> In another test, I increased the table records number, found the logical > reads is much larger than its block number. ... > There are just 96 blocks under hwm, while I got 3893 logical reads. That depends on how many rows each time client fetches from server. Default in SQLPlus is 15. So 57009/15 =~3800. Add 96 total block and you get 3896 which is almost the same 3893 consistent gets. see below (non relevant info skipped): SQL> exec dbms_stats.gather_table_stats(user, 'IOTEST'); PL/SQL procedure successfully completed. SQL> select blocks from user_tables where table_Name ='IOTEST'; BLOCKS ---------- 20 SQL> select count(*) from iotest; COUNT(*) ---------- 12667 SQL> set arraysize 15 SQL> set autot traceonly stat SQL> select * from iotest; 12667 rows selected. Statistics ---------------------------------------------------------- 868 consistent gets 846 SQL*Net roundtrips to/from client SQL> set arraysize 150 SQL> select * from iotest; 12667 rows selected. Statistics --------------------------------------------------- 108 consistent gets 86 SQL*Net roundtrips to/from client Gints Plivna http://www.gplivna.eu -- //www.freelists.org/webpage/oracle-l