Multiple (serialized) writers to calibre library

[k_b]

The problem (not original): Several people contributing new books, metadata and content fixes &c to a "common" calibre library.

Known: calibre does not support multiple simultaneous access.

Best solution I've come up with:

1. Each person has a private library and calibre instance for adding and editing books; these libs typically stay very small, with updates delivered back to the common library on roughly a daily basis. Never access the common lib from private instance (too much chance of accidental corruption).
   
   I've put these in VM's on a Hacintosh server (wife's UI requirement) to simplify sharing issues, since things like NAS's and file servers seem to be high risk for calibre. I can easily update caliber on all the VM's, and VM's are easier to sanitize if the kids/wife go to dangerous sites (yeah, they do - got a squid server too, but stuff still gets by it).
   
   
2. Common library on Hac server with a mutex wrapper, owned by separate calibre user and writable only by owner; everybody can start it, but only one server instance can be running at a time, and it is only used to deliver books from private library, verify delivery, and quit.
   
   This is a manual step that I would love to automate. I've tested rsync and metadata rebuild, and haven't seen any problems, but haven't gone there yet.
   
   In truth, the common library instance would be used, w/ forewarning, for any major metadata overhauls, but that's a rare event. Haven't added a custom column since, oh, January?
   
3. Content server is used to pull books from the common lib to local instances for editing &c. (again, avoids ever referencing the common lib from a personal instance).
   
   We use a common set of tags for typical editing tasks, so it's easy to grab all the recent "format error X" titles and do them in batches. I get stuck with all the regex hacking.
   
   Content server is also how books get typically get loaded on to the various ereaders.
   
   

Beyond that, standard set of hourly backups, nightly rsync of complete library and such.

The one noted gap here is having a calibre library that matches the books on my kindle (can't fill "books on device" column unless I plug the kindle into the Hac server), for quickly adding comments &c. Easy enough to work around, but I used that column more than I realized.

Comments, critiques, suggested improvements more than welcome. I have no problems maintaining this, but simpler and more automated would always be better.