Neo4j Merge不使用唯一约束索引

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.如何在索引中使用MERGE？

Answer 1

彼得是正确的,还有一些解释:

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.

如果你做两次通过,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);