Efficient Adabas Access
ADABAS Access
* Select the correct access method.
* Code it efficiently.
•
•
•
•
•
2
READ PHYSICAL
READ BY ISN (GET)
READ LOGICAL
FIND
HISTOGRAM
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
3
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
* Order of records returned: 2,1,14,3,5,12,4,6,7,8,11,9,20,21
4
Natural Commands
READ by ISN
Address
Converter
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
5
ADABAS Access READ BY ISN
• Access to Address Converter & Data Storage
• Records returned in ascending ISN order
125
128
128
6
125
126
…
126
0
127
125
126
0
127
0
127
0
127
0
128
0
0
128
Natural Commands
READ Logical
1
2
4
Inverted List
Address
Converter
Data Storage
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
7
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
8
ADABAS Access - READ LOGICAL
LAST-NAME
ADAMS
BAKER
BROWN
CARLSON
2
0
0
1
0
…
4
0
1
0
COUNT
3
1
2
3
2
0
2
0
ISNS
5
9
2
4
1
3
4
0
6
7
1
0
8
3
0
2 ADAMS 4 BAKER 8 CARLSON FREE
PADDING
1 BROWN
6 BROWN 5 ADAMS PADDING
9 ADAMS
3 CARLSON
9
FREE
7 CARLSON
FREE
0
0
Natural Commands
FIND
Memory
1
or
1
Inverted List
4
or
4
Work
Address
Converter
2
3
10
Data Storage
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 > 51 will
generate I/O to work part 3
• Complex FINDs can generate I/O to work part 2
11
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 > #AGE
AND SEX = #SEX AND VET-STATUS = ‘V’
12
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
13
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
14
ADABAS Access - FIND
FIND PERSONNEL WITH NAME = ‘ADAMS’
Value
ADAMS
BAKER
CHARLES
DAVENPORT
DAVIS
125
128
128
15
Count
4
3
3
2
2
125
126
…
----------------------ISNs----------------------------------------------------------------------------------
2
7
9
12
…
1
3
20
5
6
8
11
21
4
14
126
0
127
125
126
0
127
0
127
0
127
0
128
0
0
128
ADABAS Access - FIND
FIND PERSONNEL WITH NAME = ‘ADAMS’
Value
ADAMS
BAKER
CHARLES
DAVENPORT
DAVIS
125 125
128 126
128 …
16
Count
4
3
3
2
2
126
0
----------------------ISNs----------------------------------------------------------------------------------
2
7
9
12
…
1
3
20
5
6
8
11
21
4
14
Access Inverted
List for value
ADAMS.
127
125
126
0
127
0
127
0
Results in ISN list
127
of 2, 7,1289, 12 0
0
0
128
ADABAS Access - FIND
FIND PERSONNEL WITH NAME = ‘ADAMS’
Value
ADAMS
BAKER
CHARLES
DAVENPORT
DAVIS
125
128
128
17
Count
4
3
3
2
2
125
126
…
----------------------ISNs----------------------------------------------------------------------------------
2
7
9
12
…
1
3
20
5
6
8
11
21
4
14
126
0
127
125
126
0
127
0
127
0
127
0
128
0
0
128
Access Address
Converter to
obtain RABN.
ADABAS Access - FIND
FIND PERSONNEL WITH NAME = ‘ADAMS’
Value
ADAMS
BAKER
CHARLES
DAVENPORT
DAVIS
125
128
128
18
Count
4
3
3
2
2
125
126
…
----------------------ISNs----------------------------------------------------------------------------------
2
7
9
12
…
1
3
20
5
6
8
11
21
4
14
Access Data
Storage to
retrieve record.
126
0
127
125
126
0
127
0
127
0
127
0
128
0
0
128
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!
19
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.
20
Natural Commands
HISTOGRAM
Inverted List
• Use when only descriptor, sub-descriptor or super
descriptor components needed
• Use for validation of data
21
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
F
M
22
Count
234
293
1. Returns value
of ‘F’ and
-----------ISNs------------------------------------------------------------------------------------------------------------------
2
3
7
9
10
11
15
16
17
21
25
=18 23419 20
1
4
5
6
8
12*NUMBER
13
14
…
…
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
23
Direct Calls
How records are accessed by ADABAS
24
Direct Call
Action Performed
L1
READ by ISN
L2
READ physical
L3
READ logical
L9
HISTOGRAM
Direct Calls
How records are accessed by ADABAS
25
Direct Call
Action Performed
L4
READ by ISN w/ hold
L5
READ physical w/ hold
L6
READ logical w/ hold
Direct Calls
How records are accessed by ADABAS
26
Direct Call
Action Performed
S1
FIND
S4
FIND w/ hold
A1/A4
UPDATE
N1/N4
STORE
E1/E4
DELETE
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
27
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
?
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