Oracle 12c / SQL：“插入表a（从表b的x位置选择）”是否使用临时表？

Question

We are wondering why our temp space is always reducing temporarily but a lot (and released again). The command in question has the form

insert into table a (fields) select fields from table b where condition

Does Oracle use a temp table for commands like these? Manuals say "temp tables are only used for sorting", but we don't used a "order by" clause here.

Answer 1

TEMP tablespace is also used for other operations such as "direct path read" and as overflow for PGA memory intensive operations.

dba_hist_active_sess_history.temp_space_allocated (11g+) - shows SQL with high TEMP consumption

dba_hist_tbspc_space_usage - shows periods of high temp consumption

DBA_HIST_ACTIVE_SESS_HISTORY.pga_allocated can be used to show which SQL use the most PGA.