Efficient Adabas Access

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Efficient Adabas Access
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ADABAS Access

• READ PHYSICAL
• READ BY ISN (GET)
• READ LOGICAL
• FIND
• HISTOGRAM

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Natural Commands
READ 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

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Natural Commands
READ by ISN
Data Storage
Address Converter

• 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

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ADABAS Access - READ BY ISN

• Access to Address Converter Data Storage
• Records returned in ascending ISN order

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Natural Commands
READ Logical
1
Inverted List
4
Data Storage
Address Converter
2
3

• 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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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
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Natural Commands
FIND
Memory
1 or 1
4 or 4
Inverted List
Work
Address Converter

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Data Storage
3
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Natural Commands
FIND

• 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 gt 51 will
  generate I/O to work part 3
• Complex FINDs can generate I/O to work part 2

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Natural Commands
FIND

• Simple find (algorithm 1)
• LAST-NAME BROWN
• Moderate complexity (algorithm 2)
• LAST-NAME BROWN OR JONES
• Complex FIND (algorithm 4)
• FIND PERSONNEL WITH AGE gt 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 gt 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 - FIND
FIND PERSONNEL WITH NAME ADAMS
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ADABAS Access - FIND
FIND PERSONNEL WITH NAME ADAMS
Access Inverted List for value ADAMS. Results in
ISN list of 2, 7, 9, 12
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ADABAS Access - FIND
FIND PERSONNEL WITH NAME ADAMS
Access Address Converter to obtain RABN.
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ADABAS Access - FIND
FIND PERSONNEL WITH NAME ADAMS
Access Data Storage to retrieve record.
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ADABAS Access - FIND
FIND IN PERSONNEL WITH LAST-NAME ADAMS THRU
DAVIS

• 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!

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ADABAS Access - FIND

• Should only be used if no work file I/O is
  involved (lt51 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 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 even though
  theyre in the inverted lists.

1. Returns value of F and 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 Calls
How 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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Direct Calls
How records are accessed by ADABAS
Direct Call Action Performed L4
READ by ISN w/ hold L5
READ physical w/ hold L6
READ logical w/ hold
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Direct Calls
How records are accessed by ADABAS
Direct Call Action Performed 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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Questions

• ?