Is Index Required?
Hi All,
I have a table B with Column ID (Primary Key ) with Reference on table A with Column ID (PK).
Is it required to create Index for this foreign key of Table B?
Thanks,
Jacob
user545846 wrote:
Hi All,
I have a table B with Column ID (Primary Key ) with Reference on table A with Column ID (PK).
Is it required to create Index for this foreign key of Table B?
Thanks,
JacobIt is a good concept to always index a foreign key column.
One reason is that if you delete a record from the parent table then oracle issues a "select null from childtable where fk_column = Parentkey;" this select is needed to prevent the delete when child records exists. Without an index this select will be doing a full table scan on the child table and the delete will be very slow.
If the FK column in the child table is also the PK in the child table (strange concept but possible) then you have the index provided by the PK constraint automatically. You can't add a second index to this column then.
Edited by: Sven W. on Aug 7, 2009 1:50 PM
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Syntax for CONTEXT Indextype
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Hi,
There is a Secondary index created on a Z table which already have 9 secondary indexes. This is the 10th index that is created.
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MANDT Client
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What else I need to check , so that the index improves the performance. The table is using in 300 reports.Ravishankar Lanjewar wrote:
@SAP LEARNER,
>
> There is a Secondary index created on a Z table which already have 9 secondary
> indexes. This is the 10th index that is created.
>
>
> I will not recommand to create index any more on this table. If you want to create secondary index for on above table which you have mention. You don't create index only for hamper of performance of single program/report.
>
> Don't create more than 4 to 5 index on sinlge table.
>
> Refere the tread Link:[Why to create Secondary index ?|Re: When is a secondary index used (in select or where)]
Sounds like another myth that is widely spread across SAP community.
Remember, complex systems like modern DBMS do not like generalizations. I personally know standard SAP tables with 9 standard secondary indexes. In the meantime the hardware became fast enough to update several secondary indexes without really significant problems. Of course indexes require space, of course one should create indexes that are not similar and differ from each other with more than one field for example. In other words, think before creating!
But it's again incorrect to say "do not create because you already have 9 others". You did not even ask what fields are in the affected table, what are the existing indexes.
Ravishankar Lanjewar wrote:
> I will recommand to delete all the index and create 4 to 5 fresh index while doing analysis for all SQL statement using where use list depends on where condition of SQL.
I am now trying to imagine the effort to analyze 300 reports using this table and all corresponding selects. And probably you will drop supporting indexes for several reports. Some of them may be CEO/CFO-relevant reports that will run minutes/hours instead of seconds. And I would like to see the reaction of CEO when he finds out that it was the result of your "optimization" activities. -
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Sue -
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Hi all
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I have a table with more than a 100 million records in production.
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I have done some statistical analysis in the development environment though according to which dropping and recreating indexes is feasible if the number of records inserted at once is less than 500.
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Edited by: 834445 on Feb 13, 2011 1:45 AM834445 wrote:
I have a table with more than a 100 million records in production.
There are a total of 6 indexes on the table out of which 4 are bitmap indexes.
At the end of the year the table is populated with data. I am not aware of how many records are inserted into the table at once.
I have done some statistical analysis in the development environment though according to which dropping and recreating indexes is feasible if the number of records inserted at once is less than 500.
But the table count in development is only 7 million, far less than the production.
Please advise what is the best possible way. Is there a need to drop and recreate indexes and if yes are all indexes required to drop or only the bitmap ones.
Note: I am using oracle 10g database
Always a difficult call to make, but doing some experiments as you are doing is a good start.
Other points to consider - how much down-time are you given for this load, or are people expecting to access the table while it's going on - does the table get more rows added bit by bit over the course of the year - is there a big delete that happens before or at about the same time as the big insert.
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Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk
A general reminder about "Forum Etiquette / Reward Points": http://forums.oracle.com/forums/ann.jspa?annID=718
If you never mark your questions as answered people will eventually decide that it's not worth trying to answer you because they will never know whether or not their answer has been of any use, or whether you even bothered to read it.
It is also important to mark answers that you thought helpful - again it lets other people know that you appreciate their help, but it also acts as a pointer for other people when they are researching the same question, moreover it means that when you mark a bad or wrong answer as helpful someone may be prompted to tell you (and the rest of the forum) what's so bad or wrong about the answer you found helpful. -
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I am using 10g.
3.What will be the best option to reclaim space used by unused indexes,compressing or dropping those.
please let me know your suggestions.user610910 wrote:
I am using the below query to check index usage statistics.
I queried some tables and checked that these were accessing some indexes in explain plan.
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Can anyone suggest me a better alternative.The query is based on your AWR repository. Unfortunately the AWR by default captures only the Top N SQLs, so using this approach is likely to miss a lot of indexes and therefore is unreliable (and it's not reasonable either to re-configure your AWR to capture all SQLs).
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Regards,
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http://oracle-randolf.blogspot.com/
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Regards,
Vadamalai A -
Hi ,
What is difference between normal index and domain index?
Please help.
Thanks.>
What is difference between normal index and domain index?
>
Domain indexes are custom indexes that you provide the code to manage: create, update, delete values.
Normal indexes are the indexes that Oracle makes available out-of-the-box as standard functionality.
If you need to index non-relational data or have unique indexing requirements (e.g. to index binary data) Oracle provides Data Cartridge functionality that allows you to extend Oracle to include your own indexing code.
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See Overview of Indextypes and Domain Indexes
>
Overview of Indextypes and Domain Indexes
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3.Check the Registry Value
Manual Fix 1
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2. Type "regedit.exe" in the box and hit enter.
3. Using the box on the left, navigate to the following directory:
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7. Restart your computer.
Manual Fix 2
Using the above information navigate to the following directory: Read More on http://bookingtohosting.blogspot.com/2015/04/windows-8-hangs-or-freezes-whenever.htmlHi,
Regarding current information we can't say that it related to this exe file.
We need to use Clean boot mode and Safe mode to test the results:
Please first restart the Windows in Clean boot and see if the issue still persists after reboot:
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http://support.microsoft.com/kb/929135
If the issue doesn’t appear, you can determine which one can be the cause by using dichotomy in MSconfig. Checking on half of Non-Microsoft service and restart, determining which half of the services cause the issue and repeating to check half of the problematic
half services.
If the issue still persists in Clean boot mode, please test in Safe mode.
Let me know the results in Safe mode.
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Windows Performance Toolkit: Simple Boot Logging
http://www.autoitconsulting.com/site/performance/windows-performance-toolkit-simple-boot-logging/
You can upload the etl file from this tool for our research.
Kate Li
TechNet Community Support -
Why is LOWER function producing a cartesian merge join, when UPPER doesn't?
Hi there,
I have an odd scenario that I would like to understand correctly...
We have a query that is taking a long time to run on one of our databases, further investigation of the explain plan showed that the query was in fact producing a Cartesian merge join even though there is clearly join criteria specified. I know that the optimiser can and will do this if it is a more efficient way of producing the results, however in this scenario it is producing the Cartesian merge on two unrelated tables and seemingly ignoring the Join condition...
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SELECT count(*)
FROM srs_sce sce,
srs_scj scj,
men_mre mre,
srs_mst mst,
cam_smo cam,
ins_spr spr,
men_mua mua,
temp_webct_users u
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AND sce.sce_stuc = mre.mre_code
AND mst.mst_code = mre.mre_mstc
AND mre.mre_mrcc = 'STU'
AND mst.mst_code = mua.mua_mstc
AND cam.ayr_code = sce.sce_ayrc
AND cam.spr_code = scj.scj_sprc
AND spr.spr_code = scj.scj_sprc
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AND SUBSTR (sce.sce_ayrc, 1, 4) = '2008'
AND sce.sce_stac IN ('RCE', 'RLL', 'RPD', 'RIN', 'RSAS', 'RHL_R', 'RCO', 'RCI', 'RCA');
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SELECT STATEMENT CHOOSECost: 83
20 NESTED LOOPS Cost: 83 Bytes: 176 Cardinality: 1
18 NESTED LOOPS Cost: 82 Bytes: 148 Cardinality: 1
15 NESTED LOOPS Cost: 80 Bytes: 134 Cardinality: 1
13 NESTED LOOPS Cost: 79 Bytes: 123 Cardinality: 1
10 NESTED LOOPS Cost: 78 Bytes: 98 Cardinality: 1
7 NESTED LOOPS Cost: 77 Bytes: 74 Cardinality: 1
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3 BUFFER SORT Cost: 71 Bytes: 1,340,508 Cardinality: 51,558
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SELECT count(*)
FROM srs_sce sce,
srs_scj scj,
men_mre mre,
srs_mst mst,
cam_smo cam,
ins_spr spr,
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AND mst.mst_code = mua.mua_mstc
AND cam.ayr_code = sce.sce_ayrc
AND cam.spr_code = scj.scj_sprc
AND spr.spr_code = scj.scj_sprc
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SELECT STATEMENT CHOOSECost: 13
20 SORT AGGREGATE Bytes: 146 Cardinality: 1
19 NESTED LOOPS Cost: 13 Bytes: 146 Cardinality: 1
17 NESTED LOOPS Cost: 12 Bytes: 134 Cardinality: 1
15 NESTED LOOPS Cost: 11 Bytes: 115 Cardinality: 1
12 NESTED LOOPS Cost: 10 Bytes: 91 Cardinality: 1
9 NESTED LOOPS Cost: 7 Bytes: 57 Cardinality: 1
6 NESTED LOOPS Cost: 6 Bytes: 31 Cardinality: 1
4 NESTED LOOPS Cost: 5 Bytes: 20 Cardinality: 1
1 TABLE ACCESS FULL EXETER.TEMP_WEBCT_USERS Cost: 3 Bytes: 6 Cardinality: 1
3 TABLE ACCESS BY INDEX ROWID SIPR.MEN_MUA Cost: 2 Bytes: 42 Cardinality: 3
2 INDEX RANGE SCAN EXETER.TEST Cost: 1 Cardinality: 1
5 INDEX UNIQUE SCAN SIPR.SRS_MSTP1 Cost: 1 Bytes: 11 Cardinality: 1
8 TABLE ACCESS BY INDEX ROWID SIPR.MEN_MRE Cost: 2 Bytes: 26 Cardinality: 1
7 INDEX RANGE SCAN SIPR.MEN_MREI2 Cost: 2 Cardinality: 1
11 TABLE ACCESS BY INDEX ROWID SIPR.SRS_SCE Cost: 3 Bytes: 34 Cardinality: 1
10 INDEX RANGE SCAN SIPR.SRS_SCEI3 Cost: 2 Cardinality: 3
14 TABLE ACCESS BY INDEX ROWID SIPR.SRS_SCJ Cost: 1 Bytes: 24 Cardinality: 1
13 INDEX UNIQUE SCAN SIPR.SRS_SCJP1 Cardinality: 1
16 INDEX RANGE SCAN SIPR.CAM_SMOP1 Cost: 2 Bytes: 19 Cardinality: 1
18 INDEX UNIQUE SCAN SIPR.INS_SPRP1 Bytes: 12 Cardinality: 1 *** RESULT ***
COUNT(*)
83299I am still struggling to understand why this would have worked as to my knowledge the LOWER & UPPER functions are similar enough in function and regardless of that why would one version cause the optimiser to effectively ignore a join condition.
If anyone can shed any light on this for me it would be very much appreciated.
Regards,
Kieron
Edited by: Kieron_Bird on Nov 19, 2008 6:09 AM
Edited by: Kieron_Bird on Nov 19, 2008 6:41 AMMy mistake on the predicate information, was in a rush to run off to a meeting when I posted the entry...
*** UPPER Version of the Explain Plan ***
| Id | Operation | Name | Rows | Bytes | Cost | TQ |IN-OUT| PQ Distrib |
| 0 | SELECT STATEMENT | | 1 | 146 | 736 | | | |
| 1 | SORT AGGREGATE | | 1 | 146 | | | | |
| 2 | SORT AGGREGATE | | 1 | 146 | | 86,10 | P->S | QC (RAND) |
|* 3 | HASH JOIN | | 241 | 35186 | 736 | 86,10 | PCWP | |
|* 4 | HASH JOIN | | 774 | 105K| 733 | 86,09 | P->P | HASH |
|* 5 | HASH JOIN | | 12608 | 1489K| 642 | 86,08 | P->P | BROADCAST |
| 6 | NESTED LOOPS | | 14657 | 1531K| 491 | 86,07 | P->P | HASH |
|* 7 | HASH JOIN | | 14657 | 1359K| 490 | 86,07 | PCWP | |
|* 8 | HASH JOIN | | 14371 | 996K| 418 | 86,06 | P->P | HASH |
|* 9 | TABLE ACCESS FULL | SRS_SCE | 3211 | 106K| 317 | 86,00 | S->P | BROADCAST |
|* 10 | HASH JOIN | | 52025 | 1879K| 101 | 86,06 | PCWP | |
|* 11 | TABLE ACCESS FULL | MEN_MRE | 51622 | 1310K| 71 | 86,01 | S->P | HASH |
| 12 | INDEX FAST FULL SCAN| SRS_MSTP1 | 383K| 4119K| 30 | 86,05 | P->P | HASH |
| 13 | TABLE ACCESS FULL | SRS_SCJ | 114K| 2672K| 72 | 86,02 | S->P | HASH |
|* 14 | INDEX UNIQUE SCAN | INS_SPRP1 | 1 | 12 | | 86,07 | PCWP | |
| 15 | TABLE ACCESS FULL | MEN_MUA | 312K| 4268K| 151 | 86,03 | S->P | HASH |
| 16 | INDEX FAST FULL SCAN | CAM_SMOP1 | 527K| 9796K| 91 | 86,09 | PCWP | |
| 17 | TABLE ACCESS FULL | TEMP_WEBCT_USERS | 33276 | 194K| 3 | 86,04 | S->P | HASH |
Predicate Information (identified by operation id):
3 - access(UPPER("MUA"."MUA_EXTU")=UPPER("U"."LOGIN"))
4 - access("CAM"."AYR_CODE"="SCE"."SCE_AYRC" AND "CAM"."SPR_CODE"="SCJ"."SCJ_SPRC")
5 - access("MST"."MST_CODE"="MUA"."MUA_MSTC")
7 - access("SCE"."SCE_SCJC"="SCJ"."SCJ_CODE")
8 - access("SCE"."SCE_STUC"="MRE"."MRE_CODE")
9 - filter(SUBSTR("SCE"."SCE_AYRC",1,4)='2008' AND ("SCE"."SCE_STAC"='RCA' OR "SCE"."SCE_STAC"='RCE' OR
"SCE"."SCE_STAC"='RCI' OR "SCE"."SCE_STAC"='RCO' OR "SCE"."SCE_STAC"='RHL_R' OR "SCE"."SCE_STAC"='RIN' OR
"SCE"."SCE_STAC"='RLL' OR "SCE"."SCE_STAC"='RPD' OR "SCE"."SCE_STAC"='RSAS'))
10 - access("MST"."MST_CODE"="MRE"."MRE_MSTC")
11 - filter("MRE"."MRE_MRCC"='STU')
14 - access("SPR"."SPR_CODE"="SCJ"."SCJ_SPRC")
Note: cpu costing is off
40 rows selected.*** LOWER Version of the Explain Plan ***
| Id | Operation | Name | Rows | Bytes | Cost | TQ |IN-OUT| PQ Distrib |
| 0 | SELECT STATEMENT | | 1 | 146 | 736 | | | |
| 1 | SORT AGGREGATE | | 1 | 146 | | | | |
| 2 | SORT AGGREGATE | | 1 | 146 | | 88,10 | P->S | QC (RAND) |
|* 3 | HASH JOIN | | 257K| 35M| 736 | 88,10 | PCWP | |
|* 4 | HASH JOIN | | 774 | 105K| 733 | 88,09 | P->P | HASH |
|* 5 | HASH JOIN | | 12608 | 1489K| 642 | 88,08 | P->P | BROADCAST |
| 6 | NESTED LOOPS | | 14657 | 1531K| 491 | 88,07 | P->P | HASH |
|* 7 | HASH JOIN | | 14657 | 1359K| 490 | 88,07 | PCWP | |
|* 8 | HASH JOIN | | 14371 | 996K| 418 | 88,06 | P->P | HASH |
|* 9 | TABLE ACCESS FULL | SRS_SCE | 3211 | 106K| 317 | 88,00 | S->P | BROADCAST |
|* 10 | HASH JOIN | | 52025 | 1879K| 101 | 88,06 | PCWP | |
|* 11 | TABLE ACCESS FULL | MEN_MRE | 51622 | 1310K| 71 | 88,01 | S->P | HASH |
| 12 | INDEX FAST FULL SCAN| SRS_MSTP1 | 383K| 4119K| 30 | 88,05 | P->P | HASH |
| 13 | TABLE ACCESS FULL | SRS_SCJ | 114K| 2672K| 72 | 88,02 | S->P | HASH |
|* 14 | INDEX UNIQUE SCAN | INS_SPRP1 | 1 | 12 | | 88,07 | PCWP | |
| 15 | TABLE ACCESS FULL | MEN_MUA | 312K| 4268K| 151 | 88,03 | S->P | HASH |
| 16 | INDEX FAST FULL SCAN | CAM_SMOP1 | 527K| 9796K| 91 | 88,09 | PCWP | |
| 17 | TABLE ACCESS FULL | TEMP_WEBCT_USERS | 33276 | 194K| 3 | 88,04 | S->P | HASH |
Predicate Information (identified by operation id):
3 - access(LOWER("MUA"."MUA_EXTU")=LOWER("U"."LOGIN"))
4 - access("CAM"."AYR_CODE"="SCE"."SCE_AYRC" AND "CAM"."SPR_CODE"="SCJ"."SCJ_SPRC")
5 - access("MST"."MST_CODE"="MUA"."MUA_MSTC")
7 - access("SCE"."SCE_SCJC"="SCJ"."SCJ_CODE")
8 - access("SCE"."SCE_STUC"="MRE"."MRE_CODE")
9 - filter(SUBSTR("SCE"."SCE_AYRC",1,4)='2008' AND ("SCE"."SCE_STAC"='RCA' OR "SCE"."SCE_STAC"='RCE' OR
"SCE"."SCE_STAC"='RCI' OR "SCE"."SCE_STAC"='RCO' OR "SCE"."SCE_STAC"='RHL_R' OR "SCE"."SCE_STAC"='RIN' OR
"SCE"."SCE_STAC"='RLL' OR "SCE"."SCE_STAC"='RPD' OR "SCE"."SCE_STAC"='RSAS'))
10 - access("MST"."MST_CODE"="MRE"."MRE_MSTC")
11 - filter("MRE"."MRE_MRCC"='STU')
14 - access("SPR"."SPR_CODE"="SCJ"."SCJ_SPRC")
Note: cpu costing is off
40 rows selected.As you state something has obviously changed, but nothing obvious has been changed.
We gather statistics via...
exec dbms_stats.gather_schema_stats(ownname => 'USERNAME', estimate_percent => DBMS_STATS.AUTO_SAMPLE_SIZE , degree => 4, granularity => ''ALL'', cascade => TRUE);
We run a script nightly which works out which indexes require a rebuild and rebuild those only it doesn;t just rebuild all indexes.
It would be nice to be able to use the 10g statistics history, but on this instance we aren't yet at that version, hopefully we will be there soon though.
Hope this helps,
Kieron
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