Subject Re: [ib-support] Interbase 4.1 to firebird
Author Helen Borrie
At 12:44 AM 14-06-02 +0000, you wrote:
>I am currently going through our company program and making changes
>where need be for moving to firebird (InterBase 6.5). Since Firebird
>has the different dialects and it seems that InterBase 4.1 is a
>dialect 1. Is it possible that if something goes wrong, I can get
>back to InterBase 4.1.

No. Each major version has a different on-disk structure (ODS). v.4 is
ODS 8, v.5 is ODS 9 and Firebird is ODS 10. You change the ODS by backing
up the older version with its own version of gbak and then restoring with
the newer version's gbak.

So - if you think something is going to go wrong that you don't want to fix
in the new environment, make certain you provide a fallback strategy. Do
proof-of-concept testing with copies, not live data.

The reason Firebird (ODS 10) has the concept of dialects is that, between
ODS 9 and ODS 10 there were some major changes to data types - notably the
DATE type being replaced with TIMESTAMP and a new DATE type being
introduced which stores date only, and very significant changes to
numerical types with the introduction of the 64-bit integer. Dialect 1
provides compatibility with ODS 8 and 9, dialect 2 is a client-only state
where you can perform changes to your structures to transit to dialect
3. Dialect 3 provides the full range of support for ODS 10.

You can run an ODS 9 database under Firebird server and access it with the
matching Firebird client API, without altering the
on-disk-structure. Theoretically, Firebird server won't work with an ODS 8
database, but I have heard of cases where it did.

I think you have plenty of scope for proving the concept and deciding on a
dialect. It's highly doubtful that there would be anything that would give
rise to the necessity of reverting to ODS 8; but cover your back by taking
sensible precautions.


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