http://itknowledgeexchange.techtarget.com/itanswers Fri, 24 May 2013 17:54:18 +0000 en-US hourly 1 http://itknowledgeexchange.techtarget.com/itanswers/why-do-i-not-see-db-block-gets-and-consistent-gets/ http://itknowledgeexchange.techtarget.com/itanswers/why-do-i-not-see-db-block-gets-and-consistent-gets/#comments Wed, 13 Jul 2011 16:48:24 +0000 SAPORACLE hi,

i have two test scenarios where i’m trying to understand to actual concept of db block gets and consistent gets.

SQL> set autotrace on

SQL>select * from scott.emp;

i get 14 rows then

Execution Plan ———————————————————-    0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=3 Card=14 Bytes=51           8)

   1    0   TABLE ACCESS (FULL) OF ‘EMP’ (TABLE) (Cost=3 Card=14 Bytes           =518)

Statistics ———————————————————-        1528  recursive calls           0  db block gets         289  consistent gets          44  physical reads           0  redo size        1585  bytes sent via SQL*Net to client         522  bytes received via SQL*Net from client           4  SQL*Net roundtrips to/from client          31  sorts (memory)           0  sorts (disk)          14  rows processed

on the above i do not see db block gets why?

when i run the same statement again this is what i get

Execution Plan ———————————————————-    0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=3 Card=14 Bytes=51           8)

   1    0   TABLE ACCESS (FULL) OF ‘EMP’ (TABLE) (Cost=3 Card=14 Bytes           =518)

 

 

Statistics ———————————————————-           0  recursive calls           0  db block gets          10  consistent gets           0  physical reads           0  redo size        1585  bytes sent via SQL*Net to client         522  bytes received via SQL*Net from client           4  SQL*Net roundtrips to/from client           0  sorts (memory)           0  sorts (disk)          14  rows processed no db lock gets again why?

basically i want to understand the difference between db block gets and consisten gets

also i run the same statement from different session and i get below result

Execution Plan ———————————————————-    0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=3 Card=14 Bytes=51           8)

   1    0   TABLE ACCESS (FULL) OF ‘EMP’ (TABLE) (Cost=3 Card=14 Bytes           =518)

Statistics ———————————————————-           0  recursive calls           0  db block gets           0  consistent gets           0  physical reads           0  redo size           0  bytes sent via SQL*Net to client           0  bytes received via SQL*Net from client           0  SQL*Net roundtrips to/from client           0  sorts (memory)           0  sorts (disk)          14  rows processed

here i do not see anything, why?

please help me understand the what’s happening here?

any help would be greatly appreciated

thanks in advance

 

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