I'm researching Neo4j to compare it's performance for implementing an access control list. It seems like this is a great fit.
Here's an article from a few years ago describing this exact use case.
http://blog.neo4j.org/2010/02/access-control-lists-graph-database-way.html.
The has_access method though is written in ruby. I would think that using gremlin to process the query on the server would be more efficient for large graphs. How would I determine if a user has access to a node using Gremlin?
Thanks!
It turns out that for this problem, access to a folder can be determined by parsing the shortest paths between the user and the user and the folder.
Here is a cypher query that returns the shortest paths between two nodes, where the user is at node 157 and the folder is at node 160.
START u=node(157),f=node(160)
MATCH p=allShortestPaths(u-[*]->f)
RETURN p
Related
I am yet trying to make use of neo4j to perform a complex query (similar to shortest path search except I have very strange conditions applied to this search like minimum path length in terms of nodes traversed count).
My dataset contains around 2.5M nodes of one single type and around 1.5 billion edges (One single type as well). Each given node has on average 1000 directional relation to a "next" node.
Yet, I have a query that allows me to retrieve this shortest path given all of my conditions but the only way I found to have decent response time (under one second) is to actually limit the number of results after each new node added to the path, filter it, order it and then pursue to the next node (This is kind of a greedy algorithm I suppose).
I'd like to limit them a lot less than I do in order to yield more path as a result, but the problem is the exponential complexity of this search that makes going from LIMIT 40 to LIMIT 60 usually a matter of x10 ~ x100 processing time.
This being said, I am yet evaluating several solutions to increase the speed of the request but I'm quite unsure of the result they will yield as I'm not sure about how neo4j really stores my data internally.
The solution I think about yet is to actually add a property to my relationships which would be an integer in between 1 and 15 because I usually will only query the relationships that have one or two max different values for this property. (like only relationships that have this property to 8 or 9 for example).
As I can guess yet, for each relationship, neo4j then have to gather the original node properties and use it to apply my further filters which takes a very long time when crossing 4 nodes long path with 1000 relationships each (I guess O(1000^4)). Am I right ?
With relationship properties, will it have direct access to it without further data fetching ? Is there any chance it will make my queries faster? How are neo4j edges properties stored ?
UPDATE
Following #logisima 's advice I've written a procedure directly with the Java traversal API of neo4j. I then switched to the raw Java procedure API of Neo4J to leverage even more power and flexibility as my use case required it.
The results are really good : the lower bound complexity is overall a little less thant it was before but the higher bound is like ten time faster and when at least some of the nodes that will be used for the traversal are in the cache of Neo4j, the performances just becomes astonishing (depth 20 in less than a second for one of my tests when I only need depth 4 usually).
But that's not all. The procedures makes it very very easily customisable while keeping the performances at their best and optimizing every single operation at its best. The results is that I can use far more powerful filters in far less computing time and can easily update my procedure to add new features. Last but not least Procedures are very easily pluggable with spring-data for neo4j (which I use to connect neo4j to my HTTP API). Where as with cypher, I would have to auto generate the queries (as being very complex, there was like 30 java classes to do the trick properly) and I should have used jdbc for neo4j while handling a separate connection pool only for this request. Cannot recommend more to use the awesome neo4j java API.
Thanks again #logisima
If you're trying to do a custom shortespath algo, then you should write a cypher procedure with the traversal API.
The principe of Cypher is to make pattern matching, and you want to traverse the graph in a specific way to find your good solution.
The response time should be really faster for your use-case !
I'm struggling for days to find a way for finding all paths (to a maximum length) between two nodes while controlling the path exploration by Neo4j by sorting the relationships that are going to be explored (by one of their properties).
So to be clear, lets say I want to find K best paths between two nodes until a maximum length M. The query will be like:
match (source{name:"source"}), (target{name:"target"}),
p = (source)-[*..M]->(target)
return p order by length(p) limit K;
So far so good. But lets say the relationships of the path have a property called "priority". What I want is to write a query that tells Neo4j on each step of path exploration which relationships should be explored first.
I know that can be possible when I use the java libraries and an embedded database (By implementing PathExpander interface and giving it as input to the GraphAlgoFactory.allSimplePaths() function in Java).
But now I'm trying to find a way doing this in a server mode database access using Bolt or REST api.
Is there any way to do this in the server mode? Or maybe using Java libraries functions while accessing the graph in server mode?
use labels and an index to find your two start-nodes
perhaps consider allShortestPaths to make it faster
try this:
match (source{name:"source"}), (target{name:"target"}),
p = (source)-[rels:*..20]->(target)
return p, reduce(prio=0, r IN rels | prio + r.priority) as priority
order by priority ASC, length(p)
limit 100;
I had a very similar problem. I was trying to find the shortest path from one node to all other nodes. I had written a query similar to the one in the answer above (https://stackoverflow.com/a/38030536/783836) and couldn't get it to perform in any reasonable time.
Asking Can Graph DBs perform well with unspecified end nodes? pointed me to the solution: the Single Shortest Path algorithm.
In Neo4j you need to install the Graph Data Science Library and make use of this function: gds.alpha.shortestPath.deltaStepping.stream
I've got my graph database, populated with nodes, relationships, properties etc. I'd like to see an overview of how the whole database is connected, each relationship to each node, properties of a node etc.
I don't mean view each individual node, but rather something like an ERD from a relational database, something like this, with the node labels. Is this possible?
You can use the metadata by running the command call db.schema().
In Neo4j v4 call db.schema() is deprecated, you can now use call db.schema.visualization()
As far as I know, there is no straight-forward way to get a nicely pictured diagram of a neo4j database structure.
There is a pre-defined query in the neo4j browser which finds all node types and their relationships. However, it traverses the complete graph and may fail due to memory errors if you have to much data.
Also, there is neoprofiler. It's a tool which claims to so what you ask. I never tried and it didn't get too many updates lately. Still worth a try: https://github.com/moxious/neoprofiler
Even though this is not a graphical representation, this query will give you an idea on what type of nodes are connected to other nodes with what type of relationship.
MATCH (n)
OPTIONAL MATCH (n)-[r]->(x)
WITH DISTINCT {l1: labels(n), r: type(r), l2: labels(x)}
AS `first degree connection`
RETURN `first degree connection`;
You could use this query to then unwind the labels to write that next cypher query dynamically (via a scripting language and using the REST API) and then paste that query back into the neo4j browser to get an example set of the data.
But this should be good enough to get an overview of your graph. Expand from here.
TL,DR: I need a query which gives me all nodes/relationships which contain a certain value (in my case a string, so much I know), without knowing which property(key) contains the string. I am using neo4j(latest version), meteor (latest version) and the meteor neo4j driver, which is recommended on the neo4j website for meteor.
Currently I am working (as part of my bachelor thesis) on a tool to visualize the output of any Cypher query on any database, regardless of the database contents.
So far I've managed to correctly display nodes/relationships which are coming out. My problem now is to visualize (get nodes and relationships to feed into my frontend) textual queries like (taken from the neo4j movie database, which I am using for development)
MATCH (tom:Person {name:"Tom Hanks"})-[:ACTED_IN]->(m)<-[:ACTED_IN]-(coActors)
RETURN coActors.name
This kind of queries only returns an array of strings and not whole nodes or relationships. I now need some way (preferably a Cypher query) to get all nodes which contain for example the string "Audrey Tatou".
The problem I've now run into is that I didn't find a way to write a query which doesn't need something like
MATCH n
WHERE Person.name = "some name"
Since I don't know anything about the contents of the database I cannot use
WHERE propertyName = "propertyValue"
since I only know the value but not the name of the property.
The only solution here will be to get every nodes with your label and check properties and values using reflection on client side.
Using cypher, the solution would be to get all properties and their values and parse their values using a foreach loop. Maybe you can do this, but I'm really not sure, it's a recent feature but you can still give a try.
Here is what I found for the cypher solution: How can I return all properties for a node using Cypher?
So, you have query that returns array of string.
In fact - you can receive almost anything as result. Cypher is capable to return just bare strings, that are not related to anything.
Long story short - you can't vizualize this data, because of this data nature. Best you can do is to represent them as table (or similar), like Neo4j browser do this.
But, there is (probably) solution for you. Neo4j has feature called Legacy indexing. And there you can find full text indexes. Maybe this can help you.
You can just use a driver that returns nodes and rels, or if you do the queries manually add resultDataContents entry
{statements:[{statement:"MATCH ..","resultDataContents",["graph"]}]}
to your payload and you get nodes and relationships back.
I'm toying around with Neo4J. My Data consists of users who own objects which are tagged by tags. There my schema looks like:
(:User)-[:OWNS]->(:Object)-[:TAGGED_AS]->(:Tag)
I have written a script that generates me a sample Graph. Currently I have 100 User, ~2500 Tag and ~10k Object nodes in the database. Between those I have ~700k relationships. I know want to find every Object that is not owned by a certain User but related over a Tag the User has used himself. There query looks like:
MATCH (user:User {username: 'Cristal'})
WITH user
MATCH (user)-[:OWNS]->(obj:Object)-[:TAGGED_AS]->(tag:Tag)<-[:TAGGED_AS]-(other:Object)
WHERE NOT (user)-[:OWNS]->(other)
RETURN other
LIMIT 20
However, this query runs ~1-5 minutes (depending on the user and how many objects he owns), which is a not only a bit to slow. What am I doing wrong? I consider this a rather "trivial" query against a graph of modest size. I'm using Neo4J 2.1.6 Community and already set the Java Heap to 2000 MB (and I can see that there is a Java process using this much). Am I missing an index or something like that (I'm new to Neo4J)?
I honestly expected the result to be pretty much instant especially considering that the Neo4J docs mention the I should use a heap between 1 and 4 GB for 100 million objects...and I'm only close to a 1/100 of this number.
If it is my Query (which I hope and expect) how can I improve it? What is something you have to be aware when writing queries?
Do you have an index on the username property?
CREATE INDEX ON :User(username)
Also you don't really need that WITH there, so maybe drop it to see if it helps:
MATCH (user:User {username: 'Cristal'})-[:OWNS]->(obj:Object)-[:TAGGED_AS]->(tag:Tag)<-[:TAGGED_AS]-(other:Object)
WHERE NOT (user)-[:OWNS]->(other)
RETURN other
LIMIT 20
Also, I don't think it will make a different, but you can drop the obj and tag variables since you're not using them elsewhere in the query.
Also, if you're generating sample graphs you may want to check out GraphGen:
http://graphgen.neoxygen.io/