Syncs: to -delnorm or not to -delnorm

The process responsible for synchronizing the database with the file system is called syncvoltodb(8). That process can be called by hand or by another program, such as userperms or dblogd(8). In all of these cases, the sync can be run with or without -delnorm option.

Important note:

Never use the -del flag with syncvoltodb(8) for it can be destructive. Always use -delnorm instead. However, as you have seen earlier, you can safely use a -del flag with userperms. In that instance, -del performs with userperms exactly as -delnorm performs with syncvoltodb(8).

Default behavior

A sync happens on a directory-by-directory basis. The idea is to get the database’s information on the folder’s contents to agree with what’s on the file system, and to do it as quickly as possible. Roughly, here is the procedure for each directory:

1.	Xinet looks at a given folder on the file system, which by definition is online, and asks:

What's the modification time?

2.	For the moment, Xinet stores that time.

3.	Then Xinet looks at the same folder in the database and asks:

Is the folder online?

4.	If it’s listed as offline in the database, Xinet will sync that directory and any files it contains.

5.	It it doesn't exist at all in the database, Xinet will sync that directory.

6.	Any subfolders inside are treated as a new folder (for example., the questioning process starts over.)

7.	If the folder is listed as online, Xinet won’t sync it (yet). Instead it will ask a further question:

Is the modification time of the folder (according to the database) the same as the modification time on the file system?

8.	If the modification times are the same, then Xinet doesn’t sync that folder or the files it contains. If the modification times are different, Xinet will sync the folder and its files. Again, any subfolders are treated as new folders.

The idea here is to prevent synchronizing directories where nothing has changed (which is very common.) Any change made to the files inside a folder (renaming, removing, adding) will also update the modification time of the folder itself. Therefore, it’s safe to assume that a folder whose modification time is identical to that in the database doesn't contain files that have been changed since the last sync/update of the database.

In sum, Xinet only synchronizes the contents of a folder if there is a disagreement between the file system and the database about the folder’s online status or its modification time.

There is also one exception to note: when a file has been modified by an application other than Photoshop, the directory’s modification time is not updated. That sort of change will escape the method described above. Therefore, Xinet also checks file modification dates in all directories. Upon finding a file modification discrepancy, Xinet will update that file.

Using -delnorm

The -delnorm flag sets files to Online=3, but not offline—they still show online to people browsing. If there are subfolders, they are turned off one at a time in a recursive sync to copy paths down the file system tree.

In releases before 19.2, this option set all files across all folders offline by default, recursively down the tree (Online=0).

Setting files off ensures that the syncvoltodb(8) will synchronize every file in the folder without exception. There should be nothing different between the database and the file system after a
-delnorm sync.

Not using -delnorm

A sync run without a -del or -delnorm simply uses the procedure outlined in the "Default behavior” on page 682.

This type of sync is designed to catch changes made to the file system that evaded dblogd(8), and to do it quickly.

Typical operations that do not use a -delnorm include:

•	Resubmitting a volume in the Volumes tab without changing any of the options.

•	Scheduled synchronizations

•	Synchronizations run by listdir on the directory being displayed.

Syncs run without a -delnorm flag have one big flaw, known as the “cover-up” case. Normally, any change made to the file system (via SMB, NFS, or Unix) will cause a modification time discrepancy for the folder, thus setting up this directory to be synchronized when a sync is run. However, the modification time discrepancy can be covered up. Consider this scenario:

	TIME RECORDED IN:
Activity	File system	Database
Directory modification time	2 pm	2 pm
1. File added via ksd(1M)
Directory modification time	3 pm	3 pm
2. File added via Unix at 4 pm
Directory modification time	4 pm	3 pm
At this point, a sync (without a -del) will notice the modification time discrepancy and sync this directory.
3. File added via ksd(1M)	5 pm	5 pm
At this point, a sync (without a -del) will not find a modification time discrepancy and will not sync this directory.

So whatever files where added at 4 pm via Unix or SMB will not be added to the database when the sync happens. The only option is to run a syncvoltodb -delnorm on that directory (or a directory above it). As you can see, this adds an element of chance as to whether files will be caught by the sync or not.