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Efficient Adabas Access

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LAST-NAME = BROWN' OR JONES' Complex FIND (algorithm 4) ... Access Inverted List for ADAMS', BAKER', CHARLES', DAVENPORT', and DAVIS' ... – PowerPoint PPT presentation

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Title: Efficient Adabas Access


1
Efficient Adabas Access
2
ADABAS Access
  • READ PHYSICAL
  • READ BY ISN (GET)
  • READ LOGICAL
  • FIND
  • HISTOGRAM

3
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

4
ADABAS Access -READ PHYSICAL
  • Access to Data Storage only.
  • Records returned in the order they are stored
    physically in Data Storage

5
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

6
ADABAS Access - READ BY ISN
  • Access to Address Converter Data Storage
  • Records returned in ascending ISN order

7
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

8
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

9
ADABAS Access - READ LOGICAL
10
Natural Commands
FIND
Memory
1 or 1
4 or 4
Inverted List
Work
Address Converter

2
Data Storage
3
11
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

12
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

13
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

14
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

15
ADABAS Access - FIND
FIND PERSONNEL WITH NAME ADAMS
16
ADABAS Access - FIND
FIND PERSONNEL WITH NAME ADAMS
Access Inverted List for value ADAMS. Results in
ISN list of 2, 7, 9, 12
17
ADABAS Access - FIND
FIND PERSONNEL WITH NAME ADAMS
Access Address Converter to obtain RABN.
18
ADABAS Access - FIND
FIND PERSONNEL WITH NAME ADAMS
Access Data Storage to retrieve record.
19
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!

20
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.

21
Natural Commands
HISTOGRAM
Inverted List
  • Use when only descriptor, sub-descriptor or
    super descriptor components needed
  • Use for validation of data

22
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
23
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

24
Direct Calls
How records are accessed by ADABAS
Direct Call Action Performed L1
READ by ISN L2
READ physical L3 READ
logical L9 HISTOGRAM
25
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
26
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
27
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

28
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.

29
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