Re: Logical IO

From: Gints Plivna <>
Date: Wed, 18 Nov 2009 11:31:39 +0200
Message-ID: <>

> 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';



SQL> select count(*) from iotest;



SQL> set arraysize 15
SQL> set autot traceonly stat
SQL> select * from iotest;

12667 rows selected.


        868  consistent gets
        846  SQL*Net roundtrips to/from client

SQL> set arraysize 150
SQL> select * from iotest;

12667 rows selected.


        108  consistent gets
         86  SQL*Net roundtrips to/from client

Gints Plivna

Received on Wed Nov 18 2009 - 03:31:39 CST

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