SQL & PL/SQL :: Hash Join And Nested Loops
Mar 16, 2011What is the difference between Hash join and Nested Loops in pl / sql?
View 1 Replies
ADVERTISEMENT
Performance Tuning :: NESTED LOOPS JOIN And Distributed Operations?
Oct 30, 2012 I want to make sure I am describing correctly what happens in a query where there is distributed database access and it is participating in a NESTED LOOPS JOIN. Below is an example query, the query plan output, and the remote SQL information for such a case. Of particular note are line#4 (NESTED LOOPS) and line#11 (REMOTE TABLE_0002).
What I want to know is more detail on how this NESTED LOOPS JOIN handles the remote operation. For example, for each row that comes out of line#5 and is thus going into the NESTED LOOPS JOIN operation @line#4, does the database jump across the network to do the remote loopkup? Thus if there are 1 million rows, does that mean 1 million network hops? Does batchsize play a role? For example, if the database batches in groups of 100 then does that mean 10 thousand network hops?
I think each row that comes out of line#5 means a network hop to the remote database. But I do not know for a fact.I have done some abbreviating in the plan in an attempt to make it fit on the page (line#7 TA = TABLE ACCESS).
SELECT A.POLICY ,
F.MIN_MEMBER_ID,
MIN(A.EFF_DATE) EFF_DATE,
A.EXP_DATE ,
G.DESCRIPTION PROGRAM_NAME,
[code]...
Performance Tuning :: How Oracle Optimizer Choose Joins (hash / Merge And Nested Loop Join)
Oct 18, 2012I want to know how the Oracle optimizer choose joins and apply them while executing the query. So that I will insure about optimizer join before writing any query.
View 2 Replies View RelatedPL/SQL :: Nested Loops On Outer Joins
Apr 10, 2013I have a select query that was working with no problems. The results are used to insert data into a temp table.
Recently, it would not complete executing. The explain plan shows a cartesian. But, there could be problems with using nested loops on the outer join.
Interestingly, when I copy production code and rename the temp table and rename the view, it works.
CREATE TABLE "CT"
( "TN" VARCHAR2(30) NOT NULL ENABLE,
"COL_NAME" VARCHAR2(30) NOT NULL ENABLE,
"CDE" VARCHAR2(5) NOT NULL ENABLE,
"CDE_DESC" VARCHAR2(80) NOT NULL ENABLE,
[Code]....
Performance Tuning :: Nested Loops
Sep 14, 201010.2.0.1
I am trying to understand the concept of nested loops.
--------
| 0 | SELECT STATEMENT | | 14 | 364 | 4 (0)| 00
:00:01 |
| 1 | NESTED LOOPS | | 14 | 364 | 4 (0)| 00
:00:01 |
[Code]....
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("A"."DEPTNO"="B"."DEPTNO")
Nested loop by defintion means,for every row returned by the outer query,the inner query is executed that many times.
In the above example,oracle does a full table scan and returned 14 rows.Now for dept table,it does a index unique scan and applies the predicate a.deptno=b.deptno and returns 1 row.
My question is why it is returning only 1 row? That measn for every 14 rows,this one row is fetched 14 times.
SQL & PL/SQL :: What Is Hash Join
Jul 12, 2012what is Hash join?how it is different from inner join?what is the sign used for inner join?(eg: like the (+) sign used for outer join)?
View 1 Replies View RelatedPL/SQL :: How To Use Hash Join
Jan 13, 2013If i have a table T1 and a table T2. Table T1 is having 100 rows and table T2 is having 20 rows. When performing a Hash join ,which table should be used to make the hash table ,the larger one or the smaller one and why ?IF the data set is too small for considerations then please conser table T1 with 10 million of rows and table T2 with 1 million of rows.
View 11 Replies View RelatedSQL & PL/SQL :: What Is Hash Join And Sort Merge
Jun 12, 2012I tried to search on google for "Hash Join" And "Sort Merge". But unfortunatly i am unable to understand that articles. "Hash join" And "Sort Merge".
View 3 Replies View RelatedPerformance Tuning :: Cost Calculation For Nested Loop Join
Mar 27, 2012Following is the query on TPC-H schema.
explain plan for select
count(*)
from
orders,
lineitem
where
o_orderkey= l_orderkey.
The trace 10053 (as shown below) for this query shows nested loop join with Lineitem as outer table and Orders as inner table. It is effectively join on composite index (pk_lineitem) of Lineitem and unique index(Pk_orderkey) of Orders table. The cost calculation formula as given in the book as "outer table cost + cardinality of outer table * inner table cost " fails here. I am not able to understand this.
BASE STATISTICAL INFORMATION
***********************
Table Stats::
Table: LINEITEM Alias: LINEITEM
#Rows: 6001215 #Blks: 109048 AvgRowLen: 124.00
Column (#1): L_ORDERKEY(NUMBER)
AvgLen: 6.00 NDV: 1500000 Nulls: 0 Density: 6.6667e-07 Min: 1 Max: 6000000
[code]....
how the cost has been calculated. This does not follow the traditional nested loop cost formula as mentioned in the book.
SQL & PL/SQL :: Transform NOT EXIST Subquery In LEFT OUTER JOIN With Nested Tables?
Mar 22, 2012these are the sample data :
CREATE OR REPLACE TYPE CourseList AS TABLE OF VARCHAR2(64);
CREATE TABLE department (
courses CourseList)
NESTED TABLE courses STORE AS courses_tab;
INSERT INTO department (courses)VALUES (CourseList('1','2','3'));
[code]....
The query returns the correct data, CourseList that are not subset of any other CourseList of the table.
I am trying to convert this not exists in a left outer join query to check if the performance is better, but I don't know how to do it.
I was making some variations of this code :
select d1.courses c_1, d2.courses c_2
from department d1,department d2
where d1.courses<>d2.courses(+);
but it is now working.
How To Do Multiple Loops Through A Cursor
Nov 21, 2011I have a table where each record has a numerical x-coordinate value as one of its fields. I want to loop through a group of the records that have another field in common in a given order. In a nested loop, I would like to subtract the coordinate of the outer loop from the coordinate of the inner loop for all records in the inner loop that appear later in the sequence. The result is a list of the distances between all coordinates.
Example:
x-coordinate
3
4
6
7
It would look like this:
4-3, 6-3, 7-3,
6-4, 7-4,
7-6
I can do this using two nested cursors that select the same thing basically. But the table being selected from is pretty large and it takes forever to keep selecting from the huge table when the inner cursor could just copy the results of the other cursor and repeatedly iterate through them.
Is it possible to copy a cursor's results into another cursor or reset the cursor index back to the beginning so that it doesn't have to do the select statement every time?
SQL & PL/SQL :: How To Use Cursors / Loops And Proper Syntax
May 31, 2011homework assignment using pl/sql based on 2 tables I have created below? I am not sure of how to use cursors, loops and proper syntax.
ASSIGNMENT:
1. Create a PL/SQL Procedure (cursor to loop through the records, check the LastName, then update the grade table
where id=id on grade table)
Rule:
A
‐ LastName ends with a character between A‐F
B
‐ LastName ends with a character between G‐K
C
‐ LastName ends with a character between L‐P
D
‐ LastName ends with a character between Q‐T
E
‐ LastName ends with a character between U‐Z
Create TABLE Registration (RegistrationID number(10), SectionID number(10), CourseID number(10),
SectionNumber varchar2(10),
StudentID number(10), FirstName varchar2(20),
LastName varchar2(20), CourseNumber varchar2(20), CourseName varchar(20));
[code].....
SQL & PL/SQL :: Handling No Of Rows Selected In Loops?
Feb 25, 2012I'm attempting to write a plsql for finding missing archived logs for streams.
requirement is to run a select statement and print
1. 'NOT FOUND' if name column is null
2. '<name of the files>' if rows are returned
3. 'NOT FOUND' if no rows are selected. (here is were i'm having trouble)
code i developed so for:
for cr in (select decode(name, NULL, 'NOT FOUND', name) from v$archived_log where deleted='YES'
and status!='A')
loop
if (cr.name = 'NOT FOUND')
[code]...
PL/SQL :: Use Loops To Retrieve Name Of Emp Table Of Scott Schema
Jan 12, 2013i am trying to use loops to retrieve the ename of emp table of scott schema , then under they are retrieved , all "sal" values appear under them , i do not want employee's salary under each employee , i need retrieve the 14 record of enames , then under them the 14 record of sal column appears , so i used this code :
declare
cursor emp_cur is
select ename from emp;
emp_rec emp_cur%rowtype ;
[code]....
SQL & PL/SQL :: Loops - Find All IDs Who Take Tests Within Rolling Window Of 45 Days?
Mar 10, 2012Main Aim : To find all those id's who have taken all the tests within a rolling window of 45 days.
I have a table "MBS_FIRST_DATE" with the following data :This table has the patients who have the test along with the first date..This table is derived such that it has only one record with the first date of the test irrespective of the test.
create table MBS_FIRST_DATE
(
medical_record_number VARCHAR2(600),
requested_test_name VARCHAR2(39),
result_date DATE
[code]..
Process :will be explaining with a patient id :
1) Consider the patient 1001274 from mbs_first_date table.
2) This patient has an date of July 08th 2008 & test SBP from first table. (keep this test an an anchor).
3) For the patient above loop through the all_recs table with test & result date ordered for the patient. (excluding SBP)
4) The first record we have is CHL with 08/05/2009 (May 8th 2009)..
5) Since this record is not within 45 days from SBP date for the patient..we go to the next record of SBP for the patient.
6) The next record for SBP is 11/05/2009 (May 11th 2009) .
7) Consider the CHL date again which is with 08/05/2009 (May 8th 2009)..
Since both are within 45 days ..store both the values keeping SBP date as an anchor date as it's the test that's having minimum date from table 1. Even though there is one more CHL date which is within 45 days from SBP we don't care about it.
9) Go to the next test for the same patient which is DBP..
10) The DBP first date is July 08th 2008..
11) Since it's not within 45 days from previously stored SBP date (11/05/2009) ignore the record.
12) GO to the next record which is 10/05/2009..as this is within 45 days from SBP & already CHL (stored date) is within 45 days..Grab all the 3 dates as all are within 45 days from anchor date (SBP date).
SO the o/p will be
1001274 SBP 11/05/2009
1001274 CHL 08/05/2009
1001274 DBP 10/05/2009
Code which I wrote :I know some where I am missing the loop
declare
V_ID1 VARCHAR2(200) := '';
V_TEST1 VARCHAR2(200) := '';
V_DATE1 DATE := NULL;
[code]...
Hash Value Generation
Aug 21, 2012I have a question.
When and Where HASH VALUE for a given SQL statement get generated?
SQL & PL/SQL :: How Hash Is Computed
May 22, 2013Is it true that the SQL hash is computed on the SQL text only ?
View 4 Replies View RelatedPerformance Tuning :: Different SQL ID For Same HASH-VALUE?
Nov 2, 2012I see one of my SQL's which is ran by the user on a 10.2.0.3 database changing its SQL_ID after some runs even if the query is not changed a bit! However the HASH VALUE for this query remains the same.
how a same query can have different SQL_ID's but same HASH_VALUE?
Note: Statistics are not modified on the base tables of this query.
SQL & PL/SQL :: Hash Partition Table
Jun 27, 2010I am facing a problem in fetching / updating records from a customer details table having around 20 million records. The table contains around 30 fields with 'MOBILE_NO' as primary key. most of the queries are having 'mobile_no' in where clause .I am planning to hash partition that table using mobile_no column as there is no other column available which can be used for partition.
clarify whether creating hash partition on such key would increase performance of data extraction as I have read on net that hash partitioning is not effective for performance tuning.
Hash Group By Improvement?
Aug 7, 2013I see that one of my queries from an application time is spending most of its time in the hash group by. I'm running Oracle 11g with a quarter rack exadata appliance. Is there a better way to run or design this table? query:
SELECT COUNT(*)
FROM (
SELECT "DDTMDAY", "MRKTNM", "BSMNM", "BSCNM", "CLNM", "CSCDNM", "BTSID", "SECTSEQID", "BNDID", "FAID", SUM("VATTCNT"), SUM("VMBLORGCNT"), SUM("VMBLTERCNT"), SUM("VSILENTRETRYCNT"), SUM("VCUSTBLKCNT"), SUM("VAXSFCNT"), SUM("VCEBLKCNT"), SUM("VWCDBLKCNT"), SUM("VT1BHLBLKCNT"), SUM("VPWRBLKCNT"), SUM("VNONBTSEQBLKCNT"), SUM("VSFULCALLCNT"), SUM("VDRPCALLCNT"),
[code]...
SQL & PL/SQL :: Normal Join And Outer Join
Oct 19, 2013Lets say I have three tables t1 and t2 and t3.
SELECT * FROM T1;
Id
____
1
2
3
4
SELECT * FROM T2;
Id
____
1
SELECT * FROM T3;
Id
____
1
Now when data exists in T2 and T3, I want to return only the records in T1 that match the records in T2 and T3 which is basically a normal join
select t1.id from t1, t2,t3 where t1.id = t2.id and t1.id = t3.id
However when there are no records in T2 or T3, I want to return all records in T1 i.e 1,2,3,4
One way of doing that is using the not exists clause
select * from t1 where not exists ( select null from t2 where t2.Id != t1.id) and not exists ( select null from t3 where t1.Id != t3.id)
Is there a better way of doing this in sql ?
Combining Hash Cluster And Indexes
Oct 28, 2010A basic select and group by query I am optimising for my Database course has returned results that indicate it will perform better on a clustered index when returning a smaller number of rows (5% of the largest table) and on a hash clustered index when returning higher volumes (50% and 80%). I understand that it is possible to use more than one index type on a table to improve performance, but I am struggling to understand how I might establish a hash cluster and a cluster on the same table? and then use hints to drive the query down one access path or the other.
Site admin - this site is a very useful resource.
Single Table Hash Clusters
Mar 16, 2013I created a single table hash cluster like this :
create tablespace mssm datafile 'c:appmssm01.dbf' size 100m
segment space management manual;
create cluster hash_cluster_4k
( id number(2) )
size 8192 single table hash is id hashkeys 4 tablespace mssm;
-- Created a table in cluster with row size such that only one record fits one block and inserted 5 records each with a distinct key value
CREATE TABLE hash_cluster_tab_8k
( id number(2) ,
txt1 char(2000),
txt2 char(2000),
txt3 char(2000)
)
CLUSTER hash_cluster_8k( id );
[code]....
If I issue the same query after creating unique index on hash_cluster_tab(id), the execution plan shows hash access and single I/O (cr = 1).Does it mean that to have single I/o in a single table hash cluster, we have to create unique index? Won't it create additional overhead of maintaining an index?
What is the second I/O needed for in case unique index is absent?
Hash Partition On Primary Key Columns?
Jul 18, 2012I have a existing non partition table with more than 100 million records,planning to re design using Hash partition.This table doesn't has any range column to do range partitioning.
Table has 40 columns with a Primary Key on two columns (guest_sales_Id ,Version Flag). guest_sales_Id is unique for entire table but with anopther column version Flag declared as Primary key.(Version Falg will have only two distinct values in entire table)
If i do hash partition,do i need to declare on two columns which are declared ad Primary key ?If i use only guest_sales_id to declare hash prtition any issues ?
SQL & PL/SQL :: Hash Partition On Fact Table
Sep 27, 2010I created the 32 hash partition on a fact table. Based on hash parititon technique it should evenly distribute data accross the different partition.But when i analyze the table and check the distribution its not at all even.
P_Name Tabspace num_Rows
SYS_P21TBS_TBS0
SYS_P22TBS_TBS0
SYS_P23TBS_TBS0
[Code]....
Security :: How To Decrypt DBMS_CRYPTO.HASH Encrypted Value
Mar 27, 2013note we need to decrypt the data which is encrypted using dbms_crypto.hash algorithm. it is possible to decrypt dbms_crypt.hash
eg
SQL> select DBMS_CRYPTO.hash(utl_raw.cast_to_raw('Foo'), 3) FROM dual;
DBMS_CRYPTO.HASH(UTL_RAW.CAST_TO_RAW('FOO'),3)
--------------------------------------------------------------------------------
201A6B3053CC1422D2C3670B62616221D2290929
Performance Tuning :: Find SQL Using Hash Value - ORA-00060
Nov 18, 2010Getting an ORA-00060 in our database. This is the alert log:
Wed Nov 10 08:01:54 2010
Global Enqueue Services Deadlock detected. More info in file
/opt/oracle/admin/ngboot/bdump/ngboot1_lmd0_13119.trc.
This is part of the lmd file:
oprocp : (nil)
opid : 0
group lock owner : (nil)
xid : 0000-0000-00000000
dd_time : 0.0 secs
dd_count : 0
timeout : 0.0 secs
[Code] ......
How do I find the SQL causing this? I have the hash value of 3180952482. should I open up en SR as this i logged in an lmd trace?
SQL & PL/SQL :: DBMS_CRYPTO Hash A BLOB In A Union Over Dblink?
Dec 27, 2012With this table in local and remote database via a DBLink
CREATE TABLE PICTURES (
ID NUMBER(12),
PICNAME VARCHAR2(20),
PICTURE BLOB
);
How come I can get the hash of the picture column fine like this:
SELECT dbms_crypto.hash@dbLink(PICTURE, 3)from SCHEMA1.PICTURES@dbLink;
but I can't do it in a union with the local database?
SELECT dbms_crypto.hash@dbLink(PICTURE, 3)from SCHEMA1.PICTURES@dbLink
UNION
SELECT dbms_crypto.hash(PICTURE, 3)FROM SCHEMA1.PICTURES;
gives "ORA-06553: PLS-564: lob arguments are not permitted in calls to remote server"
Server Administration :: How To Calculate Number Of Hash Keys
Mar 31, 2011I was reading the documentation for oracle 11gr2, with reference to URL>.....
The following examples show how to correctly choose the cluster key and set the HASH IS, SIZE, and HASHKEYS parameters. For all examples, assume that the data block size is 2K and that on average, 1950 bytes of each block is available data space (block size minus overhead).Note that 34 hash keys are assigned for each data block
how they arrive at 34 hash keys because another portion of the document states
This space determines the maximum number of cluster or hash values stored in a data block. If SIZE is not a divisor of the data block size, then Oracle Database uses the next largest divisor.
if that is the case, then number of hash keys should be 1900/55 = 34.55 which should have rounded up to 35.
Use Range-hash Partitioning Of A Large Dimension Table
Apr 12, 2013At moment we use range-hash partitioning of a large dimension table (dimension model warehouse) table with 2 levels - range partitioned on columns only available at bottom level of hierarchy - date and issue_id.
Result is a partition with null value - assume would get a null partition in large fact table if was partitioned with reference to the large dimension.Large fact table similarly partitioned date range-hash local bitmap indexes
Suggested to use would get automatic partition-wise joins if used reference partitioningWould have thought would get that with range-hash on both dimension.
