Thomas Niewel - Gate..

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Transparent Gateway for DB2 a success story

Thomas NiewelOracle Deutschland GmbH

[email protected]

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Agenda

• The Geomarketing Project

• TG4DB2 – How it works

– Pre-Processing

– Post-Processing

– Gateway Parameters

• Things to think about in a dB2 world

– DB2 Locking Model

– Predicates

– Lessons we have learned

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The project – Geomarketing • The service center of a bank needed to provide a

control instrument for marketing activities

• The marketing actions should be controlled by spatial data and operational data

• The requirements for the platforms were

– Spatial Data should reside Windows

– Operational Data is stored on DB2 for z/OS

• There are existing DB2 for z/OS datawarehouseswhich should be used as source

• There are 3 different LPARs with DB2 data

• RACF should be used to autenticate users

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The project – Geomarketing

DB2

DB2

DB2

TG4DB2NET

TG4DB2

TG4DB2NET

NET

GIS-DB Server

Oracle 8.1.7.4

Integraph

LPAR1

LPAR2

LPAR3

zSeries

WebBrowser

Windows

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• A sample request

– Show me all customers who live in the city of Fürstenfeldbruck which do not have any shares

– The result is a Map of the city Fürstenfeldbruck where you can see the areas of the city combined with the result set of the request

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• Project plan

– Suppliers had to build a prototype

– The customer evaluated the prototypes

• Performance was a key success factor

– Performance also was the main challenge

• DB2 had to be accessed with only little ressource consumtion

• DB2 Utilities should not be interfered

• Sometimes a great number of rows is transferred

• Distributed Queries(Oracle/DB2) had to be used

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The Project – Geomarketing • The way how Transparent Gateway for

DB2(TG4DB2) works had to be understood

• Features which speed up Bulk Transfers with TG4DB2 had to be used

• Efficient queries to access DB2 had to be developed

– That means the DB2 Optimizer had to be known

• The DB2 Locking behaviour had to be understood

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Transparent Gateway for DB2 How it works

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Problem areas

• SQL Dialects

• DB2 Locking Model

• Query Performance

• Transparency

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How does a Gateway work ?

Oracle DB2 for z/OS

Select Max(Salary) from tab1@DB2 Where Name= ‘MAIER‘

Step 1 Step 2

DatatransferStep 3

Step 4

Select Max(Salary) from tab1 Where Name= ‘MAIER‘

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Oracle DB2 for z/OS

Select Name,age from tab1@DB2 Where NVL(Age,18)= 18

Step 1 Step 2

DatatransferStep 3

Step 4

Select Name,age from tab1 Where Value(Age,18)= 18


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Oracle DB2 for z/OS

Select * from tab1@DB2Where Soundex(Column1)= ‘Scott‘

Select * from tab1Step 1 Step 2

Datatransfer

Select * from temptab Where Soundex(Column1)= ‘Scott‘

Step 3

Step 4


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Gateway Performance• Compatible Functionalities

– Good performance

• Translated Functionalities

– Gateway Pre-Processing

– Good Performance

• Compensated Functionalities

– Gateway Post-Processing

• Performance implications

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• Compatible functions

– AVG

– CONCAT

– COUNT (*) only

– COUNT(DISTINCT expression)

– MAX

– MIN

– SUM

– ....

• Translated functions

– NVL – Value

– .....

Gateway Performance

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How can Post-Processing be discovered• Bad response time (SQL Trace)

• Gateway Trace

• Explain Plan

– UTLXPLAN

– UTLXPLS

– PLAN_TABLE

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Postprocessing - sample

explain plan for

select b.ename, b.empno from tniewel.emp@epg1 a, scott.emp@epg1 b where a.empno=b.empno and soundex(a.ename)='MAIER'

/

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Postprocessing - sample

-----------------------------------------------------------------------------------------------

| Id | Operation | Name | Rows | Bytes | Cost | TQ |IN-OUT| PQ Distrib |

-----------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 1 | 40 | 1 | | | |

|* 1 | HASH JOIN | | 1 | 40 | 1 | | | |

|* 2 | FILTER | | | | | | | |

| 3 | REMOTE | | | | |E.,OM |SERIAL| |

| 4 | REMOTE | | 1 | 20 | |E.,OM |SERIAL| |

-----------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

1 - access("A2"."EMPNO"="A1"."EMPNO")

2 - filter(SOUNDEX("A2"."ENAME")='MAIER')

Slave SQL Information (identified by operation id):

---------------------------------------------------

3 - SELECT "EMPNO", "ENAME" FROM "TNIEWEL"."EMP"

4 - SELECT "EMPNO", "ENAME" FROM "SCOTT"."EMP"

Note: cpu costing is off

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Without Postprocessing

explain plan for

select b.ename, b.empno from tniewel.emp@epg1 a, scott.emp@epg1 b where a.empno=b.empno and a.ename='MAIER'

/

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Without Postprocessing

-----------------------------------------------------------------------------------------------


-----------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | | | | | | |


-----------------------------------------------------------------------------------------------


---------------------------------------------------

1 - SELECT A1."ENAME", A1."EMPNO" FROM "TNIEWEL"."EMP" A2, "SCOTT"."EMP" A1 WHERE A2."EMP

NO"=A1."EMPNO" AND A2."ENAME"='MAIER'

Note: rule based optimization

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Distributed Joins – how can „splitted“ Queries be prevented

explain plan for

select a.ename from tniewel.emp a, tniewel.emp@epg1 b, scott.emp@epg1 c where a.ename=b.ename and b.ename=c.ename;

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------------------------------------------------------------------------------------------------


------------------------------------------------------------------------------------------------


|* 1 | HASH JOIN | | 1 | 21 | 3 | | | |

| 2 | MERGE JOIN CARTESIAN| | 1 | 14 | 2 | | | |


| 4 | BUFFER SORT | | 82 | 574 | 2 | | | |

| 5 | TABLE ACCESS FULL | EMP | 82 | 574 | 2 | | | |


------------------------------------------------------------------------------------------------


---------------------------------------------------

1 - access("A"."ENAME"="B"."ENAME" AND "B"."ENAME"="C"."ENAME")


---------------------------------------------------

3 - SELECT "ENAME" FROM "SCOTT"."EMP"

6 - SELECT "ENAME" FROM "TNIEWEL"."EMP"


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explain plan for

select a.ename from tniewel.emp a where a.ename = (select b.ename from tniewel.emp@epg1 b, scott.emp@epg1 c where b.ename=c.ename);


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-----------------------------------------------------------------------------------------------


-----------------------------------------------------------------------------------------------


|* 1 | TABLE ACCESS FULL | EMP | 1 | 7 | 2 | | | |


-----------------------------------------------------------------------------------------------


---------------------------------------------------

1 - filter("A"."ENAME"= (SELECT "A2"."ENAME" FROM "SCOTT"."EMP"@EPG1.DE.ORACLE.COM "A1"))


---------------------------------------------------

2 - SELECT A2."ENAME" FROM "TNIEWEL"."EMP" A2, "SCOTT"."EMP" A1 WHERE A2."ENAME"=A1."ENAM

E"

Note: cpu costing is off

22 Zeilen ausgewõhlt.


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• Create views in DB2 – Be careful with View Materialization

• View Merge vs. View Materialization•View Materialization is performed when a view is complex – e.g. when sorts need to be performed

• Explain of the View

• Use Filters


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Traces - Gateway Trace

• Gateway Parameters

• Tracelevel=4

• Dedicated Trace Gateway makes live easier

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//////////////////////////////////////////////////////////////////////////// Oracle for OS/390 Diagnostic Trace -- 2003/01/15 07:19:07.357 // System MVS08 Subsystem EPO3 Service EPG1 Session 16 PID 00020010////////////////////////////////////////////////////////////////////////////*** hoapars SQL : SELECT "NAME" FROM "SYSIBM"."SYSTABLES"fdsapi:SQL statement follows. Length=39SELECT "NAME" FROM "SYSIBM"."SYSTABLES"*** hoapars SQL : SELECT "EMPNO", "ENAME", "JOB", "MGR", "HIREDATE", "SAL", "COMM", "DEPTNO" FROM "TNIEWEL"."EMP"fdsapi:SQL statement follows. Length=95SELECT "EMPNO", "ENAME", "JOB", "MGR", "HIREDATE", "SAL", "COMM", "DEPTNO" FROM "TNIEWEL"."EMP"

Traces – Gateway Trace

Gateway Trace

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SQL Trace Prerequisite: timed_statistics=true;

user action - Connect

Select sid, serial#, osuser, username from V$session

1. SQL> select sid, serial#, osuser, username from v$session; SID SERIAL# OSUSER USERNAME--------- --------- -------------------------- ----------------------

....7 38 SYSTEM

9 70 TNIEWEL2 exec sys.dbms_system.set_sql_trace_in_session(9, 70,TRUE)

user action – Work with Application

exec sys.dbms_system.set_sql_trace_in_session(9, 70,FALSE)

Format Trace Files with TKPROF

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Gateway Parameters

• HS_RPC_FETCH_SIZE=40000

• DB2_STATS=YES

• IDLE_TIMEOUT

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Important – Gateway Parameters

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Parameter DB2STATS=YES

• DB2 catalog Statistics are used influence the Execution plan

• Table Cardinality• Key Column Cardinality

• What are the results of that setting

• Join Sequence may change

• Small remote-DB2-Tables are completely transferred

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Parameter DB2STATS=YES

• Sample Plan_table output• Sysibm.Systables, Sysibm.Syscolumns (Only Key Columns)

• Column: Cardf• Select * from tniewel.emp@epg1

-----------------------------------------------------------------------------------------------


-----------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 10000 | 566K| | | | |

| 1 | REMOTE | | 10000 | 566K| |E.,OM |SERIAL| |

-----------------------------------------------------------------------------------------------


---------------------------------------------------

1 - SELECT "EMPNO", "ENAME", "JOB", "MGR", "HIREDATE", "SAL", "COMM", "DEPTNO" FROM "TNIE

WEL"."EMP"

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DB2 Locking

IRLM (Internal Ressource Lock Manager)

Row Locks possible - Page Locks were used because of performance reasons

Lock Escalation

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DB2 Locking

DB2 Locking is behaviour is determined by the Isolation Level of the Gateway Plan

CS – Cursor Stability RR – Repeatable ReadRS – Read StabilityUR – Uncommitted Read

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Locked

Read Stability

Locked

Cursor Stability

sharelocks

Locked

Repeatable Read

Locked

UncommittedRead

Nothing Qualifying Row All Rows Row accessed Read

DB2 Locking

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DB2 Locking - Problems

Problem at the customer site:

• The Gateway holds Locks ! Our Batches Abend with SQLCODE –911

Is this really a gateway problem ?

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Duration of Page and Row Locks:

If a page or row is locked, DB2 acquires the lock only whenit is needed. When the lock is released depends on many factors,but it is rarely held beyond the next commit point.

Quelle: DB2 Version 7 Administration Guide

.....Commit Work as Soon as Is Practical: To avoid unnecessary lock contentions, issue a COMMIT statement as soon aspossible after reaching a point of consistency, even in read-only applications. To prevent unsuccessful SQL statements(such as PREPARE) from holding locks, issue a ROLLBACK statement after a failure.

DB2 Locking

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DB2 - SQL – Tuning Hints

• Use Functions on columns in where condition which are also available in DB2

• Predicates in DB2

– Indexable

• Index can be used

– Stage 1

• Predicates, which are not of Type „Stage 1“ are evaluated by the RDS(Relational Data System) which is more expensive

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Predicates – Source DB2 Administration Guide

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Lessons we have learned

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Lessons we have learned • DB2 Locking

• Commit´s – also after Read operations

• If Consistency doesn´t matter• Bind TG4DB2 Plan with Isolation Level

UR (TG4DRDA (DRDA_ISOLATION_LEVEL=NC)

• Hanging Sessions

• Alter Session Close Database Link xxx

• Should be executed when a logical application unit is finished.

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• Try to make bulk transfers „small“

• use as much filters as possible on remote DB • The split of distributed joins (Oracle / DB2) sometimes is more efficient

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• Oracle functions in SQL can produce a lot of overhead

• Sample:

Select a.*,b.* from testtn1@epg1 a, testtn2@epg1 b where

a.c3 between to_char(sysdate-1,'YYYY-MM-DD')||'-00.00.00.000000'

and to_char(sysdate,'YYYY-MM-DD')||'-00.00.00.000000' and

a.c2=b.c2

• The use of Bind variables improves the performance

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More...

• Gateway Passthrough

• Allows input of native DB2 Syntax without Gateway Pre- and Postprocessing

• Call of DB2 Stored Procedures• Allows the use of static SQL• DB2 Stored Procedure result sets are not supported

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PassthroughDECLARE

CRS binary_integer; RET binary_integer; VAL VARCHAR2(10);AGE Number

BEGIN

CRS:=DBMS_HS_PASSTHROUGH.OPEN_CURSOR@gtwlink;

DBMS_HS_PASSTHROUGH.PARSE@gtwlink(CRS,’SELECT NAME, AGE FROM PT_TABLE’);

BEGIN

RET:=0;

WHILE (TRUE)

LOOP

RET:=DBMS_HS_PASSTHROUGH.FETCH_ROW@gtwlink (CRS,FALSE);

DBMS_HS_PASSTHROUGH.GET_VALUES@gtwlink (CRS,1,VAL);

DBMS_HS_PASSTHROUGH.GET_VALUES@gtwlink (CRS,2,AGE);

INSERT INTO PT_TABLE_LOCAL VALUES (VAL);

END LOOP;

EXCEPTION

WHEN NO_DATA_FOUND THEN

BEGIN

DBMS_OUTPUT.PUT_LINE(’END OF FETCH’);

DBMS_HS_PASSTHROUGH.CLOSE_CURSOR@gtwlink(CRS) ;

END;

END;

......

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DB2 Stored Procedures

Can be called from PL/SQL

DECLARE

INPUT VARCHAR2(15);

RESULT NUMBER(8,2);

BEGIN

INPUT := ‘JOHN SMYTHE’;

SYSPROC.REVISE_SALARY@DB2(INPUT, RESULT);

UPDATE EMP SET SAL = RESULT WHERE ENAME = INPUT;

END;

....

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The results...

• Geomarketing is in Production

• The response time is o.k.

• TG4DB2 V9.2 (compared to version 8.1.7) generated improved „distributed query“ execution plans

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Date post:	10-May-2015
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Thomas Niewel - Gate..

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