Please enable JavaScript to view this site.

A-Shell Reference

Navigation: Development Topics > ISAM-A

Specifications & Features

Scroll Prev Top Next More

Updated November 2018; see History

The following table lists various sizes, capacities and limits for ISAM-A files and processing. Note, however, that some of these limits have been arbitrarily set just for efficiency. If you have legitimate need for larger limits, contact us. Also note that where the word "extension" appears in the table below, this indicates a feature that was not present in the AMOS version and which may require some modification to your application; see A-Shell Extensions for more details.

Item

Size / Limit /
Capacity / Comment

Updated in A-Shell
build; old value

Record size

16K

988 of Dec 07; 8K

Number of keys per record

20

 

DAT file size

2 terabytes

4.9.948; 2GB

IDX file size

2 terabytes (theoretical)

5.1.1134; 2GB

Records per file

2 ^ 31

 

Bytes per key

120

 

Parts (fields) per key

20

 

Duplicate keys

65536

 

Compressed keys

yes (optional, extension)

 

Compressed data records

yes (optional, extension)

 

Transaction support

yes Linux, no Windows

 

File recovery from log

yes Linux, no Windows

 

Audit trail

maybe; under review

 

Auto expansion of file

yes

 

Index rebuild utility

yes

 

Index verification utility

yes

 

Add/delete index without dump/reload

yes

 

ODBC / OLEDB / SQL access

yes via third party utilities

 

 

History

November 2018, A-Shell 6.5.1650:  • Enable variable length records in the Windows version (matching Unix); • Increase the maximum number of key parts from 8 to 20, and the maximum key length from 80 to 120, in the Unix version (matching Windows). Note: the only outstanding difference between the two versions is that the Windows version doesn't support transaction logging. Also note: these changes update the ISAM-A version, as displayed by the ISMUTL header, to 6.11r.