db_block_checking与db_block_checksum

湖北佛

sys@OMREP> show parameter db_block_check


NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_block_checking                    string      FALSE
db_block_checksum                    string      TYPICAL

sys@OMREP> create table test (col int) tablespace users;

sys@OMREP> set timing on

sys@OMREP> alter system set db_block_checksum=FALSE;  

sys@OMREP> !cat scott.sql
begin
for i in 1..&1 loop
        insert into test values(i);
end loop;
end;
/

sys@OMREP> @scott 100000
old   2: for i in 1..&1 loop
new   2: for i in 1..100000 loop

PL/SQL procedure successfully completed.

Elapsed: 00:00:03.83
sys@OMREP> commit;

Commit complete.

sys@OMREP> alter system set db_block_checking=TRUE;  

System altered.

sys@OMREP> alter system set db_block_checksum=TRUE;  

System altered.

sys@OMREP> @scott 100000
old   2: for i in 1..&1 loop
new   2: for i in 1..100000 loop

PL/SQL procedure successfully completed.

Elapsed: 00:00:14.69
sys@OMREP> commit;

Commit complete.

db_block_checking 是逻辑上判断，还判断内存内数据块
db_block_checksum 是物理上判断，
两个参数对system表空间不起作用，且消耗资源，和redo latch竞争，

system表空间用一下参数:
sys@OMREP> @ implicit
Enter value for name: _db_always_check
NAME                           VALUE    DESCRIB
------------------------------ -------- ----------------------------------------------------------------------
_db_always_check_system_ts     TRUE     Always perform block check and checksum for System tablespace

伙夫和甲鱼

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