Re: [Neo4j] Number of nodes/relationships visited in query?

2011-04-11 Thread Stephan Hagemann 
Hi Tobias,

yes!

Since computation isn't performed until actually requested (when the
 iterator is iterated over), and since the Iterable could give a different
 result when you iterate over it subsequent times (due to the graph being
 modified), the Iterator object is the only object where I could see that
 such information could be added usefully. This does mean that you cannot
 use
 the java foreach loop with such an Iterable AND get the visited count, but
 would have to resort to using the hasNext() and next() methods. We could
 quite easily add some convenience methods for making that easier though,
 something like:

 CountIteratorPath pathIter = shortestPath.findAllPaths( start, end
 ).iterator();
 for ( Path path : IterUtil.loop( pathIter ) ) {
doSomethingWith(path);
 }
 // after the loop is done, number of nodes visited so far is the total
 number of visited nodes.
 int visitedNodes = pathIter.numberOfNodesVisitedSoFar();


This is exactly what I thought I would like to do! It would be fine for
numberOfNodesVisitedSoFar to hold the number for the nodes from the last run
of the iterator. I agree that it would be helpful to output it through the
REST API that way you could compare the efficiency and load of queries (I
will send you another email about exactly that in a bit...).


 WDYT? If this is useful we could add this kind of statistics to all types
 of
 traversals. Exposing that through the REST interface would be even simpler,
 the implementation would simply do the equivalent of the iteration above
 then add the statistics to the result. For paginated results (when those
 are
 added) we could have the statistics reflect the number of nodes visited for
 creating that page of data, for algorithms that find the easiest
 solutions
 first, you could use those statistics to stop a search when the number of
 nodes visited to collect a page grows too big.


I agree. Again, I believe, this would be genuinely helpful in a lot of
situations.

cu
Stephan
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[Neo4j] Number of nodes/relationships visited in query?

2011-04-10 Thread Stephan Hagemann 
Hi all,

is there a way for me to get to the number of nodes or relationships that
the graph algorithms (like ShortestPath) have visited and output it with the
result of the query? I would like to do that to analyze the performance and
load of query processing. Any ideas?

Thanks!

Stephan
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Re: [Neo4j] Number of nodes/relationships visited in query?

2011-04-10 Thread Tobias Ivarsson 
That information is not available at the moment. But it is an interesting
idea. How would you like to access it? Can you give a quick sketch of how
you envision the API for it.

Would it be something like this?

interface PathFinderP extends Path {
P findSinglePath( Node start, Node end ); // ok, nothing added here
// you'd have to use this version to get those statistics:
CountIterableP findAllPaths( Node start, Node end );
}

interface CountIterableT extends IterableT {
CountIteratorT iterator();
}

interface CountIteratorT extends IteratorT {
int numberOfNodesVisitedSoFar();
int numberOfRelationshipsVisitedSoFar();
}

(But with more thought through names)

Since computation isn't performed until actually requested (when the
iterator is iterated over), and since the Iterable could give a different
result when you iterate over it subsequent times (due to the graph being
modified), the Iterator object is the only object where I could see that
such information could be added usefully. This does mean that you cannot use
the java foreach loop with such an Iterable AND get the visited count, but
would have to resort to using the hasNext() and next() methods. We could
quite easily add some convenience methods for making that easier though,
something like:

CountIteratorPath pathIter = shortestPath.findAllPaths( start, end
).iterator();
for ( Path path : IterUtil.loop( pathIter ) ) {
doSomethingWith(path);
}
// after the loop is done, number of nodes visited so far is the total
number of visited nodes.
int visitedNodes = pathIter.numberOfNodesVisitedSoFar();

WDYT? If this is useful we could add this kind of statistics to all types of
traversals. Exposing that through the REST interface would be even simpler,
the implementation would simply do the equivalent of the iteration above
then add the statistics to the result. For paginated results (when those are
added) we could have the statistics reflect the number of nodes visited for
creating that page of data, for algorithms that find the easiest solutions
first, you could use those statistics to stop a search when the number of
nodes visited to collect a page grows too big.

Cheers,
Tobias

PS. I had a few other ideas on how such statistics information could be
added, but this was the least invasive of them. I sketched this up in five
minutes (after half a bottle of wine), so I'm very open to the possibility
of there being more elegant ways of adding this information.

On Sun, Apr 10, 2011 at 10:45 PM, Stephan Hagemann 
stephan.hagem...@googlemail.com wrote:

 Hi all,

 is there a way for me to get to the number of nodes or relationships that
 the graph algorithms (like ShortestPath) have visited and output it with
 the
 result of the query? I would like to do that to analyze the performance and
 load of query processing. Any ideas?

 Thanks!

 Stephan
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 User@lists.neo4j.org
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-- 
Tobias Ivarsson tobias.ivars...@neotechnology.com
Hacker, Neo Technology
www.neotechnology.com
Cellphone: +46 706 534857
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