Oralce line positioning and rowid:
drop table t purge;
create table t as select * from dba_objects;
create index idx_object_id on t(object_id);
set linesize 1000
set autotrace traceonly
- Method 1 (full table scan)
select /*+full(t)*/ * from t where object_id=2;
- Method 2 (index scan)
select * from t where object_id=2;
- Method 3 (rowid scanning)
set autotrace off
select rowid from t where object_id=2;
set autotrace traceonly
select * from t where object_id=2 and rowid='AAAYiZAALAAAADLAAw';
SQL> select /*+full(t)*/ * from t where object_id=2;
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 207 | 291 (1)| 00:00:04 |
|* 1 | TABLE ACCESS FULL| T | 1 | 207 | 291 (1)| 00:00:04 |
--------------------------------------------------------------------------
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
1044 consistent gets
SQL> select * from t where object_id=2;
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 207 | 2 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| T | 1 | 207 | 2 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IDX_OBJECT_ID | 1 | | 1 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
4 consistent gets
SQL> select * from t where object_id=2 and rowid='AAAYiZAALAAAADLAAw';
-----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 219 | 1 (0)| 00:00:01 |
|* 1 | TABLE ACCESS BY USER ROWID| T | 1 | 219 | 1 (0)| 00:00:01 |
-----------------------------------------------------------------------------------
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
1 consistent gets
--- start block size is 2K new tablespace (only 2K, 4K under WINDOWS, 8K and 16K
alter system set db_2k_cache_size=100M;
drop tablespace tbs_ljb_2k including contents and datafiles;
create tablespace TBS_LJB_2k
blocksize 2K
datafile 'D:\ORACLE\ORADATA\TEST11G\TBS_LJB_2K_01.DBF' size 100M
autoextend on
extent management local
segment space management auto;
create table t_2k tablespace tbs_ljb_2k as select * from dba_objects;
--- start block size is 4K new tablespace
alter system set db_4k_cache_size=100M;
drop tablespace tbs_ljb_4k including contents and datafiles;
create tablespace TBS_LJB_4k
blocksize 4K
datafile 'D:\ORACLE\ORADATA\TEST11G\TBS_LJB_4K_01.DBF' size 100M
autoextend on
extent management local
segment space management auto;
create table t_4k tablespace tbs_ljb_4k as select * from dba_objects;
--- Start of block sizes of 8K New Table space (default is 8K)
drop table t_8k purge;
create table t_8k as select * from dba_objects;
--- start block size of 16K new tablespace
alter system set db_16k_cache_size=100M;
drop tablespace tbs_ljb_16k including contents and datafiles;
create tablespace TBS_LJB_16k
blocksize 16K
datafile 'D:\ORACLE\ORADATA\TEST11G\TBS_LJB_16K_01.DBF' size 100M
autoextend on
extent management local
segment space management auto;
create table t_16k tablespace tbs_ljb_16k as select * from dba_objects;
-----------------------------------------------------------------------------------------
- Start the test and found that costs and fewer logical reads all this!
SET autotrace traceonly
select count(*) from t_2k;
/
select count(*) from t_4k;
/
select count(*) from t_8k;
/
select count(*) from t_16k;
/
- but it is not block the bigger the better, pay attention to the hot block competition.
SQL> select count(*) from t_2k;
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 891 (1)| 00:00:11 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| T_2K | 83292 | 891 (1)| 00:00:11 |
-------------------------------------------------------------------
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
4511 consistent gets
SQL> select count(*) from t_4k;
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 480 (1)| 00:00:06 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| T_4K | 63139 | 480 (1)| 00:00:06 |
-------------------------------------------------------------------
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
2137 consistent gets
SQL> select count(*) from t_8k;
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 291 (1)| 00:00:04 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| T_8K | 62320 | 291 (1)| 00:00:04 |
-------------------------------------------------------------------
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
1043 consistent gets
SQL> select count(*) from t_16k;
--------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 200 (1)| 00:00:03 |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | TABLE ACCESS FULL| T_16K | 80144 | 200 (1)| 00:00:03 |
--------------------------------------------------------------------
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
517 consistent gets
- Oracle system block size view
sqlplus "/ as sysdba"
show parameter db_block_size
select block_size
from dba_tablespaces
where tablespace_name='SYSTEM';
--- start a new block of size 2K tablespace (only 2K under WINDOWS, 4K, 8K and 16K)
alter system set db_2k_cache_size=100M;
drop tablespace tbs_ljb_2k including contents and datafiles;
create tablespace TBS_LJB_2k
blocksize 2K
datafile 'D:\ORACLE\ORADATA\TEST11G\TBS_LJB_2K_01.DBF' size 100M
autoextend on
extent management local
segment space management auto;
create table t_2k tablespace tbs_ljb_2k as select * from dba_objects where rownum<=100;
--- start block size is 4K new tablespace
alter system set db_4k_cache_size=100M;
drop tablespace tbs_ljb_4k including contents and datafiles;
create tablespace TBS_LJB_4k
blocksize 4K
datafile 'D:\ORACLE\ORADATA\TEST11G\TBS_LJB_4K_01.DBF' size 100M
autoextend on
extent management local
segment space management auto;
create table t_4k tablespace tbs_ljb_4k as select * from dba_objects where rownum<=100;
--- Start of block sizes of 8K New Table space (default is 8K)
drop table t_8k purge;
create table t_8k as select * from dba_objects where rownum<=100;
--- start block size of 16K new tablespace
alter system set db_16k_cache_size=100M;
drop tablespace tbs_ljb_16k including contents and datafiles;
create tablespace TBS_LJB_16k
blocksize 16K
datafile 'D:\ORACLE\ORADATA\TEST11G\TBS_LJB_16K_01.DBF' size 100M
autoextend on
extent management local
segment space management auto;
create table t_16k tablespace tbs_ljb_16k as select * from dba_objects where rownum<=100;
- The larger the block before tried, the less logical reads, but the reality is not block the bigger the better, but also pay attention to the hot block competition.
-------------------------------------------------------------------------------------------------------------------------------------------
sqlplus "/ as sysdba"
grant all on DBMS_LOCK to ljb;
connect ljb/ljb
- create a package to construct various JOB, analyze problems
create or replace package pkg_test_block_size
as
procedure p_t_2k;
procedure p_t_4k;
procedure p_t_8k;
procedure p_t_16k;
procedure p_exec_2k_job;
procedure p_exec_4k_job;
procedure p_exec_8k_job;
procedure p_exec_16k_job;
procedure p_remove_job;
end pkg_test_block_size;
/
create or replace package body pkg_test_block_size
as
procedure p_t_2k as
begin
for j in 1..1000 loop
for i in (select * from t_2k ) loop
null;
end loop;
end loop;
end p_t_2k;
procedure p_t_4k as
begin
for j in 1..1000 loop
for i in (select * from t_4k ) loop
null;
end loop;
end loop;
end p_t_4k;
procedure p_t_8k as
begin
for j in 1..1000 loop
for i in (select * from t_8k ) loop
null;
end loop;
end loop;
end p_t_8k;
procedure p_t_16k as
begin
for j in 1..1000 loop
for i in (select * from t_16k ) loop
null;
end loop;
end loop;
end p_t_16k;
- Create JOB
procedure p_exec_2k_job as
JOBNO NUMBER;
BEGIN
for i in 1..100 loop
DBMS_JOB.SUBMIT( JOBNO,
'pkg_test_block_size.p_t_2k;',
SYSDATE,
'SYSDATE+1/1440');
end loop;
DBMS_LOCK.sleep(120);
END p_exec_2k_job;
procedure p_exec_4k_job as
JOBNO NUMBER;
BEGIN
for i in 1..100 loop
DBMS_JOB.SUBMIT( JOBNO,
'pkg_test_block_size.p_t_4k;',
SYSDATE,
'SYSDATE+1/1440');
end loop;
DBMS_LOCK.sleep(120);
END p_exec_4k_job;
procedure p_exec_8k_job as
JOBNO NUMBER;
BEGIN
for i in 1..100 loop
DBMS_JOB.SUBMIT( JOBNO,
'pkg_test_block_size.p_t_8k;',
SYSDATE,
'SYSDATE+1/1440');
end loop;
DBMS_LOCK.sleep(120);
END p_exec_8k_job;
procedure p_exec_16k_job as
JOBNO NUMBER;
BEGIN
for i in 1..100 loop
DBMS_JOB.SUBMIT( JOBNO,
'pkg_test_block_size.p_t_16k;',
SYSDATE,
'SYSDATE+1/1440');
end loop;
DBMS_LOCK.sleep(120);
END p_exec_16k_job;
procedure p_remove_job as
BEGIN
for i in (select job from user_jobs )loop
DBMS_JOB.remove(i.job);
end loop;
END p_remove_job;
END pkg_test_block_size;
drop table test_latch purge;
create table test_latch (block_size varchar2(10),id number,gets number , misses number, sleeps number, immediate_gets number);
- Test 1.
delete from test_latch where block_size='2k';
insert into test_latch select '2k',1,gets,misses,sleeps,immediate_gets from v$latch where name='cache buffers chains';
commit;
--exec dbms_workload_repository.create_snapshot();
exec pkg_test_block_size.p_exec_2k_job;
--exec dbms_workload_repository.create_snapshot();
insert into test_latch select '2k',2,gets,misses,sleeps,immediate_gets from v$latch where name='cache buffers chains';
commit;
- end of the test
exec pkg_test_block_size.p_remove_job;
--@?/rdbms/admin/awrrpt.sql
- Test 2.
delete from test_latch where block_size='4k';
insert into test_latch select '4k',1,gets,misses,sleeps,immediate_gets from v$latch where name='cache buffers chains';
commit;
--exec dbms_workload_repository.create_snapshot();
exec pkg_test_block_size.p_exec_4k_job;
--exec dbms_workload_repository.create_snapshot();
insert into test_latch select '4k',2,gets,misses,sleeps,immediate_gets from v$latch where name='cache buffers chains';
commit;
- end of the test
exec pkg_test_block_size.p_remove_job;
--@?/rdbms/admin/awrrpt.sql
- Test 3.
delete from test_latch where block_size='8k';
insert into test_latch select '8k',1,gets,misses,sleeps,immediate_gets from v$latch where name='cache buffers chains';
commit;
--exec dbms_workload_repository.create_snapshot();
exec pkg_test_block_size.p_exec_8k_job;
--exec dbms_workload_repository.create_snapshot();
insert into test_latch select '8k',2,gets,misses,sleeps,immediate_gets from v$latch where name='cache buffers chains';
commit;
- end of the test
exec pkg_test_block_size.p_remove_job;
--@?/rdbms/admin/awrrpt.sql
- Test 4.
delete from test_latch where block_size='16k';
insert into test_latch select '16k',1,gets,misses,sleeps,immediate_gets from v$latch where name='cache buffers chains';
commit;
--exec dbms_workload_repository.create_snapshot();
exec pkg_test_block_size.p_exec_16k_job;
--exec dbms_workload_repository.create_snapshot();
insert into test_latch select '16k',2,gets,misses,sleeps,immediate_gets from v$latch where name='cache buffers chains';
commit;
- end of the test
exec pkg_test_block_size.p_remove_job;
--@?/rdbms/admin/awrrpt.sql
SELECT WHAT, INTERVAL, JOB, NEXT_DATE, NEXT_SEC, FAILURES, BROKEN FROM USER_JOBS WHERE INTERVAL = 'SYSDATE+1/1440';
select * from v$latch_children where name='cache buffers chains'
select * from test_latch;
- The following results are for reference only, actual implementation may be due to the amount of data is not large enough, concurrency is not big enough, but there are differences.
select block_size,
misses - lag_misses
from (select t.*,lag(misses) over(partition by block_size order by misses) lag_misses
from test_latch t) k
where k.lag_misses is not null;
BLOCK_SIZE MISSES-LAG_MISSES
---------- ------------------
2k 0
4k 47 407
8K 67769
16k 86871
Observed:
select t.*, s.sid, s.serial#, s.machine, s.program, s.osuser
from (select c.USERNAME,
a.event,
a.cnt as "TIME(SECOND)",
a.sql_id,
b.sql_fulltext
from (select rownum rn, t.*
from (select decode(s.session_state,
'WAITING',
s.event,
'Cpu + Wait For Cpu') Event,
s.sql_id,
s.user_id,
count(*) CNT
from v$active_session_history s
where sample_time > sysdate - 15 / 1440
group by s.user_id,
decode(s.session_state,
'WAITING',
s.event,
'Cpu + Wait For Cpu'),
s.sql_id
order by CNT desc) t
where rownum < 20) a,
v$sqlarea b,
dba_users c
where a.sql_id = b.sql_id
and a.user_id = c.user_id
order by CNT desc) t,
v$session s
where t.sql_id = s.sql_id(+);