![]() ![]() Maybe this should go in a new section? Even as common as you say it is, it's a little more complex and so maybe shouldn't be the first example. the homegrown database I use at work doesn't even allow upgrading a lock from shared to exclusive.As a side effect, I never upgrade the lock. I'm cautious about changing things based on a non-repeatable read, so if I do a select then update, I always do "select. in general, I use fancy MVCC databases in the read committed isolation level.That one resource is enough to model communication, and communication is enough to model a scenario where process A and B are mutually waiting for the other to send a message. In hindsight, I think I've only avoided getting bitten by this because,ĭeadlock -in the general sense- is just processes waiting for each other and can always occur even with one resource. Burt Harris 15:42, 24 August 2006 (UTC) Reply īurt: I'm sold I think your explanation belongs in the article. ![]() In my experience, at least for databases, this form of deadlock is far more common in practice than a "classic" deadlock involving two seperate resources. Unfortunatly reader-writer locks can introduce a deadlock condition sometimes called a conversion deadlock, where two threads both obtain a read lock on the resource, and then attempt to convert it to a write lock. Slamb 20:37, 20 August 2006 (UTC) Reply ĭiagree w/ Matthew & Slamb In practice, most database systems can deadlock on what seems to be a single resource, and independent of granularity (table, row, etc.) This is due to the use of a reader-writer lock, used to improve concurrency. catch the "would deadlock" exception generated by the database server and replay the transaction.I'd say it's better to use a per-row example like the PostgreSQL one and suggest resolving it application-side in one of two ways: (But this particular type of deadlock is easily prevented, e.g., by using an all-or-none resource allocation algorithm.)Īre you proposing something like LOCK table_1, table_2 IN EXCLUSIVE MODE at the beginning of the transaction? That severely limits concurrency. I'd say this is a better example than two tables, because it's best to avoid contributing to the perception that databases use table-level locks internally. PostgreSQL's documentation describes this. I'd guess the original writer had encountered a deadlock with row-level locking and misunderstood. I'm giong to replace this with a better example MatthewWilcox 12:55, (UTC)Īgreed deadlock is impossible with only one resource, which is what that text describes. Just give it to one of the clients which will run and finish, then the other one gets a chance to run. ![]() In this case both clients will wait for the lock forever. If two client applications both attempt to lock the same table at the same time, neither will receive it, there is no general way to decide who to give the lock to. Client applications using the database may require exclusive access to a given table, and in order to gain exclusive access they ask for a lock. Preceding unsigned comment added by 47.23.40.34 ( talk) 17:00, 18 April 2017 (UTC) Reply Īn example of a deadlock occurs frequently in database products. Then there is a "Deadlock" disambiguation page, which has no references to "Deadly Embrace" either. I was looking for the film "Deadly Embrace" and was redirected here, with no explanation as to why. Reply Why, "Definitely not?" Software developers from England with whom I have worked said "deadly embrace" more often than they said "deadlock." Also, I'm sure I have read at least one book whose author thought that "deadly embrace" was the special case of a deadlock between just two processes/threads/etc. Shouldn't this article have the term "Deadly Embrace" somewhere in it as an alternate term for Deadlock? - grr 23:12, 12 December 2006 (UTC) Reply. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |