Re: Logical IO

From: Gints Plivna <gints.plivna@xxxxxxxxx>
To: john.o.golden@xxxxxxxxx
Date: Wed, 18 Nov 2009 11:31:39 +0200

> 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
--
http://www.freelists.org/webpage/oracle-l

References:

Logical IO
From: John Glohahi

Re: Logical IO

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