Performance Tuning :: Full Table Scan - Query Without Where Clause?
Jul 11, 2013
Below query is degrading the performance of database. As we know that, without where clause, query do full table scan.Now, it is written to generate the sequence no.
SQL> explain plan for
2 SELECT NVL(MAX(P.NUM_SERIAL_NO), 0) + 1 FROM CNFGTR_IRDA_ENVELOPE_DTLS P
3 /
Explained.
SQL> select * from table(dbms_xplan.display());
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
Plan hash value: 3345343365
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------------------------
I have created an non unique index lk_fein on lookup_fein( code,map_id,trash). When I check the explain plan it does a full table scan on lookup_fein. if I force it to use index by it does and the cost also decreases.
I�m Using Oracle 11.I have a table with 16 million rows and an index (let's call it the employee table with an index on department). I need to select all the employees whose departments are located in the uk. I achieve this by selecting all the department numbers from departments where location = 'UK' in a sub select then plug this into the main query as follows:
SELECT * FROM employees WHERE department IN (SELECT department from departments where location = 'UK');
It takes ages, 25 seconds or more, the explain plan shows its doing a full table scan on emplyees. I need it to use the index. The sub query is instant and returns only 5 rows. If I explicitly put the 5 numbers in the IN clause the query uses the index and executes in 0.04 seconds. See below:
SELECT * FROM employees WHERE department IN (1,2,3,4,5);
I need it to use the subquery once and then use the index on the main table.
There is a table in Database with millions of records and a query --- Select rowid, ANI, DNIS, message from tbl_sms_talkies where rownum<=:"SYS_B_0" ---- using the high CPU and also this query having high number of executions.
I want to make full table scan of my query so that I can execute it using parallel option & the query will get completed in few mins. Even though I used this hint "/*+ parallel(t2,4) full(t2) */, the query is executing with 8 parallel processes but it is going for "Rowid Range Scan" and it is taking more time to complete. How to make this query to go for full table scan instead of "Rowid Range Scan" so that this query can be tuned.
SELECT /*+ parallel(t2,4) full(t2)*/ID, COUNT (1) FROM acnt_transact t2 GROUP BY ID;
I am rebuilding some UNUSABLE local index partitions on Oracle 8.1.7.4.0 (64bit) database . The platform is a HPUX machine.
The DDL of the partition table/indexes: ========================= CREATE TABLE TESTME ( INST_NO CHAR(3) NOT NULL, ACCT_NO CHAR(16) NOT NULL, REC_NO CHAR(9) NOT NULL, TRAN_TYPE CHAR(2) DEFAULT ' ', STAT CHAR(2) DEFAULT ' ', [code]...
I am adding condition in color to my existing query but my query taking too long time after that. This condition calculates last 3 month end dates from given COB (20110516).
SUMMARY is my summarized table and COB is my reference table
Without adding condition in query it gives INDEX (RANGE SCAN)--PK_SUMMARY(INDEX(UNIQUE)) After adding condition in query it gives INDEX(FAST FULL SCAN)--PK_SUMMARY(INDEX(UNIQUE))
how can i keep RANGE SCAN even after adding my new conditions?
SELECT distinct COB.COB_ID_C, SUMMARY.SUMM_COB_ID_C FROM
In the link below [URL] Thomas kyte has said, use the CBO and select /*+ FIRST_ROWS */ primary_key from table where rownum = 1; it'll read the index and stop at the first row. very fast on a big empty table (as the index is small and empty).
very fast on a big full table as the index is just read to find the first leaf node and then "stop".
It gives faster result if the primary key is used. But what if we have a table with around 1000 million rows and for the predicates there is a index range scan on the table.
What if we have a table say big_table (10000000000 rows) and the sql is something like
select /*+ first_rows */ 1 /* id, attribute_id*/ from big_table where attribute_name ='Gross Premium' and value ='10000' and version_date is null and rownum=1; --it's taking around 3 min
We observed that in such case there will be a range index scan for the index on the predicates. For a particular id there may be different values for attribute 'Gross Premium' and may have multiple versions.
How I would tune such a query where the purpose is to check if at least 1 records exists in the table for the input?
I was confused by partitioed table, when i select a partition of table, how does oracle to scan blocks? it scan all blocks of table or scan a single partition blocks only?
SQL> Explain Plan For 2 Select Count(1) From Tb_Hxl_List Partition(p_L3);
SELECT DISTINCT EXPOSURE_REF FROM KBNAS.VW_EXPOSUREDETS_FOR_CCYREVAL WHERE EXPOSURE_CURRENCY='THB' AND BASE_TXN_CCY='USD' AND BRANCH_CODE='7000' AND (REVAL_STATUS='O') AND CONV_RATE<>'62' AND (EXPOSURE_AMOUNT<>0) UNION SELECT DISTINCT ED.EXPOSURE_REF FROM KBNAS.EXPOSURE_DETAILS ED, [code].....
I have attached DDL for table EXPOSURE_DETAIL(PARTITION),LEDGERCARD,LEDGERCARDDETAILS, DDL for INDEX on those tables and DDL for Views..
Issue: we have created the Indexes but when we check the explain plain .. full table scan is going on..I have attached the explain plan ..
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.
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'
When i run a script that does a select from a single table (table has 33521868 records)the query is executed in about .094 seconds. I use the exact same query to insert into a temporary table and the query takes 10 minutes and more.
What should I be doing to speed up this process. Also tried using hints and it does not speed up the insert.
The requirement is I have to get the details of all data of previous Active cycle(status A) when the Item became disabled(status = D) for Input date.
In above case,since for Item P1 and on cycle date 04-Nov-12,status is D,I have to consider the previous active cycle which is 03-Nov-12. Based on above std date,the data is queried from another table to get all the Items. Item P2 should not be considered in above case.
Below is the code which I have written which considers the rundate as Input parameter.
-- To get the Items disabled for Input date with Itemdisabled as ( select item,stddate maxcycledate from Item_tbl where rundate = stddate
[code]....
In above case,I'm querying the Item_tbl twice once for getting the disabled Items and once for getting the Previous cycle which is active.
Is there any way to query above only once and get the required results using Lag/Lead functions etc.
How do i find a particular SQL or a set of SQL's which are excuted against a table (user identified table) that is either a very frequently executed query against that table or high impact SQL against that table? I am currently looking through the AWR reports to go through all the queries but i was wondering if there are any dictionary views where we can find this info from?
we have a situation where both undo tablespaces were almost filled i.e UNDOTBS1 99% and UNDOTBS2 100% filled so i add data files to it and then i found a lot of blocking session and was just killing them through EM then i stop my front end listener and also down the service, now i don't have any blocking session but on EM a big WAIT is coming. alert log shows nothing serious, it was showing deadlock but now it is over as well.
avoid duplication of **where** clause in my query.
In my below query, **JOIN** condition is same for both the queries and **WHERE** condition also same except this clause "and code.code_name="transaction_1" In **IF ** condition only credit and debit is swapped on both queries, due to this **Credit and Debit** and this where clause "and code.code_name="transaction_1" I am duplicating the query. avoid this duplication. I am using oracle 11g
SELECT day AS business_date, SUM(amount) AS AMOUNT, type_amnt AS amount_type,
high number of executions of specific types of queries which is using only rownum clause. For exam.
select ani, rowid from tbl_smschat_upuor where rownum<=:"SYS_B_0";
DB is having high number of executions of these type of queries and these when I m checking the execution plan for the same type of queries it is accessing the full table scan.
======================execution plan for above query 1000 rows selected. Execution Plan ---------------------------------------------------------- Plan hash value: 91289622 --------------------------------------------------------------------------------
Let's consider such table that all rows fit into single block:
SQL> create table test as select rownum id, '$'||rownum name from dual connect by level <= 530; Table created. SQL> create index i_test on test(id); Index created. SQL> SQL> begin
[code].....
why does approach with full scan take longer even if table occupies only one data block? PS. 11gR2
In my below query example , i have to pass more than 4000-5000 paramter in "a1.num" in below query. what is the best way to handle this, also if I pass more than 2000 paramter , the query takes a long time to execute. How can we solve the performance issue as well how I can pass more parameter.
How to avoid sort operation by an order by clause without changing the sort area size.what hints or changes should be done in query so that order by clause work faster.
I came across situation where a Nullable column is not using index for 'order by' clause. I added Not Null condition in the 'where' condition but it wasn't useful. I don't wanted to make composite index with not nullable column or with constant or modify column to 'Not Null'
So I carried out test cases and during which I found that in one case the sql statement does 'fast full scan' for data access but does not use index for 'order by' sorting
here are the steps
Initially I kept the column Nullable
SQL> create sequence s5; Sequence created.
SQL> create table t5 as select s5.nextval id,a.* from dba_objects a where rownum<1001; Table created.
SQL> set pages 100 SQL> select column_name,nullable from user_tab_columns where table_name='T5';
Misses in library cache during parse: 1 Optimizer mode: ALL_ROWS Parsing user id: 5
Rows Row Source Operation ------- --------------------------------------------------- 1000 SORT ORDER BY (cr=16 pr=0 pw=0 time=4771 us) 1000 TABLE ACCESS FULL T5 (cr=16 pr=0 pw=0 time=1157 us)
Elapsed times include waiting on following events: Event waited on Times Max. Wait Total Waited ---------------------------------------- Waited ---------- ------------ SQL*Net message to client 68 0.00 0.00 SQL*Net message from client 68 49.49 49.72 ********************************************************************************
select /*+ index(t i5) */ * from t5 t where id is not null order by id
Misses in library cache during parse: 1 Optimizer mode: ALL_ROWS Parsing user id: 5
Rows Row Source Operation ------- --------------------------------------------------- 1000 TABLE ACCESS BY INDEX ROWID T5 (cr=150 pr=0 pw=0 time=5167 us) 1000 INDEX FULL SCAN I5 (cr=71 pr=0 pw=0 time=3141 us)(object id 4673065)
Elapsed times include waiting on following events: Event waited on Times Max. Wait Total Waited ---------------------------------------- Waited ---------- ------------ SQL*Net message to client 69 0.00 0.00 SQL*Net message from client 69 22.89 28.04
Now I modified the 'id' column to Not Null
SQL> alter table t5 modify id not null;
SQL> set pages 100 SQL> select column_name,nullable from user_tab_columns where table_name='T5';
COLUMN_NAME N ------------------------------ - ID N OWNER Y OBJECT_NAME Y SUBOBJECT_NAME Y OBJECT_ID Y DATA_OBJECT_ID Y OBJECT_TYPE Y CREATED Y LAST_DDL_TIME Y TIMESTAMP Y STATUS Y TEMPORARY Y GENERATED Y SECONDARY Y
Misses in library cache during parse: 1 Optimizer mode: ALL_ROWS Parsing user id: 5
Rows Row Source Operation ------- --------------------------------------------------- 1000 SORT ORDER BY (cr=16 pr=0 pw=0 time=2398 us) 1000 TABLE ACCESS FULL T5 (cr=16 pr=0 pw=0 time=1152 us)
Elapsed times include waiting on following events: Event waited on Times Max. Wait Total Waited ---------------------------------------- Waited ---------- ------------ SQL*Net message to client 68 0.00 0.00 SQL*Net message from client 68 37.74 37.91 ********************************************************************************
Misses in library cache during parse: 1 Optimizer mode: ALL_ROWS Parsing user id: 5
Rows Row Source Operation ------- --------------------------------------------------- 1000 TABLE ACCESS BY INDEX ROWID T5 (cr=150 pr=0 pw=0 time=4166 us) 1000 INDEX FULL SCAN I5 (cr=71 pr=0 pw=0 time=3142 us)(object id 4673065)
Elapsed times include waiting on following events: Event waited on Times Max. Wait Total Waited ---------------------------------------- Waited ---------- ------------ SQL*Net message to client 68 0.00 0.00 SQL*Net message from client 68 8.28 8.45
Misses in library cache during parse: 1 Optimizer mode: ALL_ROWS Parsing user id: 5
Rows Row Source Operation ------- --------------------------------------------------- 1000 SORT ORDER BY (cr=6 pr=0 pw=0 time=1342 us) 1000 INDEX FAST FULL SCAN I5 (cr=6 pr=0 pw=0 time=1093 us)(object id 4673065)
Elapsed times include waiting on following events: Event waited on Times Max. Wait Total Waited ---------------------------------------- Waited ---------- ------------ SQL*Net message to client 68 0.00 0.00 SQL*Net message from client 68 1.88 1.89
Questions are
1) Why adding 'where id is not null wasn't enough for the index to get used in 'order by'? 2) While we got 'fast full scan' why index wasn't used for 'order by' clause? 3) Do we need the indexed column in where clause for being used in 'order by clause' too? 4) Do we need 'order by' clause if we are selecting only the indexed column with sequence generated values?
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?
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.
