Performance Tuning :: Does Parallel Hint In Query Can Create Bottleneck / Slowdown / Crash Database
Oct 20, 2011does parallel hint in query can create bottleneck/Slowdown/crash database..??
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Performance Tuning :: Select Query Taking Time Even After Using Parallel Hint?
Sep 25, 2013 select
serialnumber from product where productid in
(select /*+ full parallel(producttask 16) */productid from producttask where
startedtimestamp > to_date('2013-07-04 00:00:00', 'YYYY-MM-DD HH24:MI:SS')
and startedtimestamp < to_date('2013-07-05 00:00:00', 'YYYY-MM-DD HH24:MI:SS')
and producttasktypeid in
[code]....
Explain plan output:
Plan hash value: 2779236890
-----------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name| Rows| Bytes | Cost (%CPU)| Time| Pstart| Pstop |
-----------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT || 1 | 29 | 9633M (8)|999:59:59 |||
|* 1 | FILTER |||| ||||
| 2 | PARTITION RANGE ALL || 738M| 19G| 6321K (1)| 21:04:17 | 1 | 6821 |
[code]....
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter( EXISTS (<not feasible>)
4 - filter("PRODUCTID"=:B1)
5 - filter(ROWNUM<100)
12 - access("MODELID"=:B1)
[code]....
Note: - SQL profile "SYS_SQLPROF_014153616b850002" used for this statement
Performance Tuning :: Does Parallel Hint Works In Cursor Queries
Aug 28, 2013Does parallel hint works in cursor queries? The cursor query is something like :
cursor c is
select /*+ parallel(s,8) */
from table ref_tab s ---- >>
<where condition>;
The table ref_tab hold data for a single day at any point of time and gets truncate before loading the next days data.On average the table holds around 7 million rows and doesn't contains any index (think that's fine as all together we are loading the whole set).And, we are using bulk logic with save exceptions to open the cursor and load the data into the target table.
Performance Tuning :: Can Use Oracle Hint To Use Index In A Query Which Uses UNION
Mar 31, 2011I have a SQL query where I am making UNION of two select statements. The table that I am joining in each select statement have indexes defined for those tables.
Now the UNION of the two select statements again in enclosed in an inline view , from which I fetching my final field values.
The select statements inside the inline view returns huge number of row (like 50 million rows).
The whole query fails with time out.
Is there a way to pass Oracle Hints so that Oracle uses indexes?
Performance Tuning :: Database Crash Due To CPU Starvation?
Sep 1, 2013i am using 11.2.0.3 version of oracle. We have recently migrated to 11g, after 1 month of smooth and comparatively better performance, we are suddenly facing performance issues with our database and it got crashed twice within 5 days. even we didnt push any new code to our database in recent past, atleast after the 11G migration. And after getting feedback from the ORACLE corporation guys , they pointed out about the default database stats gathering job, which was eating most of the CPU, because of the default degree mentioned So it was running in 160 parallel threads causing resource starvation.so we reduce the degree of the stats gathering job to 8 .
But the database crashed again two days back, and rebooted within 3 mins to back to normal, even after this default degree changed to 8. This is happening due to any specific application related sql or anything else.
SQL & PL/SQL :: Query Regarding Parallel Hint Degree?
Jan 3, 2012I have been told that i should use multiple's of 4 as degree in the parallel hint to get maximum performance, so i am wondering is it true? that i should always use multiples of 4 or i can use any number inside the parallel hint.
View 4 Replies View RelatedPerformance Tuning :: Parallel Index With Non-partitioned No-parallel Table?
Apr 30, 2012If we have not set parallel degree for a table then we can ( try to ) force parallel execution on a table using a parallel hint Does this 'parallelism' works on the index search in the query as well?
In which situations non-parallel non-partitioned table but parallel index (degree>2) will facilitate a query?
Performance Tuning :: Hint Is Not Working Properly
Jul 14, 2010I have a query with FULL hint that is behaving in a strange manner. The query fetches around 700000 of data. Sometimes it fetches the data with the hint and sometimes it does not fetch any data with the hint and then I have to remove the hint and have to fetch the data. Below is the query,
select /*+ FULL(COMP_TM) FULL(TRANS_TM) FULL(INVC_TM) */
CUST_BE_ID ,
DISTR_BE_ID ,
FG_BE_ID ,
KIT_BE_ID ,
BG_ID_NO_BE_ID ,
[code]....
The statistics gathering activity of FACT_DLY_ALGND_SLS table takes around 5 hours to complete. It is a range partitioned table with subpartitions.
Performance Tuning :: Syntax To Pass Hint To Emulate Good Attached Plan?
Aug 16, 2012I have an APP that truncates tables and loads data, which in turn makes the stats stale. I ran the query advisor (see attachment) and of course it ecommends running stats or accept a profile.I really don't want to do that as it may cause a load on my DB.
In turn, I would like to consider having my APP team change the query to pass a hint to use the best query plan.syntax to pass the hint to emulate good attached plan? Or is this a bad way to proceed?
select /* INDEX FAST FULL SCAN PK_PLACEMENT_REQUEST_QUEUE */
sum(lastshares) as "ROSEN"
from nyeo.fix_exec_reports fer, nyeo.placement_request_queue q,
nyeo.nyeo_block_control bc
where fer.clordid = q.sequence_number
and q.blockid = bc.blockid
and upper(bc.deskname) like '%ROSEN%'
Performance Tuning :: Querying GTT In Parallel Mode
Apr 24, 2012I am inserting data into a global temporary table and then using 'parallel' hint to query from this temporary table. I remember reading that the queries on the temp table may not run in parallel as the parallel sessions may not be able to see the data in the temporary table
However the execution plan as well as px_session, v$sql indicate that the query on the temporary table in fact run in parallel mode
select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------------------------------
SQL_ID 7d68g52g0mskz, child number 0
-------------------------------------
select /*+ gather_plan_statistics parallel(t,4) */ * from dbo_gtt t order by id,object_id
Plan hash value: 5815349
--------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |Used-Tmp|
--------------------------------------------------------------------------------------------------------------------------
| 1 | PX COORDINATOR | | 1 | | 99999 |00:00:01.46 | 3 | | | |
|
| 2 | PX SEND QC (ORDER) | :TQ10001 | 0 | 1 | 0 |00:00:00.01 | 0 | | | |
|
| 3 | SORT ORDER BY | | 0 | 1 | 0 |00:00:00.01 | 0 | 11M| 1311K| 424K (0)|
|
| 4 | PX RECEIVE | | 0 | 1 | 0 |00:00:00.01 | 0 | | | |
|
| 5 | PX SEND RANGE | :TQ10000 | 0 | 1 | 0 |00:00:00.01 | 0 | | | |
|
| 6 | PX BLOCK ITERATOR | | 0 | 1 | 0 |00:00:00.01 | 0 | | | |
|
|* 7 | TABLE ACCESS FULL| DBO_GTT | 0 | 1 | 0 |00:00:00.01 | 0 | | | |
|
--------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
7 - access(:Z>=:Z AND :Z<=:Z)
select px_servers_executions from v$sql where sql_text like 'select%dbo_gtt t%';
PX_SERVERS_EXECUTIONS
---------------------
0
4
select sid, qcsid, server#, degree from v$px_session where qcsid = 228;
SID QCSID SERVER# DEGREE
---------- ---------- ---------- ----------
247 228 1 4
196 228 2 4
224 228 3 4
234 228 4 4
226 228 1 4
252 228 2 4
212 228 3 4
229 228 4 4
228 228
9 rows selected.
unfortunately I do not have access to get trace (tkprof) report. What must have happened during the execution?
Performance Tuning :: Possible To Build Index Partition In Parallel
Jul 8, 2010Is it possible to build index partition in parallel?I tried following command
alter index <index_name> rebuild partition <partition name> online parallel 5;
It executed without complaining, but want to know if index partitions can be build in parallel?
SQL & PL/SQL :: ORA-30926 Occurs Only With PARALLEL Hint On MERGE Statement
Jun 26, 2013I am writing below MERGE statement. In this cardinality between table_a and table_b is 1:2. I.e. each record in table_b corresponds to 2 records in table_a based on columns in ON clause.
Well this query throws below error.
----Error---
ORA-12801: error signaled in parallel query server P011
ORA-30926: unable to get a stable set of rows in the source tables
However, the same statement executes successfully when PARALLEL hint is removed altogether. (There are no duplicates in table_b based on unit,group,loc columns.)
-----Query--------
MERGE /*+ PARALLEL(8) */
INTO table_a a
USING table_b b
ON (a.unit = b.unit AND a.group = b.group AND a.loc = b.loc)
[Code]....
Performance Tuning :: Parallel Operations Not Executing With Expected Degree
Apr 2, 2012I am executing a sql statement which is doing FTS in parallel mode The server has 8 cpus and threads_per_cpu is 2
The v$sql shows PX_SERVERS_EXECUTIONS as 8
select PX_SERVERS_EXECUTIONS, sql_text from v$sql where sql_id='0q0nk5117yth2'
8, select /*+ full(a) parallel(a)....
however the px_sessions shows 17 sessions (16 parallel session + 1 parent session (where sid = qcsid) Now in px_sessions, these 16 parallel session are divided in 2 server sets 1 and 2 and values for degree and required degree are 8 and 16 respectively
However, all the time, only 8 sessions which belong to server set = 1, were active though its state was waiting with event "PX Deq Credit: send blkd"
The other session which belong to server set = 2 were never active and always had waint event ='PX Deq: Execution Msg'
what could be the reason that 16 parallel session could not be started though I am the only person using the server, there aren't any batch jobs, dbms_jobs,even archivelogs (not a prod system)?
Note that paralel_max_servers setting is 16
Another issue being the duing start of the query approximately 100-115 blocks were read for the query (checked from longops) however after 60-70% blocks are read the number of blocks read / seconds falls down to 10-20 blocks / second across all parallel sessions.
Performance Tuning :: How To Control Concurrent Inserts Of Record By Parallel Sessions
Aug 7, 2012There is a detail table
There is a summary table
During batch process record is entered in detail table as well as summary table.
The process first checks if record exists in summary table for same group_no and if 'yes' then "updates" the record with the newly added amount (sums it) else inserts a new record
Whereas in the detail table it inserts the record directly
detail table :
group_no doc_no amount
101 doc1 100
101 doc2 200
102 doc3 300
102 doc4 400
summary table :
group_no amount
101 300
102 700
Now if the batch process runs in parallel, (out of many) two different sessions insert same group_no; This is because while sesond session inserts a record, first session inserting the same record (group_no) has not yet committed ; So second session Not knowing that already there is same Group_no (101) inserted, again inserts another record with same group_no rather than summing it.
Can it be solved without using temp table, select for update?
Performance Tuning :: Same Query With Different Explain Plan In Two Database?
Aug 17, 2012I am facing a weird situation wherein the explain plan of same sql in SIT and PROD is different.In fact the explain plan is very costly in Prod.Also the DB version of both SIT and PROD is same.
Below is the sql and corresponding explain plan in Prod and SIT respectively.
Query:
SELECT seq,CCN,ProcessorPart,root_item,comp_path,Item,comp_item,comp_item_type,
lag(comp_item_type,1,'PART') over(PARTITION BY seq ORDER BY lvl)Nxt_comp_item_type,lvl,bom_qty,
ROUND(CASE min(abs(bom_qty)) OVER (PARTITION BY seq ORDER BY lvl)
WHEN 0 THEN 0 ELSE 1 END * EXP (SUM (LN (nullif(abs(bom_qty),0))) OVER (PARTITION BY seq ORDER BY lvl))) Ulti_qty,
'AMER'
[code]...
The tables referred in above query is small tables containing arnd 10k records.The above tables are partitioned on Region and not indexed.
Explain Plan in Prod: COST CARDINALITY BYTES
SELECT STATEMENT, GOAL = ALL_ROWS165173613539322883634804
SORT UNIQUE236360
UNION-ALL
PARTITION LIST SINGLE117240
[code]...
Explain Plan in SIT: COST CARDINALITY BYTES
SELECT STATEMENT, GOAL = ALL_ROWS3211689
SORT UNIQUE347240
UNION-ALL
PARTITION LIST SINGLE172120
[code]...
I am not able to attribute why there is a huge change in Cost between SIT and Prod.Apparently the Job is going for 3-5 hours which used to get completed within 20mins in SIT.
Performance Tuning :: Fragmentation Can Reduce Performance In Query Times
Jun 16, 2010I have a question about database fragmentation.I know that fragmentation can reduce performance in query times. The blocks are distributed in many extents and scans process takes a long time. Oracle engine have to locate the address of the next extent..
I want to know if there is any system view in which you can check if your table or index has high fragmentation. If it's needed I will have to re-create, move or rebulid the table or index, but before I want to know if the degree of fragmentation is high.
Any useful script or query to do this, any interesting oracle system view?
Performance Tuning :: Tools For Database Tuning And Instance Tuning
Jul 12, 2010Looking to understand the difference between instance tuning and database tuning.
What is the difference between these two tuning exercises? I understand that an instance is memory based structures (logical) where as database consists of physical structures.
However, how does one tune a database the physical structure? Does it have to do with file placements/block sizes etc. Would you agree that a lot of that is taken care by ASM now in 11g? What tools are required/available (third party as well as oracle supplied) for these types of tuning scenarios?
Performance Tuning :: Query Performance Gain Using Statistics?
Aug 9, 2010Somewhere I read that we should not use hints in Oracle production environments, but we can use hints in the development environment and on achieving the desired execution plan we can adjust the 'statistics' to follow that plan without hints.
Q1. If it is true what statistics do we adjust for influencing the execution plan and how?
For example, I have the following simple query:
select e.empid, e.ename, d.dname
from emp e, dept d
where e.deptno=d.deptno;
emp.empid, emp.deptno and dep.deptno columns have indexes and the tables have the standard structure as found in the basic oracle examples.
If I look at the execution plan of the above query then I see that the driving table is empand the driven table is dept.Also the type of join that is taking place is 'Nested Loop'.
Questions: With respect to the above query,
Q 2. If I want to make dept the driving table and emp the driven table then how can I adjust the statistics to achieve that?
Q 3. If I want to use hash join instead of a nested loop join then then how can I adjust the statistics to achieve that?
I can put the ordered and the use_hash hint to effect this but again I have heard that altering statistics is a more robust way to control an execution plan as compared to hints.
Performance Tuning :: How To Create Index
Mar 30, 2013I am going through this scenario:
* 35 | ID TABLE ACCESS BY INDEX ROW | S_ORG_EXT | 3064K| 2472M| | 1 (0)| 00:00:01 |
| 36 | INDEX FULL SCAN | S_ORG_EXT_U1 | 14 | | | 1 (0)| 00:00:01 |
Predicate Information (identified by operation id):
---------------------------------------------------
35 - filter("T2"."ACCNT_FLG"<>'N' AND ("T2"."INT_ORG_FLG"<>'Y' OR "T2"."PRTNR_FLG"<>'N'))
This unselective index scan on step 36 of the explain is returning 14 rows but optimizer is selecting 3064 K rows from the table .
I tried creating combined index on all 3 columns mentioned in the predicates for 35th step , but that is not utilized .
how to index this whole expression ::--
(ACCNT_FLG<>'N' AND (INT_ORG_FLG<>'Y' OR PRTNR_FLG<>'N'))
Something like CREATE INDEX XYZ on table((ACCNT_FLG<>'N' AND (INT_ORG_FLG<>'Y' OR PRTNR_FLG<>'N')) compute statistics ;
Performance Tuning :: Method Of Tuning Database - Row Reduction?
Oct 20, 2010There is a simple way to increase the performance of a query by reducing the row-size of the table it hits. I used it in the past by dividing the table into smaller parts and querying respective smaller table in each query.
what is this method called ? just forgot the method and can't recall it. what this type of row-reduction optimization is called ?
Performance Tuning :: Procedure Performance On New Database Import?
Nov 15, 2010Testing our 9i to 11g upgrade, we've imported the entire DB into the new machine.We've found that certain procedures are really suffering performance problems. BUT, we've also found, that if we check out a production copy of the procedure from our source code control, and reinstall it, the performance issue goes away. Just alter the procedure and recompiling does NOT work.
The new machine where the 11g database exists is slightly different than the source, but it's not like we have this problem with every procedure. It's only a couple.
any possible reason that we'd have to re-install a procedure to correct a performance problem?
Performance Tuning :: Possible To Create Index Which Would Not Look For N Values
Dec 6, 2011I have column containing three values:-N,E,Y.I want to get results with only E and Y values.Is it it possible to create index which would not look for N values.
View 13 Replies View RelatedPerformance Tuning :: Create Versus Rebuild Index
Jan 27, 2011I was comparing cost of rebuild vs create index...I carried out the following test
SQL> create table t4 as select * from t1;
Table created.
SQL> create table t5 as select * from t1 where 1=2;
Table created.
SQL> create index i5 on t5(id);
Index created. SQL> select bytes,extents,blocks from user_segments where segment_name='I5';
BYTES EXTENTS BLOCKS
---------- ---------- ----------
65536 1 8
SQL> alter index i5 unusable;
Index altered.
SQL> alter table t5 nologging;
Table altered.
SQL> Alter session set skip_unusable_indexes=True;
Session altered.
SQL> insert /*+ append */ into t5 select * from t1;
563904 rows created.
SQL> commit;
Commit complete.
Now I compared the cost (elapsed time, logical I/O) of the operations
create index i4 on t4(id);
Vs
alter index i5 rebuild online;
Following is the related trace of above 2 steps
create index i4 on t4(id)
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 1 0 0
Execute 1 1.17 3.38 9497 7869 335 0
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 2 1.17 3.38 9497 7870 335 0
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 5
[code]....
So which option we shall pick in such cases? {Of course I haven't set 'nologging' for the indices but it is same for both indices we are comparing}
Performance Tuning :: Create Table Statement With Union?
Aug 5, 2010this statement is taking 1hr , can we reduce the timing?
CREATE TABLE DGT_ITEMEFFORTDATA (ENTERPRISEID, OWNERTYPE, OWNERID, SUPEROWNERTYPE, SUPEROWNERID,
ITEMTYPE, ITEMID, STAGEID, USERID, DATEIDENTIFIED,
DATECLOSED, ACTIVITYCODEID, PHASEID, RELEASEID, MONTHID,
QUARTERID, INITIALEFFORT, BASELINEDEFFORT,
ACTUALEFFORT, ITEMSTATUS, ALLOCATIONSTATUS, STAGESTATUS,
OCCURANCETYPE, DSLPROJECTTYPE, METRICCALCRUNID,
[code].....
This is the explain plan of the above query
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%C
--------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 11M| 4137M| 46149 (
| 1 | UNION-ALL | | | |
| 2 | TABLE ACCESS FULL| DGT_ITEMEFFORTDATA_DAILY | 3455K| 428M| 14575
[code].....
This is the index details
1DGT_ITEMEFFORTDATA_DAILYHCLT_IDX_DGT_IFDITEMID4
2DGT_ITEMEFFORTDATA_DAILYHCLT_IDX_DGT_IFDITEMTYPE3
3DGT_ITEMEFFORTDATA_DAILYHCLT_IDX_DGT_IFDOWNERID2
4DGT_ITEMEFFORTDATA_DAILYHCLT_IDX_DGT_IFDOWNERTYPE1
There is no index on DGT_ITEMEFFORTDATA_TEMP table
[code].....
Performance Tuning :: Create Hash Partition On Fact Tables?
Aug 5, 2010I have to create a hash partition on fact tables.. we can use temp tablespace or permanent tablespace.
View 10 Replies View RelatedPerformance Tuning :: Same Execution Plan For Create Table Statement When Name Changes?
May 18, 2010Can we have same execution plan for a create table statement where the name of the table changes every time as follows:
create table test
as
select * from t1
Here table name changes from test to another table name next time
Performance Tuning :: Create Statements On A Highly Fragmented Disk
Nov 24, 2010On Oracle 10g, I create, delete and drop a lot of tables. Therefore, the disk is highly fragmented.The execution of a very simple create statement takes more than a minute. If I execute the same statement but first truncate the table and insert the data, it takes less than a second!
I think this has to do with the high fragmentation of the disk. Obviously, I can defragment the disk, but I will always have a high fragmentation since I use a lot of create, delete and drops.
how I can improve the performance of create statements on highly fragmented disks?
Performance Tuning :: How To Show Right IO Of Query
Jun 21, 2011I use oracle 11g r2
i have created a table for objects
create table table_t
(Record_no number,
t_no number,
position SDO_GEOMETRY
, occupation_time number);
and inserted many values (examples below )
INSERT INTO tra VALUES
(2,
20503,
SDO_GEOMETRY
(2001,
NULL,
SDO_POINT_TYPE (1387, 0, NULL),
NULL,
NULL),
23037
)
/
and( position) indexed as Rtree spatial index
now when i run spatial query such as
SELECT * FROM tra t WHERE
SDO_FILTER(t.position, MDSYS.SDO_GEOMETRY(2001,NULL,NULL, MDSYS.SDO_ELEM_INFO_ARRAY(1,1003,3),
MDSYS.SDO_ORDINATE_ARRAY(0,0,9000,0)), 'querytype=WINDOW') = 'TRUE' and t.position.sdo_point.X=1;
i do not know how many IO accrued ?
i tried set autotrace on
but the physical read is 0 , this is not possible because i have more than 100000 objects there and all indexed as R-tree
Performance Tuning :: Query Doing FTS On A Big Table
Jun 24, 2011Below query is taking a long time...
select gam.SOL_ID,COUNT(gam.FORACID) from gam,smt where
gam.ACID=smt.ACID and gam.ACID NOT IN(select ACID from imt) and
gam.SCHM_TYPE in('SBA','CCA','CAA','ODA') and GAM.ACCT_CLS_FLG='N' and
gam.SOL_ID IN(select SOL_ID from IMT) group by gam.SOL_ID
/
attached is the explain plan.
in which index on IMT table is not used. And the query is doing a FTS on IMT table. What needs to be done to avoid FTS on IMT table.
Performance Tuning :: When To Use Sub-query And When To Use Join
Dec 14, 2010In SQL, almost all the thing which are possible with join is possible with sub-query also and vice-a-versa.
So when should I use sub-query and when should I go for join?