[infinispan-issues] [JBoss JIRA] Commented: (ISPN-715) Eager locking a single node should only acquire a single lock

[Mircea Markus (JIRA)]

    [ https://jira.jboss.org/browse/ISPN-715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12558519#action_12558519 ] 

Mircea Markus commented on ISPN-715:
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thinking about it not sure how that would reduce number of deadlocks?
[14:57] mmarkus: or cause deadlocks
[14:58] an1310: ?
[14:59] an1310: You would only acquire the one lock.  If node A and node B both acquired a local lock, but we hashed to node C, wouldn't that be a deadlock?
[15:01] mmarkus: so we have tx1 running on A, tx2 running on B and both work on a key that's hashed to C
[15:01] mmarkus: is this your scenario?
[15:03] an1310: Yes, unless there's some way that I could tell my app to always go to C (since that's where the data lives).
[15:04] an1310: I'm colocating all the necessary caches involved in a tx on one data node and using that "eager lock single node" feature.
[15:04] an1310: ...data on a cache; typing too fast.
[15:04] mmarkus: returning to the example: how does that cause a deadlock?
[15:05] mmarkus: i.e. the fact that I also acquire a local lock on A and B for key "k" which is hashed to C
[15:06] an1310: I may be wrong about the deadlock part.
[15:08] mmarkus: I don't see the benefit of it. Actually I think it would even cause performance faults: if another tx3 runs on A and tries to acquire lock on "k" which is held by tx1 then it would have to go to C and only then to timeout. Right now it would fail fast, without need to go to C


> Eager locking a single node should only acquire a single lock
> -------------------------------------------------------------
>
>                 Key: ISPN-715
>                 URL: https://jira.jboss.org/browse/ISPN-715
>             Project: Infinispan
>          Issue Type: Feature Request
>            Reporter: Erik Salter
>            Assignee: Manik Surtani
>
> The new eager/explicit lock for a single node feature in 4.2.0 can be further optimized.  Right now, a local lock and a lock on the node where the key is hashed is acquired.  To increase throughput and minimize deadlock occurrences, we should only acquire the one lock (on the node).  
> (Obviously, if the key is hashed to the local node, the local lock and the node lock are one in the same).

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