From the docs we wrote:

/**
* configures the size database files should grow in bytes, when no
* free slot is found within.
* <br><br>Tuning setting.
* <br><br>Whenever no free slot of sufficient length can be found
* within the current database file, the database file's length
* is extended. This configuration setting configures by how much
* it should be extended, in bytes.<br><br>
* This configuration setting is intended to reduce fragmentation.
* Higher values will produce bigger database files and less
* fragmentation.<br><br>
* To extend the database file, a single byte array is created
* and written to the end of the file in one write operation. Be
* aware that a high setting will require allocating memory for
* this byte array.