Hi and thanks for the answer, By close transaction I mean commit. The code as it is does not share transactions.
The problematic use case is: T1 begin create rel 0 -> 1 T1 commit T1 begin create rel 1 -> 2 T2 begin create rel 0 -> 3 <<<<<< deadlock set property 3 T2 commit T1 set property 2 T1 commit The case that works (with 0 -> 1 and 0 -> 3 already created): T1 begin obtain 0 -> 1 obtain 1 T1 commit T1 begin create rel 1 -> 2 T2 begin obtain 0 -> 3 set property 3 T2 commit T1 set property 2 T1 commit The goal is having 0 -> 1 -> 2 and 0 -> 3 created. I suspect the problem lies within node 0. Is it possible that T1 locks 0 when creating 1 -> 2? Regards, -- Daniel Martínez El mié, 11-11-2009 a las 14:13 +0100, Johan Svensson escribió: > Hi, > > There is no global lock in Neo4j. We lock on a relationship and node level so: > > create node - write lock on created node (so other tx can't see until > it exist for real) > set/remove property - write lock on either the node or relationship > create / delete relationship - write lock on the relationship and both > nodes it is connected to > > There is however a special case during relationship create/delete. For > a short period of time (during commit) a write lock may be grabbed on > some other relationship (connected to the same node) while updating > the "dual interleaved linked list" storing the relationships. > > I could not quite understand the use case you describe. By close you > mean commit/rollback or suspend of transaction? If close means commit > I get: > > T1 begin > create rel 0 -> 1 > T1 commit > T1 begin > create rel 1->2 > T2 begin > setProperty 2 // this will block since other open tx has created > relationship to node 2 > > When T1 commits T2 can continue. > > Regards, > -Johan > > On Wed, Nov 11, 2009 at 12:57 PM, Daniel Martínez > <[email protected]> wrote: > > Hi everyone, > > > > I am currently testing neo4j (1.0-b9)as a persistence layer for an app. > > I have encountered an strange problem. > > > > I have two threads creating relations at the same time (both open > > transactions) > > > > (0 is root node) > > > > T1(main): Begin transaction --> create relationship 0 -> 1 --> Close > > Transaction --> Begin transaction --> create relationship 1 -> 2 --> > > create T2 --> wait for T2 --> set property 2 --> .... --> Close > > Transaction --> .... > > T2: Begin transaction --> create relationship 0 -> 3 --> set property 3 > > --> Close Transaction > > > > T1 is waiting for T2 to end, but it never does because of a deadlock. > > Why is there such a deadlock? The nodes are not the same (concurrent > > transactions for 1->2 and 0->3 creation). > > > > This does not occur during this situation > > (0->1, 0->3 exist in database, 0 is root node) > > > > T1(main): Begin transaction --> obtain node 1 --> Close Transaction --> > > Begin transaction --> create relationship 1->2 --> create T2 --> wait > > for T2 --> set property 2 --> .... --> Close transaction --> .... > > T2: Begin transaction --> Obtain 3 --> set property 3 --> Close > > Transaction > > > > In this case both transactions commit correctly. > > > > Is there a global lock in neo4j when creating relationships? > > > > Thanks for your help, > > -- > > Daniel Martínez > _______________________________________________ > Neo mailing list > [email protected] > https://lists.neo4j.org/mailman/listinfo/user ________________________ Soluciones de Gestión para su empresa eBusiness, ERP, CRM ________________________ Daniel Martínez Martínez Gerente C/ Julia García Boután, 29 28022 Madrid España E-mail: [email protected] Web: www.paradisosistemas.es Comercial: [email protected] Tel: 678416758 _______________________________________________ Neo mailing list [email protected] https://lists.neo4j.org/mailman/listinfo/user
