问题描述
通过Cypher从所有节点和关系中清除图形的最佳方法是什么?
What is the best way to cleanup the graph from all nodes and relationships via Cypher?
在 http://neo4j.com/docs/stable/query-delete.html#delete-delete-a-node-and-connected-relationships 示例
MATCH (n)
OPTIONAL MATCH (n)-[r]-()
DELETE n,r
有注释:
那么，下面的方法更好吗?
So, is the following better?
MATCH ()-[r]-() DELETE r
和
MATCH (n) DELETE n
或者还有另一种对大型图形更好的方法吗?
Or is there another way that is better for large graphs?
推荐答案
正如您提到的，最简单的方法是停止Neo4j，删除data/graph.db文件夹并重新启动它.
As you've mentioned the most easy way is to stop Neo4j, drop the data/graph.db folder and restart it.
通过Cypher删除大图总是比较慢，但是如果您使用适当的事务大小来防止内存问题(记住事务在提交之前先在内存中建立)，仍然可以实现.通常，50-100k原子操作是个好主意.您可以在删除语句中添加一个限制，以控制tx的大小，并报告已删除的节点数.重新运行此语句，直到返回值0:
Deleting a large graph via Cypher will be always slower but still doable if you use a proper transaction size to prevent memory issues (remember transaction are built up in memory first before they get committed). Typically 50-100k atomic operations is a good idea. You can add a limit to your deletion statement to control tx sizes and report back how many nodes have been deleted. Rerun this statement until a value of 0 is returned back:
MATCH (n)
OPTIONAL MATCH (n)-[r]-()
WITH n,r LIMIT 50000
DELETE n,r
RETURN count(n) as deletedNodesCount
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