Db2 Training Class 004

7/24/2019 Db2 Training Class 004

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www.mainframes-online-training.weebly.com Polsani Anil Kumar

COBOL-DB2 Program

DB2 Training Class 04
http://www.mainframes-online-training.weebly.com/http://www.mainframes-online-training.weebly.com/http://www.mainframes-online-training.weebly.com/


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Required Steps

Write a COBOL + DB2 rogramComile t!e COBOL + DB2 rogram

"#ecute t!e rogram.


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Required Copyboos

SQLCAcoy boo$

Hostvariable/DCLGENcoyboo$

Alication rogram containing %&L statement s!oul' !a(e %&LCA

coyboo$. %&LCA coyboo$ is a collection of (ariables t!at areu'ate' for e(ery %&L statement.

)!is coyboo$ is of 136bytes in lengt!.

Contains most imortant (ariable li$e %&LCOD"* %&L"D

SQLCODEcontain t!e status co'e after e(ery "#ecution of %&L

statement w!ose icture clause is S9(9,COMP-3.

SQLERRDis an occurs 'ata item in w!ic! t!e occurrence contains

t!e number of effecte' rows by a gi(en uery i.e. SQLERRD(3,.


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!ost "ariable

)!ese are (ariable 'efine' in t!e ostla!"#a"eto use in

alication rogram.

/ost 0ariable are t!e only means of mo(ing 'ata from an'

to DB2 tables

We use DCLGEN tool to ro'uce !ost (ariable are t!e

same as t!e column of t!e tables

We nee' to co'e !ost (ariables wit! in t!e %&L statement

but s!oul' be rece'e' by $olo!(%&'


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#mbedded S$L

All t!e %&L relate' statement s!oul' be co'e'1embe''e' in

between

""C%&L 3 "4D-""C.

Bot! %&LCA an' !ost (ariable s!oul' be co'e' in between

""C %&L an' "4D-""C wit! 54CL6D" %tatement.

""C%&L ""C%&L

54CL6D" %&LCA 54CL6D" DCL7"4

"4D-""C. "4D-""C.


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#mbedded S$L Statement

""C%&L 54%") 54)O "8P9)AB:"4O*"4A8",

0AL6"%:;/%-"4O*;/%-"4A8",

"4D-""C.

""C%&L %"L"C) "4O*"4A8" 54)O ;/%-"4O*;/%-"4A8">?

"4D-""C.

""C%&L 6PDA)" "8P9)AB %") "4A8"=;/%-"4A8"

"4D-""C.

""C%&L D"L")"


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Program Preparation

We nee' to follow few stes

Precomile

Comile3 lin$

Bin'

Pac$age:B54DPACKA7",

Plan:B54DPLA4,


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Pre%ompile

%earc!esall t!e %&L statements an' inclu'e members an'

comments out e(ery %&L statements in t!e rogram

)!e %&L statement are relace'by a callstatement along

wit! t!e arameters

All %&L statements are e#tracte'an' ut in a DB8

Bot! %&LCA 3 DCL7"4 coyboo$s are e#an'e' in t!e

re comile rocess only.

5t also assign a time stam to t!e mo'ifie' co'e an' DB8

member.


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Compile and Lin

8o'ifie' COBOL co'e outut is t!en comile'

Comile' co'e is t!en lin$ e'ite' to an "#ecutable

loa' mo'ule


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B&'D Pro%ess

A tye of comiler for %&L statement using a re written

rogram i.e. 5K@"?

5t rea's t!e %&L statement from t!e DB8 an' ro'uces a

mec!anism to access 'ata as 'irecte' by t!e %&L statement

5n t!is bin' rocess it c!ec$s t!e synta#* c!ec$s for t!e

correctness of t!e table 3 columns 'efinitions against t!e

catalog information an' erform aut!entication (ali'ation

)!e outut of t!e bin' rocess can be a ac$age or a lan


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Pa%age ( its )d"antage

Pac$age is boun' form of %&L statement

Ava!ta"es;

e'uce' bin' time

Can secify bin' oeration in t!e rogrammer le(el

Pro(i'e remote 'ata access


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PL)'

Pac$age is not "#ecutable w!ere as lan is "#ecutable

An alication lan contain one or bot! of t!e following

elements

A list of ac$age names

)!e boun' form of %&L statement ta$en from one or more

DB8

"(ery DB2 alication reuires an alication lan

Plans are create' using t!e DB2 sub comman' B54D PLA4


14/23www.mainframes-online-training.weebly.com Polsani Anil Kumar

Bind Parameters
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Bind Parameters

11%%)%54 DD

D%4 %%)"8:DB7,

B54D PACKA7":


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Bind Parameters

PKL5%); PKL5%) is a bin' arameter of bin' lan. Pac$ages to be

connecte' wit! lan are name' !ere.

AC)5O4:ADDE"PLAC", ac$age or lan is a'' or relace'. 'efault

is "PLAC".

AC&65"A4D "L"A%";

AC&65":6%"1ALLOCA)"loc$s table an' table sace on use

"L"A%":CO885)1D"ALLOCA)", release w!en t!e lan

terminates

%&L"O:4OPACKA7"1CO4)546", it says weat!er to create t!e

ac$age in case of sl error

"PLA54:"%14O, loa's t!e access at! selecte' by t!e otimFerin

lan9table. no is 'efault


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&solation Le"els

Lost *+ates% )!is e(ent occurs w!en two

transactions rea' t!e same 'ata* bot! attemt to

u'ate t!at 'ata* an' one of t!e u'ates is lost.

Dirt, Reas% )!is e(ent occurs w!en a transaction

rea's 'ata t!at !as not yet been committe'.

No!re+eatable Reas% )!is e(ent occurs w!en a

transaction rea's t!e same row of 'ata twice* but gets

'ifferent results eac! time

Pa!tos')!is e(ent occurs w!en a row of 'ata

matc!es some searc! criteria but initially is not seen.


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&solation le"els

Re+eatable ReaRea Stabilit,

C#rsor Stabilit,

*!$oitte Rea


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.e Re+eatable Rea &solation Le"el

)!e eeatable ea' isolation le(el is t!e most restricti(e

isolation le(el a(ailable.

W!en t!is isolation le(el is use'* e(ery row t!at is reference'

in any manner by t!e isolate' transaction is Gloc$e'G for t!e'uration of t!at transaction.

)!us* if a transaction scans ?*>>> rows in or'er to retrie(e ?>*

loc$s are acuire' an' !el' on all ?*>>> rows scanne'Hnot

Iust on t!e ?> rows retrie(e'.


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T*e Read Stability &solation Le"el

w!en t!e ea' %tability isolation le(el is use'* only rows t!atare actually retrie(e' by a single transaction are loc$e' for t!e

'uration of t!at transaction.

!antoms* !owe(er* can an' may be seen.

if a transaction scans ?*>>> rows in or'er to retrie(e ?>* loc$s

are only acuire' an' !el' on t!e ?> rows retrie(e'Hnot on all

?*>>> rows scanne'.

An' because fewer loc$s are acuire'* more transactions canrun concurrently.


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T*e Cursor Stability &solation Le"el

W!en t!e Cursor %tability isolation le(el is use'* only t!e row

t!at is currently being reference' by a cursor is loc$e'. )!e

loc$ acuire' remains in effect until t!e cursor is reositione'

Hmore often t!an not by e#ecuting t!e


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T*e +n%ommitted Read &solationLe"el

)!e uncommitte' rea' isolation le(el is t!e least intrusi(eisolation le(el ro(i'e'.

5n fact* w!en t!e uncommitte' rea' isolation le(el is use'* rows

t!at are retrie(e' by a single transaction are only loc$e' if

anot!er transaction attemts to 'ro or alter t!e table from w!ic!

t!e rows were retrie(e'. Because rows often remain unloc$e'

W!en t!is isolation le(el is use'* 'irty rea's* nonreeatable

rea's* an' !antoms can occur.

)!e uncommitte' rea' isolation le(el is commonly use' for

transactions t!at access rea'-only tables1(iews or transactions

t!at e#ecute ueries on w!ic! uncommitte' 'ata from ot!er

transactions will !a(e no a'(erse affect


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T*an ,ou

Documents

Db2 Training Class 004