I spent half of yesterday editing (in the old fashioned sense of the word) labeling photos both by star and color within a folder holding several thousand images. Last night at shutdown, Lightroom froze and would not unfreeze. I finally had to do a force quit. When I started my iMac again this morning and opened Lightroom back up, the entire half days worth of work was gone. All the star and color labels had disappeared. Lightroom does not have a "save" feature to preserve labeling. The only way I can find to do so is to close Lightroom every now awhile still working with it and then open it back up. This is an unnecessary pain. Adobe needs to put a "save" in Lightroom that will preserve these edits. An auto save would be great, also.
Crash or freeze, Feature request, How to, Mac, Performance, Problem or error
As you make changes, the changes are immediately written to the database (catalog). There is a layer of caching to improve disk performance. What is needed is a way to force the database cache to the flushed to disk. The way I do this is to pick an action that is going to return a large amount of data so that the dirty cache pages are swapped out for clean ones. Normally I do this by selecting a folder with a large number of images and then scroll through the results.
Closing Lightroom and restarting it will also get the job done, but seems like overkill most of the time.