Hi,
Thanks for the quick and detailed reply! This mailing list is a great help.
I have a follow-up question: You say that Neo4j "will synchronize
access between concurrent transactions (on a node and relationship
level)". I am a bit curious about the granularity of the
synchronization on the node/relationship level.
Is every node an isolated resource in this sense? That is, if I modify
properties of node A and properties of node B the modifications will
not block each other? Even if they are connected with a relation?
How about relations? Can modifying or creating a relation also lock
either of the two nodes it connects?
Best regards,
Thomas
On Wed, Feb 10, 2010 at 1:23 PM, Johan Svensson <jo...@neotechnology.com> wrote:
> Hi,
>
> On Wed, Feb 10, 2010 at 10:48 AM, Thomas Andersson
> <greddbul...@gmail.com> wrote:
>> Hi,
>> ...
>> // don't do this
>> synchronized void methodA()
>> {
>> nodeA.setProperty( "prop1", 1 );
>> methodB();
>> }
>>
>> synchronized void methodB()
>> {
>> nodeB.setProperty( "prop2", 2 );
>> }
>>
>> According to the test, "The code above is very deadlock prone when
>> methods A and B are called concurrently.".
>>
>> Exactly why is that? I try to understand what the situation is that
>> should be avoided, but when I run the code in my head I can't figure
>> out when and why the deadlock occurs.
>
> All Neo4j API operations must be invoked within a transaction and the
> modifying operations (such as Node.setProperty) will synchronize
> access between concurrent transactions (on a node and relationship
> level). I updated the wiki with a link to
> http://wiki.neo4j.org/content/Transactions#Isolation that explains
> this a bit better.
>
> To give you a deadlock scenario with the code above:
>
> - tx1 modifies nodeB
> - tx2 calls methodB but blocks on nodeB.setProperty
> - tx1 calls methodA and will then block when trying to call methodB
> - deadlock that can not be detected by the Neo4j kernel
>
> Regards,
> -Johan
> _______________________________________________
> Neo mailing list
> User@lists.neo4j.org
> https://lists.neo4j.org/mailman/listinfo/user
>
_______________________________________________
Neo mailing list
User@lists.neo4j.org
https://lists.neo4j.org/mailman/listinfo/user
