After a file is copied during backup the size is requested from the storage in case it differs from what was written so that repo-size can be reported accurately. This is useful for situations where compression is being done by the filesystem (e.g. ZFS) and what is stored can differ in size from what was written.
In S3 the reported size will always be exactly what was written so there is no need to check the size and doing so immediately can cause problems because the new file might not appear in list commands. This has not been observed on S3 (though it seems to be possible) but it has been reported on the Swift S3 gateway.
Add a driver capability to determine if size needs to be called after a file is written and if not then simply use the number of bytes written for repo-size.
Reported by Matt Kunkel.
Scanning the entire backup directory can be very expensive if there are a lot of small tables. The backup manifest contains the backup directory list so use it to perform syncs instead of scanning the backup directory.
Refactor storage layer to allow for new repository filesystems using drivers. (Reviewed by Cynthia Shang.)
Refactor IO layer to allow for new compression formats, checksum types, and other capabilities using filters. (Reviewed by Cynthia Shang.)
