Performance Tuning :: Returning All Rows That Equal Max (value)?
Oct 14, 2010
I'm trying to write a query that counts how many sessions are active during a 1 second time interval, then returns the maximum number of sessions active during any time interval, and all the time intervals that hit that max.
If a table(have a primary key) is empty(after truncate),the sql of dml(insert,update) is very quickly,but if the table have many rows about 10,000,000 rows, the dml is very slowly,why?
There is coulmn called DATA in a table with LONG RAW datatype. we are facing more than 60% chained rows in this table because of this LONG RAW column.
It is very difficult to clean up these chained rows periodically. Since an application using this table is a business critical interms of high availability.Hence, is there any other way in oracle to avoid chained rows permanently in future?
1) I have 5 Exported Dump files. 2) All of those 5 dump files were taken in different time periods. 3) Many of those Dump files are having the same Partition records.
eg:- Dump 1:- 01-06-2010 to 31-11-2010 Dump 2:- 01-09-2010 to 31-12-2010
4) Now i want to import all those partitioning data into a single table, without having any duplication.
Our application servers will be running a SELECT which returns zero rows all the time.This SELECT is put into a package and this package will be called by application servers very frequently which is causing unnecessary CPU.
Original query and plan
SQL> SELECT SEGMENT_JOB_ID, SEGMENT_SET_JOB_ID, SEGMENT_ID, TARGET_VERSION FROM AIMUSER.SEGMENT_JOBS WHERE SEGMENT_JOB_ID NOT IN (SELECT SEGMENT_JOB_ID FROM AIMUSER.SEGMENT_JOBS) 2 3 4 5 ; [code]....
Which option will be better or do we have other options?They need to pass the column's with zero rows to a ref cursor.
I am working on a script in which I want to retrieve multiple rows but I get error ORA-1422.I tried solving it using the following script , but it still gives error.
CREATE OR REPLACE PROCEDURE proc_query DECLARE TYPE all_dest IS TABLE OF NUMBER; destIds all_dest; BEGIN SELECT dest_id from sb_packet WHERE src_id = 32; RETURNING dest_id bulk collect into destIds; END;
I understand what the message "subquery returning multiple rows" means but I have a case where I'm not 100% sure why it's happening to my update query (which in turn probably means I don't fully understand what's going on behind the scenes)
Here is my query:
Update A set (A.id, A.alt_name, A.min_rank)= (SELECT B.id, B.fullname, MIN(B.nm_rankval) FROM B, A WHERE A.id = B.id AND A.name <> B.fullname AND B.nametyp = 'ON' GROUP BY B.id, B.fullname) ;
The subquery returns 6 rows but they are all unique in terms of the id, name, rankval, etc...I naturally thought that the update statement wouldn't have a problem with this since the subquery is returning rows that are not duplicates and match one for one between table A and B. I used the group by to ensure I return unique values from table B (which does have duplicate id values)
Each of those 6 rows from the subquery of table B can be matched 1-1 with table A...so what am I missing.
The following code is indicative of what I'd like to do (as in not correct at all ). Would there be a more immediate way to accomplish this other than executing a SELECT statement after the UPDATE?
-- Incorrect indicative example 1.
DECLARE v_cur SYS_REFCURSOR; BEGIN UPDATE table1(f1, f2) SET ('v1', 'v2') WHERE f3 = 'v3' RETURNING <updated_rows> INTO v_cur END;
-- Incorrect indicative example 2.
DECLARE v_cur SYS_REFCURSOR; BEGIN OPEN v_cur FOR UPDATE table1(f1, f2) SET ('v1', 'v2') WHERE f3 = 'v3' END;
This is a surprisingly common one I've found on the web...even on devshed forum
I am updating one table from another (Updating Table A from Table B):
Table A ID, Value -- ----- 1 A 1 A 2 B
Table B ID, Value -- ----- 1 Animal 2 Box
Table A (modified) ID, Value, Name 1 A Animal 1 A Animal 2 B Box
No I need to update a new column in Table A with the value in Table B.Value where the ID's from both tables match. Problem is: When I do this I get multiple rows and hence Oracle won't let me update this column. Now, I keep reading that for these types of updates, there has to be a one-to-one relationship...
Is this true...is there anyway of telling Oracle to update wherever it finds that ID, regardless of how many duplicate ID's there are?
This is quite a frustrating problem and most of the sites that I've looked for solutions try get the query one-to-one...problem is...with my table sets it's impossible to do that - I need to update wherever the id's match (even if it return multiple rows).
Looking 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?
I have two tables with 113M records in DWH_BILL_DET & 103M in prd_rerate_chg_que and Im running following merge query, which is running for 13 hrs to update records, which is quiet longer time.
SQL> explain plan for MERGE /*+ parallel (rq, 16) */ INTO DWH_BILL_DET rq USING (SELECT rated_que_rowid, detail_rerate_flag_code, rerate_sel_key,
How the length of column width effects index performance?
For example if i had IOT table emp_iot with columns: (id number, job varchar2(20), time date, plan number)
Table key consist of(id, job, time)
Column JOB has fixed list of distinct values ('ANALYST', 'NIGHT_WORKED', etc...).
What performance increase i could expect if in column "job" i would store not names but concrete numbers identifying job names. For e.g. i would store "1" instead 'ANALYST' and "2" instead 'NIGHT_WORKED'.
I 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?
There 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 ?
How many records could I have in a single table without performance degradation with Standard Edition without partitioning with cutting-edge server (8 or 12 cores, 72 GB RAM, FC 4 Gbit, etc...) and good storage?
300 Millions in only one table with 500K transactions / day is too much?
Testing 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?
I need to check the package performance and need to improve the package performance.
1. how to check the package performance(each and every statement in the package)? 2. In the package using the delete statement to delete all records and observed that delete is taking long time to delete all the records in the table(Table records 7000000). This table is like staging table.Daily need to clean the data before inserting the data into it. what can I use instead of Delete.
Somewhere 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.
When i exporting an user using expdp utility, the load the on the server is going up-to 5. The size of the database is 180GB. Below is the command that i use for export.
The following query gets input parameter from the Front End application, which User queries to get Reports.There are many drop down boxes like LOB, FAMILY, BRAND etc., The user may or may not select values from drop down boxes.
If the user select any one or more values ( against each drop down box) it has to fetch all matching values from DB. If the user does'nt select any values it has to fetch all the records, in this case application will send a value 'DEFAULT' (which is not a value in DB ) so that the DB will fetch all the records.
For getting this I wrote a query like below using DECODE, which colleague suggested that will hamper performance.From the below query all the variables V_ are defined in procedure which gets the values selected by user as a comma separated string here V_SELLOB and LOB_DESC is column in DB.
DECODE (V_SELLOB, 'DEFAULT', V_SELLOB, LOB_DESC) IN OPEN v_refcursor FOR SELECT /*+ FULL(a) PARALLEL(a, 5) */ * FROM items a WHERE a.sku_status = 'A'
what the principal things to look at when we have for the same query different performance results are?I have 2 different bases: the plan and data are the same but performance results are very differents.
are the most important performance keys we have to calculate or take in account to preserve or to increase the DB performance in terms of response times, and whatsoever according to performance ?
I would like to select test_sub.price as per the below conditions. If test_bb.value_date, test_bb.vehicle matches to test_sub.value_date,test_sub.vehicle then display test_sub.price
If there is no match then as above find the closest test_sub.value_date which is less than test_bb.value_date and select corresponding test_sub.price for the same vehicle combination.
begin insert into test_bb values(10,to_date('12-04-2012','dd-mm-yyyy')); insert into test_bb values(10,to_date('10-02-2010','dd-mm-yyyy')); insert into test_bb values(20,to_date('24-01-2014','dd-mm-yyyy')); insert into test_bb values(20,to_date('22-02-2008','dd-mm-yyyy')); end; /
begin insert into test_sub values(10,to_date('12-04-2012','dd-mm-yyyy'),2); insert into test_sub values(10,to_date('08-01-2010','dd-mm-yyyy'),4); insert into test_sub values(10,to_date('14-04-2014','dd-mm-yyyy'),6); insert into test_sub values(10,to_date('06-08-1947','dd-mm-yyyy'),8); insert into test_sub values(20,to_date('24-01-2014','dd-mm-yyyy'),10); insert into test_sub values(20,to_date('20-02-2006','dd-mm-yyyy'),12); insert into test_sub values(20,to_date('18-02-2004','dd-mm-yyyy'),14); insert into test_sub values(20,to_date('28-02-2006','dd-mm-yyyy'),16); insert into test_sub values(20,to_date('22-DEC-2007','dd-mm-yyyy'),19); end; /
I could write as below but I would like to know if there is a better way of doing it.
select bb.vehicle ,sub.price ,bb.value_date from test_bb bb ,test_sub sub where bb.vehicle=sub.vehicle [code].........
I am working on an application that allows a user to create a KPI formula, and the app dynamically creates a view for this formula. However as we started using it we have found that we are encountering the ORA-10476 (divisor is equal to zero) often. I have read about options of using decode or case to prevent this but it doesn't cover all our options. As a result of the fact that the user can create any equation he wants , and it can be as complicated as they want ( 2 examples:
A/(B/C-D/E) - If C or E or (B/C-D/E) are 0 the whole select will fall A/(B-C/(D-F)) - if (D-F) or ((B-C/(D-F)) is 0 then again the select will fall.
I have seen that in MS SQL they have an option of arithabort which allows the database to return the rows that don't fall under the "divisor by 0".
either by setting something similar to arithabort, or maybe a procedure to check an equation and return the arithmetical steps in order that athey are performed?
The below code gives me error (ORA-01476: divisor is equal to zero)
SELECT ((COUNT(DECODE(SUBSTR(A.ASSETNUM,6,3),'ACS','ACS',0,null))/COUNT(DECODE(SUBSTR(A.PMNUM,1,3),'ACS','ACS',0,null)))*100) FROM WORKORDER A WHERE TO_CHAR(A.REPORTDATE,'MON-YYYY') = :WO_DATE;
