
direct path read 64,753 6,219 96 72.51 User I/O
Tablespace IO Stats
ordered by IOs (Reads + Writes) desc
Tablespace Reads Av Reads/s Av Rd(ms) Av Blks/Rd Writes Av Writes/s Buffer Waits Av Buf Wt(ms)
USERS 234,653 61 1.59 61.38 94,687 25 12 20.83
UNDOTBS1 307 0 1.30 1.00 208,752 54 0 0.00
TEMP 10,279 3 0.10 14.99 10,276 3 0 0.00
A quick glance in the documentation shows that this wait might be misleading, as some I/O events are asynchronous. You can read more about it here - https://docs.oracle.com/cd/B16240_01/doc/doc.102/e16282/oracle_database_help/oracle_database_wait_bottlenecks_direct_path_read_pct.html