o get historical information on what SQL statements are incurring the most disk reads

SELECT * FROM ( SELECT sql_id, sum(disk_reads_delta) disk_reads_delta,

sum(disk_reads_total) disk_reads_total, sum(executions_delta) execs_delta, sum(executions_total) execs_total

FROM dba_hist_sqlstat GROUP BY sql_id ORDER BY 2 desc)

WHERE rownum <= 5;