When To Use A Reverse Key Index
Jul 3, 2012I've read some documentation about the reverse key indexes, but I haven't understood when really it can be useful use them. when it's smart to use them according to your experiences?
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Create Reverse Key Index On Table
Feb 25, 2013difference between the ways we create Reverse Key Index on the table.The two ways are as below:
1) CREATE INDEX <Index_Name> ON <Table_Name>(<Column_Name) REVERSE ;
2) CREATE INDEX <Index_Name> ON<Table_Name>(REVERSE(<Column_Name>)) ;
Which one is the appropraite one.
Are both going to act in the same way.
I created index in both ways one by one on the table.But when I fire the select statement against the same table, The explain plan doesn't show any cost and it shows the full table scan in both ways.The select statement used is as below...I want to compare the column with string RBO(i.e('RBO%') at the start.
SELECT *
FROM <Table_Name>
WHERE REVERSE (<Column_Name>) LIKE '%OBR' ;
The select statement is giving me the correct result. Only the explain plan is showing Full Table Scan.can we use this reverse with IN operator also in the same way by reversing the values.
SQL & PL/SQL :: Column Reverse In Record?
Nov 7, 2011I am trying to reverse data from couple record. I have display the output below of how I want it to be and is it possible to do it?
Quote:
This is how it is right now
ID|FROM_UOM_KEY|UOM_KEY|UOM|QUANTITY
1 |PK |PK |PK |1
2 |EA |PK |PK |3
3 |PK |PK |PK |1
4 |EA |PK |PK |3
I want it to be like this.
ID|FROM_UOM_KEY|UOM_KEY|UOM|QUANTITY
1 |EA |PK |PK |1
2 |PK |PK |PK |3
3 |EA |PK |PK |1
4 |PK |PK |PK |3
Here is the code
SELECT
from_uom_key,
vip.UOM_KEY,
--DECODE ( from_uom_key,from_uom_key,vip.UOM_KEY,from_uom_key),
[Code]....
PL/SQL :: Reverse Search In String
Aug 13, 2012I have table having a single column a, which contain the values "HP Laptop", can search it in either way , i mean to say either user input the HP Laptop or Laptop HP? is it possible via SQL query ?
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Mar 2, 2012The Text is displayed correctly when there is no "Arabic comma" ، , otherwise the text will be reversed, How can I avoid the issue, why we have such problem only when we add the comma. The screenshot: s10.postimage.org/8qw1l8621/Arabic_comma.png
View 3 Replies View RelatedSQL & PL/SQL :: Search String From The End To Beginning (reverse INSTR)?
Sep 22, 2010Trying to get a number out of an error backtrack
06512: at "SCHEMA.PROCEDURE", line 4
I only need to take the 4 out of this message. Of course the number might be anything from 1 to 10000.
The database languages might differ so I can't do this using
v_line_no:=SUBSTR(v_line_no,INSTR(v_line_no,'line')+5)
As it would not find any 'line' inside the string.
PL/SQL :: Reverse Update - Create Synonym In Different Schema
Aug 8, 2012I have table a in database 1 . Now i have created the MV for table a in database 2.
then i am going to create a synonym in different schema in the database 2.
Now i want to update the synonym in database 2 the same as to refresh in table a database 1.
How to achieve this??
SQL & PL/SQL :: Order Of Bytes Returned By Dump() Function In Reverse Key Indexes?
May 28, 2013Oracle Version: 11gR2: 11.2.0.1.0 - 64bit
OS: Linux Fedora Core 17 X86_64
Currently, I'm reading the online book Oracle Concepts, Chapter 3: 3 Indexes and Index-Organized Tables, section: Reverse Key Indexes in order to understand this topic.
As I understand for each pair of (key, rowid) in the index structure, the rowid for each row in the table obviously remains the same but the bytes of the key are reversed before the key is stored. So for example on a 32 bit machine (just an example) a key = 10 AB CD EF will be stored as FE DC BA 01 , am I right?
According to the documentation, this becomes interesting in RAC environments in order to remove a hot spot from the index (when multiple instances repeatedly modify the same block) with the disadvantage that in some cases there cannot be Index Range Scan any more as data in the index is not sorted by column key when it is stored.
I was just curious to see how bytes of each key are reversed and after a bit googling I found an article where Tom Kyte shows with an example by using dump function (which as I understand gives the internal representation of a given expression) the difference in the sequence of bytes. Here is the link
[URL]
So based on his instructions I tried to do my own test, yet I don't get the same result, that is, the bytes are not reversed for me once we rebuild the index by REVERSE key word.
I'm going to write down here the test that I did, where is/are my error(s)
Test Case:
(I use a copy of the employees table in hr sample schema)
SQL> CREATE TABLE emp_test AS SELECT * FROM hr.employees;
Table created.
SQL> CREATE INDEX emp_test_idx ON emp_test(first_name);
[code]...
Now, a test SQL Query using the index we've just defined (just for giving an example)
SQL> SELECT first_name,
2 dump(first_name, 16) as dump_result
3 FROM emp_test
4 WHERE first_name = 'Kelly';
FIRST_NAME DUMP_RESULT
-------------- ----------------------------------
Kelly Typ=1 Len=5: 4b,65,6c,6c,79
[code]...
So, according to the above Execution plan, Oracle does an Index Range Scan using the index that I defined on my table that is, emp_test_idx. According to the output of dump, the key (first_name) in that index is stored (in terms of bytes) as 4b,65,6c,6c,79
SQL> SELECT chr(to_number('4b', 'xx')) ||
2 chr(to_number('65', 'xx')) ||
3 chr(to_number('6c', 'xx')) ||
4 chr(to_number('6c', 'xx')) ||
5 chr(to_number('79', 'xx')) first_name
6 FROM DUAL;
FIRST_NAME
--------------------
Kelly
Which as we can see corresponds to the first name 'Kelly', the first name we specified in the above SQL query.
Now let's rebuild the index
SQL> ALTER INDEX emp_test_idx REBUILD REVERSE;
Index altered.
SQL>
Once the index keys have been reversed, I run the very same query in order to see the difference
SQL> SELECT first_name,
2 dump(first_name, 16) as dump_result
3 FROM emp_test
4 WHERE first_name = 'Kelly';
[code]...
So the second time after the index has been reversed, I still get the very same sequence of bytes, that is, 4b,65,6c,6c,79, whereas I expected to get 79,6c,6c,65,4b (that is, the reversed order of the initial bytes sequence)
Text :: Index For Domain Index With Composite Domain Index (CDI) Very Slow
Jun 27, 2012I am on 11.2.0.3 Enterprise Edition. We are using the new feature "Composite Domain Index" for a Domain index on a very large table (>250.000.000 rows). It really works with mixed queries. We added two number columns using FILTER BY.We have lots of DML on this table. Therefore, we are executing synchronize and optimize once the week. The synch behaves pretty normal. But "optimize_index" takes a very very long time to complete. I have switsched on 'logging' for the optimize process. The $I table takes some time but is finished normally. But the optimization of the $S table (that is the table created for the CDI feature) is running over 12 hours now - and far from being finished. From the logfile, I can see that it optimizes 1000 rows every 20 minutes. Here is the output of the logfile:
Oracle Text, 11.2.0.3.0
14:33:05 06/26/12 begin logging
14:33:05 06/26/12 event
14:33:05 06/26/12 process $N for optimize: SEQDEV.GEN_GES_DESCRIPTION_CTX_I
14:33:16 06/26/12
14:33:16 06/26/12
[code]....
I haven't found a recommendation from Oracle not to use "optimize_index" for Domain Indexes with CDI. But in my case, it would be much faster just to drop and recreate the Domain Index in question.
Performance Tuning :: Local Index Versus Global Index On Partitioned Table
Jun 28, 2011I 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.
View 6 Replies View RelatedServer Administration :: Convert Global Index To Local Index
Jun 23, 2011I have a global index and I want to convert it to local index.Is there a way to recreate local index with out dropping the global index.
I can create a local index first and then drop the global index. But is there a way to create it with out dropping the global index, just convert it.
SQL & PL/SQL :: ORA-01502 - Index Or Partition Of Such Index Is In Unusable State?
Nov 29, 2010I am facing the error "ORA-01502: index or partition of such index is in unusable state " while loading the text data using
sql loader with direct path (direct = Y ,rows = 10000) option. Table consists an composite non unique index. If I query the dba indexes for the effected index it shows the index status as VALID. There was no maintaince done on the effected table or index. I have tried loading the same data using conventional path but didn't found any issues for the same.
Performance Tuning :: Index With NVL / Query Is No Longer Using Index
Nov 19, 2010I have a query which had a join:
a.c1=b.c1 and a.c2=@var
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?
Performance Tuning :: Force Index If Table Not Using Index?
Aug 9, 2013How to force an index if the table not using the index?
View 10 Replies View RelatedWhen Index Lock Contention Occurs / How To Know Which Index Is Causing
Aug 27, 2012We have occurrences of enq : TX - index contentions in the database. Using the SQL ID, we have identified the INSERT statement and the table which they are trying to insert.
This table has almost 25 different indexes, some of which are unique as well.I am wondering how to identify the actual index causing issue, out of these 25 indexes.
Is there any way to pin point to the name of index which is causing the lock?My plan is, once the index is identified, I would like to check the extents and inittrans and other attributes of this index to fix.
SQL & PL/SQL :: Create Non-cluster Index On A Clustered Index?
Jul 11, 2012Can we create non-cluster index on a clustered index?
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Aug 3, 2010Any on give explanation for difference between Index and Clustered Index?
It will be great if i get explanation how memory allocation and Execution takes place.?
Performance Tuning :: Difference Between Index Rebuild And Index Rebuild Online?
Jan 10, 2011What is the difference between index rebuild and index rebuild online.
View 3 Replies View RelatedPL/SQL :: Index Range Scan And Table Access By Index Rowid Versus Table Access Full
Oct 5, 2013Let'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
Last Used Time Of Index
Apr 7, 2011I'm using Oracle 11g and I have a bunch of indexes and I want to check if they are being used. I just ran my workloads and now I want to see when each one was last used so I can see if it was during my timeframe or not.
After I ran my test, I found the below, but since I did not enable this, plus I have many indexes.
--Monitor an index to see if it's used
alter index SAMPLE_INDEX monitoring usage;
select * from v$object_usage where index_name = 'SAMPLE_INDEX';
alter index SAMPLE_INDEX nomonitoring usage;
Index With Degree More Than 1
Jul 29, 2010There is an index with degree 16 on a rac env. The base table has no degree. The table and index are not partitioned. Does the degree of index only affect index DDL (alter, rebuild etc)? Any effects on query (PQ)?
View 4 Replies View RelatedIndex In Cache
Apr 21, 2013i have a application which uses 32 tables for retrieval in this 4 tables are important and have a size more than 100 mb can i move the index of these 4 tables cache memory to improve the applications retrieval performance if i done so ,then that will affect any other applications performance
View 1 Replies View RelatedSQL & PL/SQL :: Index And Group By
Sep 5, 2012I have a query that extracts the row with a max(record_date) within a group.
select ssn, fund, type_indicator, annuitant, cur_year, record_date, guarantee
from LC_MORTALITY
where (ssn, fund, type_indicator, annuitant, cur_year, record_date) in
(select ssn, fund, type_indicator, annuitant, cur_year, max(record_date)
from LC_MORTALITY
group by ssn, fund, type_indicator, annuitant, cur_year);
the table has index that matches the group by clause exactly.
create index IDX_LC_MORTALITY_sftayd on LC_MORTALITY
(SSN,
FUND,
TYPE_INDICATOR,
ANNUITANT,
cur_year,
record_date
However, the plan ignores the index
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1963K| 241M| | 1375K (4)| 05:21:04 |
|* 1 | HASH JOIN RIGHT SEMI| | 1963K| 241M| 9701M| 1375K (4)| 05:21:04 |
| 2 | VIEW | VW_NSO_1 | 145M| 8038M| | 241K (12)| 00:56:22 |
| 3 | HASH GROUP BY | | 145M| 8038M| | 241K (12)| 00:56:22 |
| 4 | TABLE ACCESS FULL| LC_MORTALITY | 145M| 8038M| | 219K (3)| 00:51:13 |
| 5 | TABLE ACCESS FULL | LC_MORTALITY | 145M| 9840M| | 222K (5)| 00:51:49 |
---------------------------------------------------------------------------------------------
[code]...
It uses the index but still shows "table access full" in one place. Why is there still a full access?Can I do anything to optimize further?
SQL & PL/SQL :: Use Of Table Index?
Feb 10, 2012Am pasting the sample code here, which i got from some site..
DECLARE
TYPE population_type IS TABLE OF NUMBER INDEX BY VARCHAR2(64);
country_population population_type;
continent_population population_type;
howmany NUMBER;
[code]...
Here we are fetching indexes (like Antartica/Australia) from these two statements continent_population.FIRST or continent_population.LAST. If there are three or more indexes in the same table, how to fetch all of them?
I have tried using this, but doesnt work because loop variables are by default integers:
for i in continent_population.FIRST .. continent_population.LAST loop
dbms_output.put_line('i:'||i);
end loop;
SQL & PL/SQL :: Explicit Name For Index Of IOT
Feb 18, 2011Need some Clarification on the below query:
Can we specify explicit name for the index of the IOT.
SQL & PL/SQL :: How To Rename A Index
Aug 8, 2011How can i rename a index? is there a way except for drop and create.
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May 19, 2011How can i turn this into functional index.
WHERE (IPC_DISP_ID IS NOT NULL AND DISP_EXIST > 0)
AND (IPC_UPU_BCD IS NOT NULL AND RECPT_EXIST > 0)
AND ( (IPC_ITM_ID IS NOT NULL AND ITM_EXIST > 0) OR IPC_ITM_ID IS NULL )
SQL & PL/SQL :: Delete An Index
Jun 27, 2010I have a very huge table. There are many indexes.My focus is on the following indexes:
APT_DEDUCTIBLE A_PT_ORDREGBUS_UNIT
APT_DEDUCTIBLE A_PT_ORDREGMD_CODE
APT_DEDUCTIBLE A_PT_ORDREGPT_CODE
[Code]...
My Question is, since this 3 indexes has two columns "Bus_unit and Md_code", which index can i delete. Will they effect on database performance, if i delete one of them?
PL/SQL :: Index Not Being Used In Group By
Sep 14, 2012Here is the scenario with examples. Big table 333 to 500 million rows in the table. Statistics are gathered. Histograms are there. Index is not being used though. Why?
CREATE TABLE "XXFOCUS"."some_huge_data_table"
( "ORG_ID" NUMBER NOT NULL ENABLE,
"PARTNERID" VARCHAR2(30) NOT NULL ENABLE,
"EDI_END_DATE" DATE NOT NULL ENABLE,
"CUSTOMER_ITEM_NUMBER" VARCHAR2(50) NOT NULL ENABLE,
"STORE_NUMBER" VARCHAR2(10) NOT NULL ENABLE,
"EDI_START_DATE" DATE,
[Code]...
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> SELECT num_rows FROM user_tables s WHERE s.table_name = 'some_huge_data_table';
NUM_ROWS
----------
333338434
SQL> SELECT MAX(edi_end_date)
2 FROM some_huge_data_table p
3 WHERE p.org_id = some_number
4 AND p.partnerid = 'some_string';
MAX(EDI_E
---------
13-MAY-12
Elapsed: 00:00:00.00
SQL> explain plan for
2 SELECT MAX(edi_end_date)
3 FROM some_huge_data_table p
4 WHERE p.org_id = some_number
5 AND p.partnerid = 'some_string';
Explained.
SQL> /
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
Plan hash value: 2104157595
--------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 22 | 4 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 22 | | |
| 2 | FIRST ROW | | 1 | 22 | 4 (0)| 00:00:01 |
|* 3 | INDEX RANGE SCAN (MIN/MAX)| some_huge_data_table_PK | 1 | 22 | 4 (0)| 00:00:01 |
--------------------------------------------------------------------------------------------
SQL> explain plan for
2 SELECT MAX(edi_end_date),
3 org_id,
4 partnerid
5 FROM some_huge_data_table
6 GROUP BY org_id,
7 partnerid;
Explained.
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
Plan hash value: 3950336305
-------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 44 | 1605K (1)| 05:21:03 |
| 1 | HASH GROUP BY | | 2 | 44 | 1605K (1)| 05:21:03 |
| 2 | TABLE ACCESS FULL| some_huge_data_table | 333M| 6993M| 1592K (1)| 05:18:33 |
-------------------------------------------------------------------------------
Why wouldn't it use the index in the group by? If I write a loop to query for different partnerid (there are only three), the whole things takes less than a second.
btw, I gave the index hint too. Didn't work. Version mentioned in the example.
Index On Partitioning Key
Mar 13, 2012There is a very large fact table that is range partitioned by a column DATE_KEY of type NUMBER(38), such that every hour is a different partition. There is a bitmap index BX$FACT#DATE_KEY on field DATE_KEY, which also is a foreign key referencing DATE_DIM (DATE_KEY). There is a different DATE_KEY for every hour, generated as YYYYMMDDHH24.
When I run
"SELECT * FROM FACT WHERE DATE_KEY >= 2012031207 AND DATE_KEY < 2012031208"
to get all the records for 7 am on March 12th, partition pruning kicks in and sees that only one partition is used. The CBO then decides to do a full scan of the partition. This behavior is correct/desired.
If, however, I run
"SELECT * FROM FACT WHERE DATE_KEY = 2012031207 AND DATE_KEY < 2012031209"
to get all the records for 7 and 8 am, Oracle knows that it will have to scan two partitions. The CBO then decides that using the BX$FACT#DATE_KEY must be a good idea and, instead of doing a full scan of the partitions, does access by local index rowid, which is many times slower.
I think I understand the cause - when more than a single partition is involved, Oracle has to use the global index stats (instead of the local ones, like in the first scenario) and the CBO decides to use it because that the selectivity for the global index is great, when in fact the query will return all the rows for that particular partition (no selectivity).
How to get the CBO to choose a full scan in the second scenario as well? I need to support ad-hoc queries generated by a BI tool, so I cannot add hints to the queries. I also can't get rid of the index on DATE_KEY, because in real life the predicates are on fields of the date dimension, not directly on the key, so I need to join on it.