Some users may find that SpiderOak ONE's application data folder grows to a large size. What you are seeing is ONE's internal database. This is on each of your computers and caches metadata about (but not the contents of) the files in your account for fast browsing, offline browsing, and to aid in deduplication. The more data you have stored in your account, the larger the database will become. You can expect this to occupy up to 1% of the space occupied in your online backup account.
When ONE is backing up files, the size of the database will temporarily increase by the size of those files. SpiderOak turns those files into encrypted data blocks, which occupy temporary space in the database. During the time that you are uploading a large file, ONE will need an amount of disk space equal to the size of that large file. Once those blocks are uploaded, the local copies are deleted and the database shrinks again. To accurately measure the size of the database, do so when ONE is shut down.
Over time any database can develop bloat. Whenever ONE notices that significant disk space can be saved by cleaning the database file, it will do so. Although ONE does a good job of taking care of this automatically, you can also trigger a manual cleanup at the command line if you wish with the