Performance Tuning :: Cost Calculation For Nested Loop Join
Mar 27, 2012
Following is the query on TPC-H schema.
explain plan for select
count(*)
from
orders,
lineitem
where
o_orderkey= l_orderkey.
The trace 10053 (as shown below) for this query shows nested loop join with Lineitem as outer table and Orders as inner table. It is effectively join on composite index (pk_lineitem) of Lineitem and unique index(Pk_orderkey) of Orders table. The cost calculation formula as given in the book as "outer table cost + cardinality of outer table * inner table cost " fails here. I am not able to understand this.
BASE STATISTICAL INFORMATION
***********************
Table Stats::
Table: LINEITEM Alias: LINEITEM
#Rows: 6001215 #Blks: 109048 AvgRowLen: 124.00
Column (#1): L_ORDERKEY(NUMBER)
AvgLen: 6.00 NDV: 1500000 Nulls: 0 Density: 6.6667e-07 Min: 1 Max: 6000000
[code]....
how the cost has been calculated. This does not follow the traditional nested loop cost formula as mentioned in the book.
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Oct 18, 2012
I want to know how the Oracle optimizer choose joins and apply them while executing the query. So that I will insure about optimizer join before writing any query.
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Jun 23, 2011
I'm joinging two tables event_types and tmp_acc tables.
event_types contains 2 Billion records
tmp_acc contains 20,000 records.
Resulting rows are about 300,000 records in event_types table end_t and account_obj_id0 are joined indexed
no indexs in tmp_acc.
When I run below query with nexted loop it takes 6 hrs to complete. But when I run with hash join even after 4 days it was still running. what is wrong with hash join here. Why it takes so long. I'm joining only 20000 rows. So I think there should be a way to get result rows quickly.
show parameters hash_area_size
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
hash_area_size integer 2097152
explain plan for
select --+ parallel(e,6)
[code]....
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Oct 30, 2012
I want to make sure I am describing correctly what happens in a query where there is distributed database access and it is participating in a NESTED LOOPS JOIN. Below is an example query, the query plan output, and the remote SQL information for such a case. Of particular note are line#4 (NESTED LOOPS) and line#11 (REMOTE TABLE_0002).
What I want to know is more detail on how this NESTED LOOPS JOIN handles the remote operation. For example, for each row that comes out of line#5 and is thus going into the NESTED LOOPS JOIN operation @line#4, does the database jump across the network to do the remote loopkup? Thus if there are 1 million rows, does that mean 1 million network hops? Does batchsize play a role? For example, if the database batches in groups of 100 then does that mean 10 thousand network hops?
I think each row that comes out of line#5 means a network hop to the remote database. But I do not know for a fact.I have done some abbreviating in the plan in an attempt to make it fit on the page (line#7 TA = TABLE ACCESS).
SELECT A.POLICY ,
F.MIN_MEMBER_ID,
MIN(A.EFF_DATE) EFF_DATE,
A.EXP_DATE ,
G.DESCRIPTION PROGRAM_NAME,
[code]...
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Jul 23, 2010
I am facing one performance issue, in which the query cost is very low compare to cpu cost and as a result the cpu always show the high graph.I am also attaching the gv$sql and gv$sql_plan data of this query.
This is the query:
SELECT PTLS.ITEMTYPE , PTLS.ITEMID , PTLS.STAGEID, TS.USERID, SUM(PREVIOUSHOURS) AS PREVIOUSHOURS, MIN(STARTDATE) AS STARTDATE, MAX(STARTDATE) AS ENDDATE FROM PROJECTTIMELOGSSTAGE PTLS, PROJECTTIMESHEETITEM PTSI, TIMESHEET TS WHERE PTLS.PROJECTID = :B2 AND TS.TIMESHEETID = PTSI.TIMESHEETID AND TS.USERID = :B1 AND PTSI.TIMESHEETID = PTLS.TIMESHEETID AND PTSI.ITEMTYPE = PTLS.ITEMTYPE AND PTSI.ITEMID = PTLS.ITEMID AND (PTSI.ISPWFITEM = 'N' OR PTSI.ISPWFITEM IS NULL) AND PTLS.ITEMTYPE NOT IN ('OtherTsk','NewTsk','Loc','Glb') AND (PTLS.ITEMTYPE, PTLS.ITEMID ) IN (SELECT ITEMTYPE, ITEMID FROM PROJECTTIMELOGSSTAGE PTLS1 WHERE PTLS1.PROJECTID = :B2 AND PTLS1.TIMESHEETID = :B3 ) GROUP BY PTLS.ITEMTYPE, PTLS.ITEMID, PTLS.STAGEID, TS.USERID
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Aug 4, 2010
I am working on Tuning a Materialized view. I was getting an error saying ORA-12008: error in materialized view refresh path
ORA-12801: error signaled in parallel query server P002, instance hrms-stg-db01:HRSTG1 (1)
ORA-01652: unable to extend temp segment by 16 in tablespace TEMP1.
so i increased the temp size. I am trying out various hints to get it rectified. But i am not sure if i should go for less cost or less bytes.
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Jan 22, 2009
how to reduce the cpu cost for a query at query level.
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Mar 21, 2013
I have Following wjich takes some minutes to executes i want to be tune so this query Executes fast.
Query :
SELECT a.CHDR_EXCH_CD ,TMHR_EXCH_TM_CD,'S' Sec_type,
round(SUM (Decode(csdt_Depo_Typ,'I',(Cal_Scheme_Rate(csdt_rsm_code,TO_DATE(:P_DT_FR,'DD-MM-RR'),csdt_stsc_cd,csdt_scp_qty)*csdt_scp_qty)-
(Cal_Scheme_Rate(csdt_rsm_code,TO_DATE(:P_DT_FR,'DD-MM-
[Code]...
Explain Plan Result :
Plan
SELECT STATEMENT ALL_ROWS
Cost: 1,669 Bytes: 67 Cardinality: 1
15 HASH GROUP BY
Bytes: 67 Cardinality: 1
14 CONCATENATION
[Code].....
After i see result , no 4 in explain plan result gives TABLE ACCESS FULL . i want to be indexing on that how to do this..
This table MG_COLL_SCP_DTL have index like this
CREATE UNIQUE INDEX CSDT_PK ON MG_COLL_SCP_DTL
(CSDT_CHDR_TRANS_NUM, CSDT_PROD_TYP, CSDT_TRAN_SR_NO, CSDT_CHDR_CDTL_COLL_TYP, CSDT_CHDR_CDTL_COLL_TYP_CD,
CSDT_STSC_CD, CSDT_CHDR_CLNT_CD, CSDT_CHDR_CLNT_TM_CD)
[Code]....
How to Reduce cost ???
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Sep 1, 2010
For an query, cost was 16Lakhs and was taking 30min, I brought down the cost to 1.5lakhs, but still it is taking 30min.
There were many outer joins and same table has been Used(FROM clause) 5 times in the query. I have introduced WITH clause, and brought down the cost.
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Dec 12, 2011
Till statspack we had
elapsed time = time spent on waits + time CPU was used
Total time during snaps = Elapsed time + (may be) time waited for CPU...In AWR is it possible to draw such equation? I can see that the AWR report has following elements
1) End Snap time - Begin Snap time
2) DB time - as mentioned at the top of AWR report
3) DB CPU - in "Top 5 Timed Foreground Events" (I assume this is 'CPU used by sesson timing' in statspack)
4) Total of time for all Statistics in "Time Model Statistics"
5) BUSY_TIME + IDLE_TIME - "Operating System Statistics"
Time between 2 snapshots? or what else? Also for which seconds to multiply to 'DB Time(s)' per second and 'DB CPU(s)' per second in Load Profile to get the db time and CPU time?
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Sep 14, 2010
10.2.0.1
I am trying to understand the concept of nested loops.
--------
| 0 | SELECT STATEMENT | | 14 | 364 | 4 (0)| 00
:00:01 |
| 1 | NESTED LOOPS | | 14 | 364 | 4 (0)| 00
:00:01 |
[Code]....
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("A"."DEPTNO"="B"."DEPTNO")
Nested loop by defintion means,for every row returned by the outer query,the inner query is executed that many times.
In the above example,oracle does a full table scan and returned 14 rows.Now for dept table,it does a index unique scan and applies the predicate a.deptno=b.deptno and returns 1 row.
My question is why it is returning only 1 row? That measn for every 14 rows,this one row is fetched 14 times.
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Mar 11, 2011
Can this be optimized, in dev and Ist we didn't realize since 1000 rows were there, but in PERF since 2 mil rows are there this is taking a long time,
SET SERVEROUTPUT ON
DECLARE
counter number := 0;
CURSOR insertValues IS select roleid, productcode, functioncode, typecode, restrictiontype, value1 from restrictions where actionmode = 'INSERT';
[code]...
can this be done in a single update since Selects /Updates are happening on same table
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Sep 18, 2012
So usually joining a local table and a remote table (much larger table), the best practice is using a /*+ DRIVING_SITE(remote table) */ hint.
*CASE1:
INSERT INTO another_local_table
SELECT /*+ DRIVING_SITE(remote_table) */
FROM local_table
,remote_table@remotedb
WHERE join condition
*CASE2:
However I saw this particular
FOR x IN Select id From local_table l
LOOP
INSERT INTO another_local_table
[code]...
So far I haven't seen the explain plan of both cases since most of the tables are Global temporary tables. But in terms of the logic of the two cases and the common best practice, logically doesn't CASE1 should have a better performance?
For me, its like taking a trip to a grocery. CASE1 buys all that you need, one time, it will take you a half-day trip perhaps. However CASE2 is like quickly buying a grocery item, one at a time, for several short trips. You'll save on gas on CASE1 right.
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Sep 8, 2009
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi
PL/SQL Release 10.2.0.4.0 - Production
CORE 10.2.0.4.0 Production
TNS for Solaris: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
5 rows selected.
I have a problem with views and nested selects which I cannot explain. Here is a trimed down version of the research I have done. notice the following:
1) all code is executed from the same user CDRNORMALCODE. this user has all views and procedural code
2) all data is owned by a different user CDRDATA. This user has no views and no code.
My problem is this:
If I reference the table directly with a delete statement that uses a nested select (i.e. IN clause with select), the index I expect and want is used.But if I execute the same delete but reference even the most simple of views (select * from <table>) instead of the table itself, then a full table scan is done of the table.
Here is an execute against the table directly (owned by cdrdata). Notice the reference to the table in the table schema on line 3. Also please notice INDEX RANGE SCAN BSNSS_CLSS_CASE_RULE_FK1 at the bottom of the plan.
SQL> show user
USER is "CDRNORMALCODE"
SQL>
SQL> explain plan for
2 delete
[code]...
OK, here is an update. The views I am useing normally have instead of triggers on them. If I remove the instead of trigger the problem looks like it goes away, when I put the trigger back the problem comes back.But why would an instead-of-trigger change the query plan for a view?
SQL> DELETE FROM PLAN_TABLE;
5 rows deleted.
SQL> explain plan for
2 delete
3 from BSNSS_CLSS_MNR_CASE_RULE_SV
[code]...
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Jan 16, 2012
I have to do the optimization of a query that has the following characteristics:
- Takes 3 hours to process
- Performs the inner join with 30 tables
- Produces an output of 280 million records with 450 fields
First of all it is not feasible to make 30 updates (one for each table) to 280 million records.
The best solution that I had found so far was to create 3 temporary tables, where each of them to do the join with 1/3 of the 30 tables, and in the end I make the join between the main table and these three tables temporary.
I know that you will ask (or maybe not) to the query and samples, but it is impossible to create 30 examples.
how to optimize this type of querys that perform the join with multiple tables and produce a large output with (too) many columns.
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Dec 14, 2010
In 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?
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Mar 14, 2012
For a hash join statement, is it beneficial to have the join condition objects in the index as well as the objects in the where clause?
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Oct 14, 2013
I'm looking to see if there is a way (fully expecting it to be an underscore, or two...) to force the optimizer to keep churning until all permutations are exhausted.I'm aware that it, to paraphrase, cuts out when it's spent more time parsing than it would just running it based on it's estimates.
I've got some irritating problems with xml rewrite, xml indexes and access paths/cardinalities etc and I'm really needing the entire thing considered as a one off for debugging this. I've already cranked up the maximum permutations to the max but it's not enough, it shorts out after 5041 permutations (I'd set that to 80000 max).
I know you'd not want to do this in the real world but I cant get the damned thing to run the plan I want in a 10053 so I can see the values it has there. I know I can hint it, but I'm trying to ascertain why it's not even considering it in a "normal" parse.
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Nov 14, 2012
The product I work on requires a query to tell us what tables are dependent on certain types.
SELECT dba_tab_cols.owner,
dba_tab_cols.table_name,
dba_tab_cols.data_type_owner,
dba_tab_cols.data_type
FROM dba_tab_cols
JOIN dba_types
ON dba_types.owner = dba_tab_cols.data_type_owner
AND dba_types.type_name = dba_tab_cols.data_type
WHERE (dba_types.owner IN ('SCHEMA1', 'SCHEMA2'......))
I find this query to be pretty slow. I think it is because data_type_owner in dba_tab_cols is not indexed. Adding an index is not an option because users expect our product to read-only.
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Oct 24, 2011
however I was able to identify a poorly performing query that seemed to be maxing out our CPU. I have been trying to understand the Explain Plan. The plan below is from our test system which has considerably less information in the tables than our PROD system.
I can see there are a bunch of table scans at the end which may indicate missing indexes, but I am unclear on whether this is actually a problem as the %CPU seems to be worse for the JOIN near the top of the plan.
-------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | Inst |IN-OUT|
-------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1870M| 3018G| | 677M (1)|999:59:59 | | |
| 1 | SORT ORDER BY | | 1870M| 3018G| 3567G| 677M (1)|999:59:59 | | |
[code]...
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Sep 12, 2011
Having production system: 11.2.0.1 on Windows Server x64
Test system: 9.2.0.1 on Windows XP
Problem preface: to get all unique CASEID which should be checked up by biometric system.What i should check - all CASEs for different PERSONs having same PHONEs at least among one phone type (1..4).Real table contains little bit more than 10 million records.I made test scripts.
Below the DDL for test table creation:
------------------------------------------
-- Create CASEINFO test table
------------------------------------------
DROP TABLE CASEINFO;
CREATE TABLE CASEINFO
[code]...
Below i've put SQL/DLL to make test data.number of records inserted 2 millions.
PERSON_COUNT := #/8;
------------------------------------------
-- fill CASEINFO with sample data
------------------------------------------
DECLARE
I INTEGER;
[code]...
Below SQL select to check the data in created table.
------------------------------------------
-- Check test data counters
------------------------------------------
SELECT 'TOTAL',count(*) from CASEINFO
UNION ALL
SELECT 'LEGAL',count(*) from CASEINFO where
[code]...
The PROBLEM is that i am experiencing HUGE perfomance problems on both test and production systems with that query:
select distinct b.caseid
from CASEINFO a, CASEINFO b
where (a.person<>b.person) and (a.sex=b.sex) and
(
(a.phone1=b.phone1) or
(a.phone1=b.phone2) or
(a.phone1=b.phone3) or
[code]...
This query takes almost 90 minutes to execute.And i do not know how to avoid this.Full SQL file to make test attached.
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Oct 18, 2010
I am posting the below query:
SELECT PEA.INCURRED_BY_PERSON_ID AS PERSON_ID,
PEA.EXPENDITURE_ENDING_DATE AS WEEK_END_DATE,
CASE
[Code].....
The explain is below:
SELECT STATEMENT ALL_ROWSCost: 48,287 Bytes: 18,428,818 Cardinality: 297,239
3 HASH JOIN Cost: 48,287 Bytes: 18,428,818 Cardinality: 297,239
1 TABLE ACCESS FULL TABLE PA.PA_EXPENDITURES_ALL Cost: 2,964 Bytes: 3,506,094 Cardinality: 194,783
2 TABLE ACCESS FULL TABLE PA.PA_EXPENDITURE_ITEMS_ALL Cost: 43,425 Bytes: 26,637,468 Cardinality: 605,397
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Jul 7, 2012
Where filter middle_rows save before join and grop by operation?
It is save rows in PGA Private SQL Area or save blocks in SGA databuffer?
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Sep 5, 2013
collection1
============
SELECT o.object_id
BULK COLLECT INTO l_obj_info
FROM (SELECT n.node_id, n.object_id
FROM nodes n
START WITH n.node_id = 100
CONNECT BY PRIOR n.node_id = n.parent_node_id) n
INNER JOIN objects o ON n.object_id = o.object_id
WHERE o.object_type_id = 285;
collection2
============
SELECT *
BULK COLLECT INTO l_tab
FROM ((SELECT REGEXP_SUBSTR (i_l_text, '[^,]+', 1, LEVEL)
FROM DUAL
CONNECT BY REGEXP_SUBSTR (i_l_text, '[^,]+', 1, LEVEL) IS NOT NULL));
END;
collection3
============
SELECT o.object_id
BULK COLLECT INTO l_fin_tab
FROM objects o JOIN ATTRIBUTES att ON o.object_id = att.object_id
WHERE o.object_id = collection1.object_id
AND att.VALUE = collection2.val;
how to implement for loop in the collection3 to get the values from collection1 and collection2. i have tried in the below way
CREATE OR REPLACE TYPE LIST_OF_ATTRIBUTES_TYPE AS TABLE OF varchar2(4000);/
CREATE OR REPLACE TYPE LIST_OF_OBJECT_IDS_TYPE AS TABLE OF number(9);/
CREATE OR REPLACE FUNCTION f_get_objects_by_type_id ( i_object_type_id IN NUMBER, i_l_text IN VARCHAR2, i_scope_node_id NUMBER)
[Code]....
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Jul 29, 2013
I am using a record type to print some column in a same line.
Eg: I want to create index on some composite key columns. But i dont know how many columns are there. So want to use a loop which will count the number of column and then create the index like:
CREATE INDEX PRODUCT.XIF1AGMNT_PROD ON PRODUCT.AGMNT_PROD(LOAN_ID,LOAN_PROD_STRT_DT) TABLESPACE PRODUCT_INDEX;
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Jul 21, 2011
I loop through the 1st cursor (account_csr), while in the 1st csr loop, based on some conditions being true, I want to loop through a 2nd cursor (acctper_csr) but I only want to retrieve data/rows in the 2nd cursor where the account_id column in 1st cursor = account_id column in the 2nd cursor. This will enable me to pull all the account_periods for each account I loop through in the first cursor.
I have attempted several different ways and cannot make this work. Thought I could somehow define a variable and store the account_id from 1st cursor and use on the 'where' clause in the 2nd cursor definition. Have not been able to make this work successfully.
Following is the sample of my
--First cursor (accounts)
CURSOR account_csr is
SELECT *
FROM s_dev_xref1.account A
WHERE a.source = 1
[Code]...
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Oct 8, 2013
How to create this pl/sql process to add elements to a nested table or varray within a loop. Here's the scenario: I have an apex package that has some pl/sql processes and some stored procedures. I am dealing with Inspection Areas. An Inspection Area has several sectors. I already have the loop that lists all the Inspection Areas and a loop inside that loop that lists all the sectors. There is an if statement that determines whether or not the sector name gets stored in the varray or table. I am not sure how to correctly do this and am not sure whether to use a nested table or varray. I've posted somewhat of a pseudo coded example below
If (you_belong_in_table) then
variable := store_me_in_varray /* OR */
variable := array_type(sector.sector_name)
i := i + 1;
end if;
/* Now we output our varray or table */
start loop
output(sector names one by one)
end loop I hope this makes sense. I more so just need the syntax to be able to continually added values to a table or varray while I'm already inside a loop; and also how to output those values end the end as well.
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Mar 16, 2011
What is the difference between Hash join and Nested Loops in pl / sql?
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Mar 22, 2012
these are the sample data :
CREATE OR REPLACE TYPE CourseList AS TABLE OF VARCHAR2(64);
CREATE TABLE department (
courses CourseList)
NESTED TABLE courses STORE AS courses_tab;
INSERT INTO department (courses)VALUES (CourseList('1','2','3'));
[code]....
The query returns the correct data, CourseList that are not subset of any other CourseList of the table.
I am trying to convert this not exists in a left outer join query to check if the performance is better, but I don't know how to do it.
I was making some variations of this code :
select d1.courses c_1, d2.courses c_2
from department d1,department d2
where d1.courses<>d2.courses(+);
but it is now working.
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Feb 18, 2011
I have created table with nested table:
CODECREATE OR REPLACE TYPE ADDR_T AS OBJECT (
ADDR1 VARCHAR2 (50),
ADDR2 VARCHAR2 (50)
);
CREATE OR REPLACE TYPE t_ADDr AS TABLE OF ADDR_T;
[code]....
I have added some records and created index on ID column. I want to get result of CODEselect id, p.addr1,p.addr2 from nested_table n,table(n.COL1) p where id=1
Explain plan for that is:
CODESELECT STATEMENT ALL_ROWSCost: 8 Bytes: 231 Cardinality: 3
4 HASH JOIN Cost: 8 Bytes: 231 Cardinality: 3
2 TABLE ACCESS BY INDEX ROWID TABLE SYS.NESTED_TABLE Cost: 2 Bytes: 13 Cardinality: 1
1 INDEX RANGE SCAN INDEX SYS.FDSFAS Cost: 1 Cardinality: 1
3 TABLE ACCESS FULL TABLE (NESTED) SYS.COL1_TAB Cost: 5 Bytes: 163,840 Cardinality: 2,560
How to avoid full table scan on nested table? Cardinality is sum of all records in nested column in all rows in main table, why?
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