Actually, I believe that this layer would work fine as it is already. The 'message' table links a messageblk to a mailbox. It could easily be that a single messageblk is referenced by several rows in the message table and therefore appears in several people's mailboxes.
Aaron On Mon, 31 Mar 2003, Magnus Sundberg wrote: > Hello Jeff, > From your database design it looks like that you change the > mailbox_idnr record in the messages table when you move mail from one > mailbox folder to another. I hope this is possible at least by the IMAP > protocoll? > > The problem as I see it is the relational database structure itself. You > have this pointing relation MESSAGEBLK->MESSAGE->MAILBOX->USERS, quite > the opposite to when you are programming linked trees on a computer. > > I beleive you could achevie this by another database layer, one for each > user and messageblk. Let's divide the messageblk into two parts > msgblkptr (MessageBlockPointer) and msgblkdata (MessageBlockData). > The pointer is unique for every user and points to the Data. > So if you send 1000 people a message you will get 1000 pointers, but > just one datablock. > When you delete a pointer, you check if there are any more pointers to > the block, if the ointercount is zero, you also delete the data block. > > What is wrong with my reasoning? > > Except for that this will be difficult to merge into the installed base. > > What will the performance hit be? > > Is it worth the effort of changing? > > Please explain the problem of crosslinking. > > Is this one of exchanges weak points? > > /Magnus > > Jeff Brenton wrote: > > Hello Magnus, > > > > MS> Is there one new MESSAGEBLK created in the database for each user for > > MS> these messages, or is the MESSAGEBLK shared between the users. > > > > Yes, there is a complete message (1 entry into message and 2 or more > > into messageblk tables) for each recipient. Send a message to 1,000 > > people on the system, and 1,000 copies of it exist. > > > > The only system that does NOT do that, to my knowledge, is Exchange > > Server; it maintains a separate table internally to keep track of > > which users have seen/deleted the message, and doesn't actually delete > > it until ALL have seen it. > > > > While this is more space efficient, it is also a nightmare if certain > > users decide to move the message to one of their mailbox folders > > (maintained on the server, rather than on their local machine), > > because the copy makes a new link... message bodies can be cross > > linked endlessly, making problems if you ever need to restore the > > database. > > > > At least some backup procedures "fix" this by saving individual > > "snapshots" of the tables, so you end up with a backup containing a > > complete copy of these group messages for each user who hasn't purged > > it from their mailbox, and the restore ends up having multiple copies > > anyway... > > > > > > > _______________________________________________ > Dbmail mailing list > Dbmail@dbmail.org > https://mailman.fastxs.nl/mailman/listinfo/dbmail >
