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Oracle Hints Tutorial for improving performance
 
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Oracle Hints Tutorial for improving performance APPEND PARALLEL JOIN INDEX NO_INDEX SELECT /*+ FIRST_ROWS(10) */ * FROM emp WHERE deptno = 10; SELECT /*+ ALL_ROWS */ * FROM emp WHERE deptno = 10; SELECT /*+ NO_INDEX(emp emp_dept_idx) */ * FROM emp, dept WHERE emp.deptno = dept.deptno; SELECT /*+ INDEX(e,emp_dept_idx) */ * FROM emp e WHERE e.deptno = 10; -- SELECT /*+ INDEX(scott.emp,emp_dept_idx) */ * FROM scott.emp; SELECT /*+ AND_EQUAL(e,emp_dept_idx) */ * FROM emp e; SELECT /*+ INDEX_JOIN(e,emp_dept_idx) */ * FROM emp e; SELECT /*+ PARALLEL_INDEX(e,emp_dept_idx , 8) */ * FROM emp e; SELECT /*+ LEADING (dept) */ * FROM emp, dept WHERE emp.deptno = dept.deptno; SELECT /*+ PARALLEL(8) CACHE (e) FULL (e) */ * FROM emp e ; SELECT /*+ PARALLEL FULL (e) */ * FROM emp e ; SELECT /*+ PARALLEL USE_MERGE (emp dept) */ * FROM emp, dept WHERE emp.deptno = dept.deptno; -- SORT Merge Join SELECT /*+ PARALLEL USE_HASH (emp dept) */ * FROM emp, dept WHERE emp.deptno = dept.deptno; -- Hash Join SELECT /*+ PARALLEL */ * FROM emp e ; INSERT /*+ APPEND */ INTO mytmp select /*+ CACHE (e) */ *from emp e; commit;
Views: 4872 TechLake
Why Use Parallel Processing?
 
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This video compares the use of parallel and serial processing for the same SQL query. Copyright © 2012 Oracle and/or its affiliates. Oracle® is a registered trademark of Oracle and/or its affiliates. All rights reserved. Oracle disclaims any warranties or representations as to the accuracy or completeness of this recording, demonstration, and/or written materials (the "Materials"). The Materials are provided "as is" without any warranty of any kind, either express or implied, including without limitation warranties of merchantability, fitness for a particular purpose, and non-infringement.
TABLESPACE MANAGEMENT READ ONLY READ WRITE LOGGING NOLOGGING OFFLINE ONLINE MODES
 
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How to put tablespace in read only, read write, logging , nologging, online, offline =================================================================================== alter tablespace king read only; (we can only read the data(select will work)) alter tablespace king read write; (we can read and write data) alter tablespace king logging; (changes will record in redolog) alter tablespace king nologging; (changes will not record in redolog) alter tablespace king online; (everyone can access) alter tablespace king offline; (can't access) select tablespace_name,status,logging from dba_tablespaces;
Views: 625 Praveen Biyyapu
How to Detect Soft Corruption in Oracle 12c Database
 
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Detection of Soft Corruption in 12c: To use the scripts below replace : , ",# and $ by proper bracket Lets Create a tablespace and small table. SQL: create tablespace DEMO1 datafile '/u02/tstdb1/TSTDB1/datafile/demo01.dbf' size 50M SQL: create table objects tablespace DEMO1 as select * from dba_objects; SQL: alter table objects add constraint pk_obj primary key #object_id$; SQL: create index idx_obj_name on objects#object_name$ tablespace demo1; Backup tablespace. RMAN: backup tablespace DEMO1; We need to put the DB in archivelog first Rebuild index with NOLOGGING option to simulate soft corruption later. RMAN: alter index idx_obj_name rebuild nologging; Confirm that we have datafiles that require backup because they have been affected with NOLOGGING operation. RMAN: report unrecoverable; Simulate corruption. RMAN: alter database datafile 5 offline; RMAN: restore datafile 5; RMAN: recover datafile 5; RMAN: alter database datafile 5 online; Query table with corrupted index and notice error. SQL: select count#*$ from objects where object_name like 'A%'; Let’s perform validation of datafile to check block corruption. RMAN: backup validate check logical datafile 5; Notice that we have 457 blocks marked corrupt but v$database_block_corruption view is empty. SQL: select count#*$ from v$database_block_corruption; Let’s query v$nonlogged_block view. set lines 200 set pages 999 select file#, block#, blocks,object#,reason from v$nonlogged_block; Will RMAN detect that we have corrupted blocks? RMAN: backup datafile 5; RMAN backup won’t fail due to NOLOGGING corrupt blocks and our backup will contain soft corrupted blocks. Let’s Identify corrupt segments using v$nonlogged_block view. set lines 2000 set pages 9999 col owner for a20 col partition_name for a10 col segment_name for a20 SELECT e.owner, e.segment_type, e.segment_name, e.partition_name, c.file# , greatest#e.block_id, c.block#$ corr_start_block# , least#e.block_id+e.blocks-1, c.block#+c.blocks-1$ corr_end_block# , least#e.block_id+e.blocks-1, c.block#+c.blocks-1$ - greatest#e.block_id, c.block#$ + 1 blocks_corrupted FROM dba_extents e, V$NONLOGGED_BLOCK c WHERE e.file_id = c.file# AND e.block_id "= c.block# + c.blocks - 1 AND e.block_id + e.blocks - 1 := c.block# UNION SELECT s.owner, s.segment_type, s.segment_name, s.partition_name, c.file# , header_block corr_start_block# , header_block corr_end_block# , 1 blocks_corrupted FROM dba_segments s, V$NONLOGGED_BLOCK c WHERE s.header_file = c.file# AND s.header_block between c.block# and c.block# + c.blocks - 1 UNION SELECT null owner, null segment_type, null segment_name, null partition_name, c.file# , greatest#f.block_id, c.block#$ corr_start_block# , least#f.block_id+f.blocks-1, c.block#+c.blocks-1$ corr_end_block# , least#f.block_id+f.blocks-1, c.block#+c.blocks-1$ - greatest#f.block_id, c.block#$ + 1 blocks_corrupted FROM dba_free_space f, V$NONLOGGED_BLOCK c WHERE f.file_id = c.file# AND f.block_id "= c.block# + c.blocks - 1 AND f.block_id + f.blocks - 1 := c.block# order by file#, corr_start_block# / This is the best outcome to get if you notice corruption errors. All errors are related to index corruption so we could fix this problem rebuilding index. alter index idx_obj_name rebuild; Simply issuing "alter index rebuild" command won't work. We should mark index unusable to drop segment before rebuilding it or just rebuild index with online option. It is better choice to mark index unusable because you don't need additional space then, but I will simply rebuild index with online option and see what will happen. SQL: alter index idx_obj_name rebuild online; Index altered. SQL: select count#*$ from objects where object_name like 'A%'; No errors... but, let's validate datafile for corruption. RMAN: backup validate check logical datafile 5; Notice "Marked Corrupt" column. Hm... 457 like before. Don't worry, this is not new corruption. These are FREE blocks which will be reused and Oracle will automatically re-format those blocks. Query the v$nonlogged_block view again as given above. We could force re-formatting creating dummy table and inserting data to dummy table. Check Doc ID 336133.1. create table s # n number, c varchar2#4000$ $ nologging tablespace DEMO1; SQL: BEGIN FOR i IN 1..1000000 LOOP INSERT /*+ APPEND */ INTO sys.s select i, lpad#'REFORMAT',3092, 'R'$ from dual; commit ; END LOOP; END; / SQL: drop table sys.s purge; Notice that we don't have corrupted blocks any more. RMAN: backup validate check logical datafile 5;
Views: 130 OracleDBA

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