db_block_checking与db_block_checksum
sys@OMREP> show parameter db_block_checkNAME 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
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