Drive synchronization caches consolidated directory checksums in the database. While this has previously been one checksum per folder, this has changed over time after different views on directories needed to be considered for clients sending different file exclusion filters. If a client uses some filters only temporarily, associated checksums are no longer needed at all and may be removed again.

To prepare the removal of no longer used directory checksums from the database, a new column is inserted into the table driveChecksums, with the following defintion:

> BIGINT(20) NOT NULL DEFAULT 0

Existing cached checksums are purged during that process to ensure that newly added ones are equipped with a real value directly.