20031208-Adabas 201 for the Natural Programmer

8/4/2019 20031208-Adabas 201 for the Natural Programmer

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Efficient Adabas Access


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ADABAS Access

READ PHYSICAL

READ BY ISN (GET)

READ LOGICAL

FIND

HISTOGRAM

* Select the correct access method.* Code it efficiently.


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Natural CommandsREAD Physical

Data Storage

Use when reading more than 20% of the records in a file

Generally least expensive method to read all records

Only update if

Potential double updates will not be a problem

Restartability not a problem

Safest to run when file not being updated


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ADABAS Access -READ PHYSICAL

Access to Data Storage only.

Records returned in the order they arestored physically in Data Storage

* Can results in 4 I/Os (1 per block) & 14 ADABAS Calls

* Order of records returned: 2,1,14,3,5,12,4,6,7,8,11,9,20,21


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Natural CommandsREAD by ISN

Data Storage

Use when reading more than 20% and some updating

ISN use ensures no double updates & no missed updates

ISN may be used as restart point

Second fastest access method

Used when updating file but not one for one with the

outside loop

Address

Converter


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ADABAS Access -

READ BY ISN Access to Address Converter & Data Storage

Records returned in ascending ISN order

125 125 126 127 126 127 127 127 128 0

128 126 0 125 0 0 0 0 0 128128


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Natural CommandsREAD Logical

Inverted List

AddressConverter Data Storage

Use when reading 1 record or a small range of

records

Returned in sorted order by index read

Be careful when updating read key fields

1

2

3

4


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ADABAS Access -READ LOGICAL

Returns records in sequence byDescriptor, Sub-, or Super-Descriptor

Accesses Inverted List, AddressConverter, and Data Storage

Useful for reading small portion of a file

Consistent performance


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ADABAS Access - READ LOGICAL

2 1 4 1 2 2 4 1 3 0

0 0 0 0 0 0 0 0 0 0

0

LAST-NAME COUNT

ADAMS 3 2 5 9BAKER 1 4

BROWN 2 1 6

CARLSON 3 3 7 8

ISNS

4 BAKER 8 CARLSON FREE2 ADAMS PADDING

1 BROWN 6 BROWN 5 ADAMS PADDING

9 ADAMS FREE3 CARLSO 7 CARLSON FREE


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Natural CommandsFIND

Inverted List

AddressConverter

Work

Data Storage

Memory

1

or1

2

3

4or4


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Useful for accessing small groups of records with

one or more selection criteria

Returns records in *ISN sequence

A FIND which selects a set of records > 51 will

generate I/O to work part 3

Complex FINDs can generate I/O to work part 2


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Simple find (algorithm 1):

LAST-NAME = BROWN

Moderate complexity (algorithm 2):

LAST-NAME = BROWN OR JONES

Complex FIND (algorithm 4):

FIND PERSONNEL WITH AGE > #AGE

AND SEX = #SEX AND VET-STATUS = V


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ADABAS Access - FIND

Selects a set of records & returns that setin ISN sequence

Access Inverted List & select set of

records which meet search criteria If number of ISNs > 51, ADABAS uses

Work DS

Access Address Converter to obtain DSRABN


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Read block from Data Storage & locaterecord

Repeat for each ISN in the list

FIND SORTED BY - avoid when possible Non descriptor search criteria - ensure it

is not primary criteria


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ADABAS Access - FINDFIND PERSONNEL WITH NAME = ADAMS

125 125 126 127 126 127 127 127 128 0

128 126 0 125 0 0 0 0 0 128

128

Value Count ----------------------ISNs---------------------------------------------------------------------------------- ADAMS 4 2 7 9 12

BAKER 3 1 3 20

CHARLES 3 5 6 8

DAVENPORT 2 11 21

DAVIS 2 4 14


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125 125 126 127 126 127 127 127 128 0

128 126 0 125 0 0 0 0 0 128

128

Value Count ----------------------ISNs----------------------------------------------------------------------------------

ADAMS 4 2 7 9 12

BAKER 3 1 3 20

CHARLES 3 5 6 8

DAVENPORT 2 11 21

DAVIS 2 4 14

Access Inverted

List for value

ADAMS.

Results in ISN listof 2, 7, 9, 12


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125 125 126 127 126 127 127 127 128 0

128 126 0 125 0 0 0 0 0 128

128


BAKER 3 1 3 20

CHARLES 3 5 6 8

DAVENPORT 2 11 21

DAVIS 2 4 14

Access Address

Converter to

obtain RABN.


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125 125 126 127 126 127 127 127 128 0

128 126 0 125 0 0 0 0 0 128

128


BAKER 3 1 3 20

CHARLES 3 5 6 8

DAVENPORT 2 11 21

DAVIS 2 4 14

Access Data

Storage to

retrieve record.


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Access Inverted List for ADAMS, BAKER,

CHARLES, DAVENPORT, and DAVIS

Form ISN list:1,2,3,4,5,6,7,8,9,11,12,14,20,21. Thismerging is additional work not required by

READ LOGICAL. Access Address Converter and Data Storage.

Records NOT returned in name order!

FIND IN PERSONNEL WITH LAST-NAME = ADAMSTHRU DAVIS


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ADABAS Access - FIND Should only be used if no work file I/O is

involved (


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Natural Commands

HISTOGRAM

Inverted List

Use when only descriptor, sub-descriptor or super

descriptor components needed

Use for validation of data


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ADABAS Access -HISTOGRAM

Only has Access to the Inverted Lists.

Returns two items:

Value of descriptor

Number of records which have that value

ISNs are NOT returned to Natural eventhough theyre in the inverted lists.

Sex

Value Count -----------ISNs------------------------------------------------------------------------------------------------------------------

F 234 2 3 7 9 10 11 15 16 17 21 25

M 293 1 4 5 6 8 12 13 14 18 19 20

1. Returns valueof F and

*NUMBER = 234


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ADABAS Access -HISTOGRAM

Beginning and Ending Values UsuallySpecified.

Efficient way to determine if a particular value

exists for a descriptor. Efficient way to determine how many records

have a particular value for a descriptor.

If all data for requirements is available inInverted List - Use HISTOGRAM or FINDNUMBER


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Direct Calls

How records are accessed by ADABASDirect Call Action Performed

L1 READ by ISN

L2 READ physical

L3 READ logical

L9 HISTOGRAM


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Direct Calls


L4 READ by ISN w/ hold

L5 READ physical w/ hold

L6 READ logical w/ hold


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Direct Calls


S1 FIND

S4 FIND w/ hold

A1/A4 UPDATE

N1/N4 STORE

E1/E4 DELETE


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ADABAS Access - SUMMARY

GET - Reread Record HISTOGRAM - All required data available in

Inverted List

READ PHYSICAL - More than 20% of file and no

updates

READ BY ISN - More than 20% of file and updates

FIND - Multiple, non-contiguous values ofdescriptor; Small set of records; sequence notimportant

READ LOGICAL - Most others


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Natural 4 and Adabas Dynamic change of reading direction within an active

READ or HISTOGRAM processing loop.

Dynamic repositioning within a READ processingloop.

New comparators LESS/GREATER THAN and

LESS/GREATER EQUAL for READ andHISTOGRAM statements.

Support of Multi-Fetch in FIND, HISTOGRAM andREAD statements.

New keyword TO that enables end of range condition(ENDING AT) to be controlled by the database itself.

Support of the Adabas Transaction Manager.


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Questions

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20031208-Adabas 201 for the Natural Programmer

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