Delete all nodes and relationships

[Johnny Weng Luu]

First of all, thank you so much for introducing mutative Cypher. It totally rocks!!! :D

I usually delete all nodes and relationships with two queries:

All nodes with relationships:

      START n = node(*)

      MATCH n-[r]-()

      DELETE n, r

All nodes without relationships:

      START n = node(*)

      DELETE n

Is there a way to delete all nodes and relationships with just one query?

I thought this one would do it but it failed:

      START n = node(*)

      MATCH n-[r?]-()

      DELETE n, r

Johnny

[Michael Hunger]

How did it fail?

It shouldn't at least not in 1.8-SNAPSHOT ?

Michael

[Johnny Weng Luu]

It doesn't delete anything and it messes up the db so I can't delete any node afterwards.

I'm using the latest 1.8 Heroku add-on.

Johnny

[Johnny Weng Luu]

Perhaps the problem is that when "r" is not available but yet I have "r" in DELETE?

Johnny

[Michael Hunger]

You mean it messes up the console?

Heroku uses 1.8.M02 imho.


Does it work for you here http://console.neo4j.org ?

Oh, you might want to exclude the root node (with where ID(n) <> 0)

Michael

[Johnny Luu]

Why <> 0? Is it possible for an ID to be less than 0?

Johnny

Sent from my iPad

[Peter Neubauer]

No,
It's just that "! =" is already claimed for optional properties...

Send from mobile.

[Yabo Gao]

I tried this and it went ok:

START n = node(*)

      MATCH n-[r]-()

      DELETE n, r

 DELETE n

Its really similar to yours.

[Michael Hunger]

With a reasonable heap size (4-8G) you can delete up to 1M records (nodes and rels in one run)

If you want to delete all I very much recommend to just to delete the data/graph.db directory.

if you have more data to delete out of even more data, you can do something like this:

// find the nodes you want to delete

MATCH (n:Foo) where n.foo = "bar" 

// take the first 10k nodes and their rels (if more than 100 rels / node on average lower this number)

WITH n LIMIT 10000

MATCH (n)-[r]-()

DELETE n,r

RETURN count(*);

run it until the statement returns 0 (zero).

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[neo4jnovice]

How can you ensure that you have successfully updated the heap size to 4-8 GB? I updated it on my Java Runtime Environment Settings and also in the neo4j-wrapper.conf file. However, possibly due to my changing internet speed at the apartment, there is no change in speed after I increased the heap size. Also, the metric system claims that 1 GB is 1000 MB. However, in class, we learned that 1 GB is 2^10=1024 MB. Which metric system is preferred in this case?