# Automatic De-fragmentation of Dynamic Database Objects

> If a class contains dynamically extended components (i.e. fields of type `string`, `vector`, `varbinary` and `sequence`), an object of this class that is frequently updated can develop memory holes. To prevent this kind of fragmentation, an automatic de-fragmentation (`auto_compact` mode) feature is provided via a database parameter `autocompact_threshold`.

> If the size of an object exceeds this `autocompact_threshold` value, then the automatic de-fragmentation algorithm reallocates objects, eliminating any internal fragmentation.