7/17/2019 VSAM Presentacin (en ingls)
1/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed.
7/17/2019 VSAM Presentacin (en ingls)
2/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age
%&I'
Foundation Con(epts
VSAM )ata Set 'ypes
VSAM 'erminology
A((ess Method Ser#i(es
'opi(s*
VSAM Con(epts and 'erms
7/17/2019 VSAM Presentacin (en ingls)
3/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age +
What is an access method?
Most (omputer appli(ations are designed to
manipulate data and generate results
ased on the data. )ata must e stored
in a -ay that its retrie#al is easy and
ui(.
A((ess methods are -ays to ma0imi1e the
effi(ien(y of data storage and retrie#al.
Access Methods
An a((ess method a(ts as an interfa(e
et-een a pro(essing program and the
operating system. Continued2
Unit:VSAM Concepts and Terms
Con(epts
Access Methods
DASD
Topic:Foundation Concepts
7/17/2019 VSAM Presentacin (en ingls)
4/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age "
Virtual Storage Access Method
Virtual Storage A((ess Method 3VSAM4 is the
first a((ess method spe(ifi(ally designed to
operate in a #irtual storage en#ironment.
VSAM is more (ompatile -ith operating
systems MVS, MVS/5A and MVS/ESA than
other a((ess methods.
'he (ompatiility of VSAM -ith #arious
operating systems pro#ides greater effi(ien(y
for the appli(ation programs using VSAM and
also for the o#erall en#ironment.
Continued2
Unit:VSAM Concepts and Terms
Con(epts
VSAM
DASD
Topic:Foundation Concepts
7/17/2019 VSAM Presentacin (en ingls)
5/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age 6
VSAM retrieves a record by following these
steps:
7.VSAM interprets the pro(essing program8s
logi(al reuest and determines -hat
ser#i(es are desired.
.VSAM maes the reuired Input or 9utput
3I/94 reuest3s4 to the operating system.
+.'he operating system performs the
physi(al I/9 operation3s4 et-een thede#i(e and the storage.
".VSAM lo(ates and e0tra(ts the desired
data efore returning it to the pro(essing
program.
Virtual Storage Access Method (contd!
Continued2
Unit:VSAM Concepts and Terms
Con(epts
"perating System
DASD
VSAM
#rocessing #rogram
Topic:Foundation Concepts
7/17/2019 VSAM Presentacin (en ingls)
6/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age :
'-o important #ariations in the pro(ess of retrie#ing a re(ord are*
A re(ord reuested y a pro(essing program may already e in #irtual
storage. &o physi(al I/9 operations are needed in su(h a (ase.
Sometimes due to the -ay VSAM stores data and #ariety of pro(essing
options it supports, it must issue se#eral I/9 reuests to retrie#e a single
re(ord.
Virtual Storage Access Method (contd!
Continued2
Unit:VSAM Concepts and Terms
Con(epts
Topic:Foundation Concepts
7/17/2019 VSAM Presentacin (en ingls)
7/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age ;
VSAM groups indi#idual data re(ords into
larger units in order to redu(e the
numer of I/9 reuests reuired -hen
seuentially retrie#ing re(ords.
'hese larger units are transferred et-eenthe )ire(t A((ess Storage )e#i(e
3)AS)4 and #irtual storage y the
operating system.
Virtual Storage Access Method (contd!
Continued2
Unit:VSAM Concepts and Terms
Con(epts
record record record
recordrecord record
DASD
Topic:Foundation Concepts
7/17/2019 VSAM Presentacin (en ingls)
8/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age igh =e#el =anguages, the language (ompilers (on#ert I/9 statements into
(alls to the appropriate VSAM routines. ?hen the I/9 reuest has een
pro(essed, (ontrol is returned to the pro(essing program.
Virtual Storage Access Method (contd!
Unit:VSAM Concepts and Terms
Con(epts
Topic:Foundation Concepts
7/17/2019 VSAM Presentacin (en ingls)
9/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age @
VSAM supports the follo-ing data set types*
EntrySeuen(ed )ata Set 3ES)S4
eySeuen(ed )ata Set 3S)S4
elati#e e(ord )ata Set 3)S4
=inear )ata Set 3=)S4
"verview of Data Set $ypes
Unit:VSAM Concepts and Terms
Con(epts
Topic:VSAM Data Set Types
7/17/2019 VSAM Presentacin (en ingls)
10/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age 7!
e(ords in an ES)S are stored in the order in -hi(h they are -ritten and are
retrie#ed y addressed a((ess. e(ords are loaded irrespe(ti#e of their (ontents
and their yte addresses (annot e (hanged.
ES)S is also referred to as a seuential VSAM data set. 'his is e(ause re(ords in
an ES)S are normally pro(essed seuentially.
ES)S is est suited for appli(ations -here most pro(essing is done seuentially.
%ntry&Se'uenced Data Set
Unit:VSAM Concepts and Terms
Con(epts
Topic:VSAM Data Set Types
7/17/2019 VSAM Presentacin (en ingls)
11/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age 77
e(ords in a S)S are stored in ey seuen(e and are (ontrolled y an inde0. 'he
ey field of re(ords determine the order in -hi(h re(ords are stored.
In a S)S, re(ords (an e pro(essed oth seuentially and randomly using their
ey field #alues.
'he ad#antages of S)S are*
Seuential pro(essing is useful for retrie#ing re(ords in the sorted form
andom or dire(t pro(essing of re(ords is useful in online appli(ations
ey&Se'uenced Data Set
Unit:VSAM Concepts and Terms
Con(epts
Topic:VSAM Data Set Types
7/17/2019 VSAM Presentacin (en ingls)
12/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age 7
)elative )ecord Data Set
e(ords in an )S are loaded into fi0edlength or
#ariale length slots. 'hese re(ords are represented
y the elati#e e(ord &umers 3&s4 of their
slots.
A pro(essing program uses & to pro#ide randoma((ess to re(ords.
'he re(ords in an )S (an also e a((essed
seuentially in its & order. It is also possile to
(on#ert ey #alues into &s.
A((essing data using &s is preferred y many
appli(ations, su(h as in#entory file management.
Continued2
Unit:VSAM Concepts and Terms
Con(epts
)* )+ ),
Slots
7 + "
elati#e e(ord &umers
Topic:VSAM Data Set Types
7/17/2019 VSAM Presentacin (en ingls)
13/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age 7+
-inear Data Set
=)S is a data set (ontaining only a (ontiguous string of data ytes -ith no inter#ening (ontrolinformation.
An =)S is di#ided into lo(s. 'hese lo(s (an e seuentially retrie#ed y a pro(essingprogram in physi(al order. A pro(essing program (an group se#eral logi(al re(ords togetherinto a single lo(
=)S (an e ept permanently in store for enhan(ed performan(e.
'he purpose of the =)S data set type is to pro#ide a format that (an e used more easily -iththe e0tended addressing feature found in Multiple Virtual Storage / Enterprise SystemsAr(hite(ture 3MVS/ESA4.
It is used for spe(ial appli(ations reuiring large amount of data to e maintained in #irtualstorage.
Appli(ation programs prefer an ES)S to an =)S. ES)S pro#ides same pro(essing ailities and(an lo( and unlo( logi(al re(ords automati(ally.
Continued2
Unit:VSAM Concepts and Terms
Con(epts
Topic:VSAM Data Set Types
7/17/2019 VSAM Presentacin (en ingls)
14/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age 7"
A (luster is the (olle(tion of physi(al
data sets that mae up one logi(al
data set.
'he (on(ept of a (luster is more suited
for a S)S.
A S)S (luster has t-o data sets.
9ne data set holds the a(tual data
re(ords. 'he other data set
(ontains an inde0 (omponent.
'he inde0 (omponent permits the
dire(t retrie#al of data.
What is a .luster?
Continued2
Unit:VSAM Concepts and Terms
Con(epts
S)S.C=%S'E
S)S.I&)E5
S)S.)A'A
Topic:VSAM Terminology
7/17/2019 VSAM Presentacin (en ingls)
15/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age 76
What is a control interval?
A (ontrol inter#al is the amount of data transferred et-een the de#i(e and #irtual
storage.
?hen a re(ord is read from or -ritten to a data set, VSAM groups indi#idual data
re(ords into larger units of storage. 'hese units of storage are (alled (ontrol
inter#als.
.ontrol /nterval
Continued2
Unit:VSAM Concepts and Terms
Con(epts
Topic:VSAM Terminology
7/17/2019 VSAM Presentacin (en ingls)
16/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age 7:
A (ontrol inter#al is the amount of data
transferred et-een the de#i(e and
#irtual storage.
VSAM groups indi#idual data re(ords
into larger units of storage. 'heseunits of storage are (alled (ontrol
inter#als.
All (ontrol inter#als for a gi#en data set
are of the same si1e. >o-e#er, the
re(ords -ithin a (ontrol inter#al
(an #ary in length.
.ontrol /nterval (contd!
Unit:VSAM Concepts and Terms
Con(epts
)* )* )*0nused
Space
1
+
2
,
1
2
+
+
2
3 *
4 2
2 5
5
A 3!"< ytes4
Control Inter#al
Topic:VSAM Terminology
7/17/2019 VSAM Presentacin (en ingls)
17/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age 7;
'he (ontrol inter#als for a data set are
grouped Into one or more (ontrol
areas.
'he numer of (ontrol inter#als in a
(ontrol area is fi0ed y VSAM.
.ontrol Area
Unit:VSAM Concepts and Terms
Con(epts
25 24 23 *2
*+ *1 *5 +2
+*
+3
++
,2
+1 +5
,5 ,6
Control Area
-ith Control Inter#als
Topic:VSAM Terminology
7/17/2019 VSAM Presentacin (en ingls)
18/39
MVS/ESA Fundamentals of VSAM
Copyright IBM Corp., !!!, !!". All rights reser#ed. $age 7ori1.
$ntr.
67
:@
FEE
+"6
+":
+;;
FEE
+@"
"!!
"7!
""@
":@
6!!
6!
6@
Top Related