Den 02.12.2015 13:24, skrev Ann Harrison [email protected] [firebird-support]: >> On Dec 2, 2015, at 6:35 AM, Tim Ward [email protected] [firebird-support] >> <[email protected]> wrote: >> >> What about if two concurrent transactions are both trying to *delete* >> the *same* record at once? - from the point of the view of the user's >> objectives there's no reason why this shouldn't work, as either way the >> record is going to end up deleted, which is what the user wants, but >> would I be right in guessing that Firebird isn't that clever, and that >> deadlocks are possible in this scenario? > It's not nearly that simple. What would happen if one of those transactions > rolled back? > > Good luck, > > Ann Logically, I don't see any difference between an update and a delete. If two transactions that had done nothing possibly excepting reading the record simultaneously tried to delete the same record, I would expect one of them to succeed and the other to get a lock conflict (not the same as a deadlock, but many persons, probably including you, use the term deadlock when they mean lock conflict).
One way to avoid this particuar kind of lock conflict, would be to not delete the record directly from the clients, but rather insert it into a table that you e.g. could call DELETED. Never let any user directly delete from the DELETED table, but have a housekeeping routine that at regular intervals delete records (from both your main table and the DELETED table). I.e. similar to what is sometimes done with extra tables having COUNTs and inserting new records with +1 or -1 when adding or removing items. Though I must admit I've never heard of anyone using this technique for DELETE. Set ------------------------------------ ------------------------------------ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Visit http://www.firebirdsql.org and click the Documentation item on the main (top) menu. Try FAQ and other links from the left-side menu there. Also search the knowledgebases at http://www.ibphoenix.com/resources/documents/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ------------------------------------ Yahoo Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/firebird-support/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/firebird-support/join (Yahoo! ID required) <*> To change settings via email: [email protected] [email protected] <*> To unsubscribe from this group, send an email to: [email protected] <*> Your use of Yahoo Groups is subject to: https://info.yahoo.com/legal/us/yahoo/utos/terms/
