Performance Tuning :: How To Verify If A Row Exists (index Range Scan)
Oct 18, 2011
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 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 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
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 created table Rang pertitionned, and List subpartitionned. My table is Interval partitionning. My subpartition is template based as is :
PARTITION BY RANGE ( DINFOIDENTITE ) INTERVAL ( (NUMTOYMINTERVAL(1,'MONTH')) ) SUBPARTITION BY LIST ( AVANT_DERNIER_MATCLE )
[Code]....
i would have the same repartition with 10 differents tablespaces, one for each subpartition.
I search on Oracle documentation this morning, but the only thing i've found is that this option is possible with the STORE IN clause, but only for HASH partitionning.
Is there a way to specify STORAGE clause with a template for my indexes ?
I have a query that seems to repeatedly call an index scan on a table for reasons I'm not sure about. Why it would be doing the index scan on totaldwellingarea in the dimensions table (DIMEN_PID_TDWELLAREA) repeatedly? This only seems to happen when I put on the range clause d.totaldwellingarea between scr.lowvalue and scr.highvalue.
I am using Oracle version 9.2.0.3.
select d.propertyid,d.totaldwellingarea, e.size_, scr.size_ from eqid e, dimensions d, brt_eval.size_code_ranges scr where e.style not in ('1','A','G','L') and e.size_ = '0' and d.propertyid = e.propertyid and e.style = scr.style and d.totaldwellingarea between scr.lowvalue and scr.highvalue;
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
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 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);
I have a huge table (about 60 gb) partition over range. The index on this table is global index created on 4 columns together. I have a query which is running very slowly. The explain plan is showing the use of this global index.Explain plan is not showing pstart and pend because the index is global.
where @var is user supplied input at runtime...We had a index on a.c2 . The CBO would use this index to generate an opitimised query plan.We found some records from table "b" were dropping due to inner join. So we made a change in join. It'd be like
a.c1(+)=b.c1 and nvl(a.c2,@var)=@var
This query is no longer using the index, instead its doing a full table scan causing the query to slowdown.I have tried creating index on nvl(a.c2,'31-dec-9999')
But the CBO won't use it.Anyway to create index on this col so that full table scan can be avoided?
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'.
here we have an scenario where we want to find out all the sql statements that are executed in a particular time. The sql statements are executed via our application. I tried in awr report but it shows only the sql query which has taken long time to execute. and i even tried in V$session and V$sqlarea. how to view the executed sql statements in a particular session/current session
As per Article mentioned in Oracle Base,I have converted non-partitioned table (1 million data) into range-partition table,but,I don't see performance improvement in explain .
We have a DELETE statement when coming from application is not using index but when run from Toad or SQLplus as same user uses index. Explain plan also shows using index.I did a query on v$sql below is the output of the query( I have attached the same as a txt file). All the stats are up to date and confirmed from the developer the variable B1 is using the same datatype as column MAXMKY.
SQL_TEXTSQL_ID DISK_READSOPTIMIZER_HASH_VALUE DELETE LOTA WHERE MAXMKY=:B1 2g2prrp3z56ah19,099,1891,846,735,884 DELETE LOTA WHERE MAXMKY=:B1 2g2prrp3z56ah0 1,846,735,884 OPTIMIZER_COST HASH_VALUEPLAN_HASH_VALUE MODULEPARSING_SCHEMA_NAME
I am working on a query for a feedback response system which is going to be targeted at the common case when the user only want the most recent 10-20 rows in the feedback table. My though is to create an index on the date column, do a sort in an inner query and rownum <= in an outer query. This works as I expect when I am only querying the main table (lookup by index with a stop key), but when I start joining the main table to attribute tables I end up with a full table scan of the main table with the stop key applied after all the joins are completed, the index is nowhere to be found.
CREATE TABLE attr1_tbl(attr1_id NUMBER NOT NULL, attr1 VARCHAR2(10) NOT NULL, CONSTRAINT attr1_pk PRIMARY KEY (attr1_id)); CREATE TABLE attr2_tbl(attr2_id NUMBER NOT NULL, attr2 VARCHAR2(10) NOT NULL, CONSTRAINT attr2_pk PRIMARY KEY (attr2_id)); CREATE TABLE attr3_tbl(attr3_id NUMBER NOT NULL, attr3 VARCHAR2(10) NOT NULL, CONSTRAINT attr3_pk PRIMARY KEY (attr3_id)); [code]....
One thing I noticed was that when no data is selected from the attribute tables, even if they are joined in the query, the CBO throws them out of the plan and only accesses the main table. With the foreign keys this makes sense and really just disqualified my first thought that maybe I was missing a foreign key or not null constraint somewhere.
I also added the cardinality hint to overcome the chance that in my test case there was so little data that index access is not worth it.
* 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 ;
I have the following problem. When I used in the IN-Statement fixed values e.q. 197321,197322,197323 ..., the index i_tab2_index works fine (index range scan).
But when I used in the IN-Statement an Sub-Select, the index i_tab2_index doesn't work (fast full scan)!My scale indices and used Selects:
CREATE INDEX i_tab1_index ON tab1 ( datum, flag_inst ); CREATE INDEX i_tab2_index ON tab2 ( tab2Idx, kontro ); SELECT count(epidx) as rowAnz FROM tab2 WHERE tab2Idx IN ( SELECT tab1IDX FROM tab1 WHERE datum BETWEEN '20120117' AND '20120117' AND flag_inst = '1' ) AND kontro = '9876521' [code]...
get all the unused index in the system , if i put this query in batch job and execute it every night upto one months and store its data in a table and after one months i can get all the used indexes and left would be our unused indexes.
select distinct p.object_name c1 from dba_hist_sql_plan p, dba_hist_sqlstat s
I have a table whose size is 2.3 GB and there are two indexes on it. One index is based on a Date column whose size is 900 MB, and the Other index consists of 5 columns including the date column, and the size is almost 2GB. But when i query the table using the Date column, it is doing a range scan on the second index which is almost the same size as the table. why is it not using the first index? What steps should i take so that it uses the First index without passing hints.
mbr has 60,000 rows and member has 60,000 rows approx. two tables have indexes on ssn, and citi_no on them.
PK of mbr : mbr_id PK of member : mbr_id
other columns are not PK, and have no index on it.
I'm wondering why the statment doesn't use index while ssn and citi_no have index.
MERGE INTO mbr t USING (SELECT mbr_id,citi_no FROM member) a ON (t.ssn = a.citi_no) WHEN MATCHED THEN UPDATE SET t.asis_mbr_id = a.mbr_id where t.ssn not in(select ssn from mbr group by ssn having count(*) > 1)
I have to create indexes on foreign key columns ,now if composite index is already there with foreign key column then that will work or i will have to create a single column index.
