Question

Neo4j版本2.2.4

我使用LOAD CSV导入大量节点和关系。我使用MERGE来获取或创建节点。为了性能，我还为节点属性创建了一个唯一索引。

CREATE CONSTRAINT ON (e:RESSOURCE) assert e.url is unique;

USING PERIODIC COMMIT 10000
LOAD CSV FROM 'file:///Users/x/data.csv' AS line FIELDTERMINATOR '\t'
MERGE (subject:RESSOURCE {url: trim(line[0])})
MERGE (object:RESSOURCE {url: trim(line[1])})
CREATE (subject)-[:EQUIVALENCE]->(object);

问题是导入约1Mio。边缘表现非常糟糕。我分析了导入和单个MERGE查询，我看不到任何使用唯一索引。相反，MATCH查询使用索引。如何将MERGE与索引一起使用？

Answer 1

彼得是正确的，有更多解释：

您遇到了EAGER问题，请参阅：http://www.markhneedham.com/blog/2014/10/23/neo4j-cypher-avoiding-the-eager/您应该在EXPLAIN输出中看到它（删除定期提交并使用说明）

+--------------+----------------------------------+-----------------------+
| Operator     | Identifiers                      | Other                 |
+--------------+----------------------------------+-----------------------+
| +EmptyResult |                                  |                       |
| |            +----------------------------------+-----------------------+
| +UpdateGraph | anon[179], line, object, subject | CreateRelationship    |
| |            +----------------------------------+-----------------------+
| +UpdateGraph | line, object, subject            | MergeNode; :RESSOURCE |
| |            +----------------------------------+-----------------------+
| +Eager       | line, subject                    |                       |
| |            +----------------------------------+-----------------------+
| +UpdateGraph | line, subject                    | MergeNode; :RESSOURCE |
| |            +----------------------------------+-----------------------+
| +LoadCSV     | line                             |                       |
+--------------+----------------------------------+-----------------------+

Eager将提取您的整个CSV文件以确保隔离并有效地禁用您的定期提交。

如果你进行两次传球，你也可以尝试：

CREATE CONSTRAINT ON (e:RESSOURCE) assert e.url is unique;

USING PERIODIC COMMIT 10000
LOAD CSV FROM 'file:///Users/x/data.csv' AS line FIELDTERMINATOR '\t'
FOREACH (url in line[0..1] |
   MERGE (subject:RESSOURCE {url: trim(url)})
);

USING PERIODIC COMMIT 10000
LOAD CSV FROM 'file:///Users/x/data.csv' AS line FIELDTERMINATOR '\t'
MATCH (subject:RESSOURCE {url: trim(line[0])})
MATCH (object:RESSOURCE {url: trim(line[1])})
CREATE (subject)-[:EQUIVALENCE]->(object);

Answer 2

试试这个：

MATCH (subject:RESSOURCE {url: trim(line[0])}), (object:RESSOURCE {url: trim(line[1])}) 
MERGE (subject)-[:EQUIVALENCE]->(object)

修改我看到你也想合并节点 - 我建议为每个节点做一个MERGE：

MERGE (subject:RESSOURCE {url: trim(line[0])})

我还建议您在构建csv文件时进行修剪，以便限制neo4j执行此操作的次数并简化此密码。

编辑2 （感谢Kai更正我上述MERGE声明的评论）：

如果您想使用更多属性执行更复杂的MERGE，您可以执行此操作：

MERGE (subject:RESSOURCE {url: trim(line[0])}) ON CREATE SET source=trim(line[1]) ON MERGE SET source=trim(line[1])

Neo4j Merge不使用唯一约束索引

2 个答案: