Efficient Adabas Access 2 ADABAS Access READ PHYSICAL READ BY ISN (GET) READ LOGICAL FIND HISTOGRAM...

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 are

stored physically in Data Storage

* Can results in 4 I/Os (1 per block) & 14 ADABAS Calls* 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* 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 0128 126 0 125 0 0 0 0 0 128128 …

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Natural CommandsREAD Logical

Inverted List

Address Converter 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

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2

3

4

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ADABAS Access -READ LOGICAL

• Returns records in sequence by Descriptor, Sub-, or Super-Descriptor

• Accesses Inverted List, Address Converter, 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 00 0 0 0 0 0 0 0 0 00 …

LAST-NAME COUNTADAMS 3 2 5 9BAKER 1 4BROWN 2 1 6CARLSON 3 3 7 8

ISNS

4 BAKER 8 CARLSON FREE2 ADAMS PADDING1 BROWN 6 BROWN 5 ADAMS PADDING9 ADAMS FREE3 CARLSON 7 CARLSON FREE

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Natural CommandsFIND

Inverted List

Address Converter

Work

Data Storage

Memory1 or 1

2

3

4 or 4

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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 set

in 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 DS RABN

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ADABAS Access - FIND• Read block from Data Storage & locate

record

• 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’FIND PERSONNEL WITH NAME = ‘ADAMS’

125 125 126 127 126 127 127 127 128 0128 126 0 125 0 0 0 0 0 128128 …

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 0128 126 0 125 0 0 0 0 0 128128 …


BAKER 3 1 3 20

CHARLES 3 5 6 8

DAVENPORT 2 11 21

DAVIS 2 4 14

Access Inverted Access Inverted List for value List for value ADAMS.ADAMS.

Results in ISN Results in ISN list of 2, 7, 9, 12list of 2, 7, 9, 12

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125 125 126 127 126 127 127 127 128 0128 126 0 125 0 0 0 0 0 128128 …


BAKER 3 1 3 20

CHARLES 3 5 6 8

DAVENPORT 2 11 21

DAVIS 2 4 14

Access Address Access Address Converter to Converter to obtain RABN.obtain RABN.

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125 125 126 127 126 127 127 127 128 0128 126 0 125 0 0 0 0 0 128128 …


BAKER 3 1 3 20

CHARLES 3 5 6 8

DAVENPORT 2 11 21

DAVIS 2 4 14

Access Data Access Data Storage to Storage to retrieve record.retrieve record.

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ADABAS Access - FIND

• 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. This merging 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 = ‘ADAMS’ FIND IN PERSONNEL WITH LAST-NAME = ‘ADAMS’ THRU ‘DAVIS’THRU ‘DAVIS’

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ADABAS Access - FIND

• Should only be used if no work file I/O is involved (<51 records).

• Useful for multiple, non-contiguous values of descriptor (NAME = ‘SMITH’ OR = ‘CARROLL’ OR = ‘JONES’).

• Trade offs between READ logical and FIND.

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Natural CommandsHISTOGRAM

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 even though they’re 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 value 1. Returns value of ‘F’ and of ‘F’ and *NUMBER = 234*NUMBER = 234

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ADABAS Access - HISTOGRAM

• Beginning and Ending Values Usually Specified.

• 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 in Inverted List - Use HISTOGRAM or FIND NUMBER

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Direct CallsHow records are accessed by ADABAS

Direct Call Action Performed

L1 READ by ISN

L2 READ physical

L3 READ logical

L9 HISTOGRAM

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L4 READ by ISN w/ hold

L5 READ physical w/ hold

L6 READ logical w/ hold

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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 of descriptor; Small set of records; sequence not important

• 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 processing

loop.• New comparators LESS/GREATER THAN and

LESS/GREATER EQUAL for READ and HISTOGRAM statements.

• Support of Multi-Fetch in FIND, HISTOGRAM and READ 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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Efficient Adabas Access 2 ADABAS Access READ PHYSICAL READ BY ISN (GET) READ LOGICAL FIND HISTOGRAM...

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