What could cause Firebird to silently turn calculated fields into "normal" fields?

I'm using Firebird 2.5.8 to store information for a software I designed.

A customer contacted me today to inform me of multiple errors that I couldn't understand, and I used the "IBExpert" tool to inspect its database.

To my surprise, all the calculated fields had been transformed into "standard" fields. This is clearly visible in the "DDL" tab of the database tool, which displays tables definition as SQL code.

For instance, the following table definition:

CREATE TABLE TVERSIONS (
   ...
    PARENTPATH COMPUTED BY (((SELECT TFILES.FILEPATH FROM TFILES WHERE ID = TVERSIONS.FILEID))),
    ....
    ISCOMPLETE COMPUTED BY ((((SELECT TBACKUPVERSIONS.ISCOMPLETE FROM TBACKUPVERSIONS WHERE ID = TVERSIONS.CVERSION)))),
    CDATE COMPUTED BY (((SELECT TBACKUPVERSIONS.SERVERSTARTDATE FROM TBACKUPVERSIONS WHERE ID = TVERSIONS.CVERSION))),
    DDATE COMPUTED BY (((SELECT TBACKUPVERSIONS.SERVERSTARTDATE FROM TBACKUPVERSIONS WHERE ID = TVERSIONS.DVERSION))),
   ...
);

has been "changed" in the client database into this:

CREATE TABLE TVERSIONS (
   ...
    PARENTPATH VARCHAR(512) CHARACTER SET UTF8 COLLATE UNICODE,
    ...
    ISCOMPLETE SMALLINT,
    CDATE TIMESTAMP,
    DDATE TIMESTAMP,
    ...
);

How can such a thing be possible?

I've been using Firebird for more than 10 years, and I've never seen such a behavior until now. Is it possible that it could be a corruption of RDB$FIELDS.RDB$COMPUTED_SOURCE fields?

What would you advise?

Solution

To summarize the discussion on firebird-support (and comments above):

The likely cause of this happening is that the database was backed up and restored using gbak, and the restore did not complete successfully. If this happens, gbak will have ended in an error, and the database is in single shutdown state (which means only SYSDBA or the database owner is allowed to create one connection). If the database is not currently in single shutdown mode, someone used gfix to bring the database online again in normal state.

When a database is restored using gbak, calculated fields are initially created as normal fields (though their values are not part of the backup). After data is restored successfully, those fields are altered to be calculated fields. If there are any errors before or during redefinition of the calculated fields, the restore will fail, and the database will be in single shutdown state, and the calculated fields will still be "normal" fields.

I recommend doing a structural comparison of the database to check if calculated fields are the only problem, or if other things (e.g. constraints) are missing. A simple way to do this is to export the DDL of the database and a "known-good" database, for example using ISQL (command line option -extract), and comparing them with a diff tool.

Then either fix the existing database by executing the necessary DDL to restore calculated fields (and other things), or create a new empty database, and move the data from the old to the new (using a datapump tool).

Also check if any data is missing. By default, gbak restores the data in a single transaction, so in that case either all data is present or all data is missing. However, gbak also has a "transaction-per-table" mode (-ONE_AT_A_TIME or -O), which could mean some tables have data, and others have no data.