The transaction log file for the Apex Central database is …\data\db_ApexCentral_log.LDF. SQL Server generates the transaction log as part of its normal operation.
db_ApexCentral_log.LDF contains all managed product transactions using db_ApexCentral.mdf.
By default, the transaction log file has no file size limit on the SQL Server configuration. This leads to filling up the available disk space.