It is worth mentioning this exception in the context of applying referential integrity constraints, since it is a regular source of frustration for new users. Firebird will not allow a referential constraint to be added or dropped if a transaction is using either of the participating tables.
Sometimes it may be less than obvious to you just in what way the object is in use. Other dependencies —such as stored procedures or triggers that refer to your tables, or other referential constraints affecting one or both—can cause this exception to occur if they are in use by an uncommitted transaction. Metadata caches (blocks of server memory that hold metadata used to compile recent client requests and any recently used stored procedure and trigger code) keep locks on the objects in their possession. Each connection has its own metadata cache, even on a Superserver, so the server could be holding locks on objects that no connection is actually using.
It is highly recommended that you get exclusive access to the database for any metadata changes, particularly those involving dependencies.
Firebird Related Interview Questions
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Introduction To Client/server Architecture
About Firebird Data Types
Date And Time Types
Blobs And Arrays
From Drawing Board To Database
Creating And Maintaining A Database
Firebird’s Sql Language
Expressions And Predicates
Querying Multiple Tables
Ordered And Aggregated Sets
Overview Of Firebird Transactions In
Programming With Transactions
Introduction To Firebird Programming
Developing Psql Modules
Error Handling And Events
Security In The Operating Environment
Configuration And Special Features
Interactive Sql Utility (isql)
Database Backup And Restore (gbak)
Housekeeping Tool (gfix)
Understanding The Lock Manager
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