Hmm, so if the database size is crucial to the player's ability to cache why don't we kill the comment field from the database altogether. The only time when the comments field is beeing used is when the details screen is beeing viewed, so i see no reason for it to be in the ram the whole time.
I understand that the player needs quick access to various song infos for its visuals and info screens, thus the database-in-ram concept, but the comments field ain't one of them. So .... couldn't we just make the details view read the actual ID3 tags from the harddisk? Maybe even all of the ID3v2 tags? The comment field is of particular interest to me, but maybe others have interest in seeing composer, org. artist etc fields in the details view?