那些遇到过的问题

Neo4j:标签与索引属性？

Ase*_*ore 21 neo4j cypher

假设你是Twitter,并且:

  • 你有(:User)和(:Tweet)节点;
  • 推文可以被标记; 和
  • 您想查询当前正在等待审核的已标记推文列表.

您可以为这些推文添加标签,例如:AwaitingModeration,添加和索引属性,例如isAwaitingModeration = true|false.

一种选择本质上比另一种更好吗？

我知道最好的答案可能是尝试加载测试两个:),但Neo4j的实现POV有什么能使一个选项更健壮或适合这种查询吗？

这取决于任何特定时刻这种状态的推文数量吗？如果它在10s与1000s之间,那会有所作为吗？

我的印象是标签更适合大量节点,而索引属性对于较小的卷(理想情况下,唯一节点)更好,但我不确定这是否真的如此.

谢谢!

Chr*_*sen 34

更新:跟进发布的博客文章.

当我们为客户建模数据集和Active/NonActive实体的典型用例时,这是一个常见问题.

这是关于我对Neo4j2.1.6有效的一点反馈:

要点1.在标签上或索引属性上匹配之间的数据库访问不会有差异并返回节点

点2.例如,当这样的节点位于模式的末尾时将遇到差异

MATCH (n:User {id:1})
WITH n
MATCH (n)-[:WRITTEN]->(post:Post)
WHERE post.published = true
RETURN n, collect(post) as posts;
Run Code Online (Sandbox Code Playgroud)

- 

PROFILE MATCH (n:User) WHERE n._id = 'c084e0ca-22b6-35f8-a786-c07891f108fc'
> WITH n
> MATCH (n)-[:WRITTEN]->(post:BlogPost)
> WHERE post.active = true
> RETURN n, size(collect(post)) as posts;
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| n                                                                                                                                                         | posts |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Node[118]{_id:"c084e0ca-22b6-35f8-a786-c07891f108fc",login:"joy.wiza",password:"7425b990a544ae26ea764a4473c1863253240128",email:"hayes.shaina@yahoo.com"} | 1     |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row

ColumnFilter(0)
  |
  +Extract
    |
    +ColumnFilter(1)
      |
      +EagerAggregation
        |
        +Filter
          |
          +SimplePatternMatcher
            |
            +SchemaIndex

+----------------------+------+--------+----------------------+----------------------------------------------------------------------------+
|             Operator | Rows | DbHits |          Identifiers |                                                                      Other |
+----------------------+------+--------+----------------------+----------------------------------------------------------------------------+
|      ColumnFilter(0) |    1 |      0 |                      |                                                      keep columns n, posts |
|              Extract |    1 |      0 |                      |                                                                      posts |
|      ColumnFilter(1) |    1 |      0 |                      |                                           keep columns n,   AGGREGATION153 |
|     EagerAggregation |    1 |      0 |                      |                                                                          n |
|               Filter |    1 |      3 |                      | (hasLabel(post:BlogPost(1)) AND Property(post,active(8)) == {  AUTOBOOL1}) |
| SimplePatternMatcher |    1 |     12 | n, post,   UNNAMED84 |                                                                            |
|          SchemaIndex |    1 |      2 |                 n, n |                                                {  AUTOSTRING0}; :User(_id) |
+----------------------+------+--------+----------------------+----------------------------------------------------------------------------+

Total database accesses: 17
Run Code Online (Sandbox Code Playgroud)

在这种情况下,Cypher将不会使用该索引:Post(published).

因此,如果您拥有ActivePost标签,则标签的使用会更加高效:

neo4j-sh (?)$ PROFILE MATCH (n:User) WHERE n._id = 'c084e0ca-22b6-35f8-a786-c07891f108fc'
> WITH n
> MATCH (n)-[:WRITTEN]->(post:ActivePost)
> RETURN n, size(collect(post)) as posts;
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| n                                                                                                                                                         | posts |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Node[118]{_id:"c084e0ca-22b6-35f8-a786-c07891f108fc",login:"joy.wiza",password:"7425b990a544ae26ea764a4473c1863253240128",email:"hayes.shaina@yahoo.com"} | 1     |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row

ColumnFilter(0)
  |
  +Extract
    |
    +ColumnFilter(1)
      |
      +EagerAggregation
        |
        +Filter
          |
          +SimplePatternMatcher
            |
            +SchemaIndex

+----------------------+------+--------+----------------------+----------------------------------+
|             Operator | Rows | DbHits |          Identifiers |                            Other |
+----------------------+------+--------+----------------------+----------------------------------+
|      ColumnFilter(0) |    1 |      0 |                      |            keep columns n, posts |
|              Extract |    1 |      0 |                      |                            posts |
|      ColumnFilter(1) |    1 |      0 |                      | keep columns n,   AGGREGATION130 |
|     EagerAggregation |    1 |      0 |                      |                                n |
|               Filter |    1 |      1 |                      |     hasLabel(post:ActivePost(2)) |
| SimplePatternMatcher |    1 |      4 | n, post,   UNNAMED84 |                                  |
|          SchemaIndex |    1 |      2 |                 n, n |      {  AUTOSTRING0}; :User(_id) |
+----------------------+------+--------+----------------------+----------------------------------+

Total database accesses: 7
Run Code Online (Sandbox Code Playgroud)

要点3.始终使用标签作为正面,对于上述情况,具有草稿标签将强制您执行以下查询:

MATCH (n:User {id:1})
WITH n
MATCH (n)-[:POST]->(post:Post)
WHERE NOT post :Draft
RETURN n, collect(post) as posts;
Run Code Online (Sandbox Code Playgroud)

这意味着Cypher将打开每个节点标签标头并对其进行过滤.

要点4.避免在多个标签上匹配

MATCH (n:User {id:1})
WITH n
MATCH (n)-[:POST]->(post:Post:ActivePost)
RETURN n, collect(post) as posts;

neo4j-sh (?)$ PROFILE MATCH (n:User) WHERE n._id = 'c084e0ca-22b6-35f8-a786-c07891f108fc'
> WITH n
> MATCH (n)-[:WRITTEN]->(post:BlogPost:ActivePost)
> RETURN n, size(collect(post)) as posts;
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| n                                                                                                                                                         | posts |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Node[118]{_id:"c084e0ca-22b6-35f8-a786-c07891f108fc",login:"joy.wiza",password:"7425b990a544ae26ea764a4473c1863253240128",email:"hayes.shaina@yahoo.com"} | 1     |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row

ColumnFilter(0)
  |
  +Extract
    |
    +ColumnFilter(1)
      |
      +EagerAggregation
        |
        +Filter
          |
          +SimplePatternMatcher
            |
            +SchemaIndex

+----------------------+------+--------+----------------------+---------------------------------------------------------------+
|             Operator | Rows | DbHits |          Identifiers |                                                         Other |
+----------------------+------+--------+----------------------+---------------------------------------------------------------+
|      ColumnFilter(0) |    1 |      0 |                      |                                         keep columns n, posts |
|              Extract |    1 |      0 |                      |                                                         posts |
|      ColumnFilter(1) |    1 |      0 |                      |                              keep columns n,   AGGREGATION139 |
|     EagerAggregation |    1 |      0 |                      |                                                             n |
|               Filter |    1 |      2 |                      | (hasLabel(post:BlogPost(1)) AND hasLabel(post:ActivePost(2))) |
| SimplePatternMatcher |    1 |      8 | n, post,   UNNAMED84 |                                                               |
|          SchemaIndex |    1 |      2 |                 n, n |                                   {  AUTOSTRING0}; :User(_id) |
+----------------------+------+--------+----------------------+---------------------------------------------------------------+

Total database accesses: 12
Run Code Online (Sandbox Code Playgroud)

这将导致Cypher在第3点采用相同的流程.

要点5.如果可能,请避免需要通过良好类型的命名关系匹配标签

MATCH (n:User {id:1})
WITH n
MATCH (n)-[:PUBLISHED]->(p)
RETURN n, collect(p) as posts
Run Code Online (Sandbox Code Playgroud)

- 

MATCH (n:User {id:1})
WITH n
MATCH (n)-[:DRAFTED]->(post)
RETURN n, collect(post) as posts;

neo4j-sh (?)$ PROFILE MATCH (n:User) WHERE n._id = 'c084e0ca-22b6-35f8-a786-c07891f108fc'
> WITH n
> MATCH (n)-[:DRAFTED]->(post)
> RETURN n, size(collect(post)) as posts;
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| n                                                                                                                                                         | posts |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Node[118]{_id:"c084e0ca-22b6-35f8-a786-c07891f108fc",login:"joy.wiza",password:"7425b990a544ae26ea764a4473c1863253240128",email:"hayes.shaina@yahoo.com"} | 3     |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row

ColumnFilter(0)
  |
  +Extract
    |
    +ColumnFilter(1)
      |
      +EagerAggregation
        |
        +SimplePatternMatcher
          |
          +SchemaIndex

+----------------------+------+--------+----------------------+----------------------------------+
|             Operator | Rows | DbHits |          Identifiers |                            Other |
+----------------------+------+--------+----------------------+----------------------------------+
|      ColumnFilter(0) |    1 |      0 |                      |            keep columns n, posts |
|              Extract |    1 |      0 |                      |                            posts |
|      ColumnFilter(1) |    1 |      0 |                      | keep columns n,   AGGREGATION119 |
|     EagerAggregation |    1 |      0 |                      |                                n |
| SimplePatternMatcher |    3 |      0 | n, post,   UNNAMED84 |                                  |
|          SchemaIndex |    1 |      2 |                 n, n |      {  AUTOSTRING0}; :User(_id) |
+----------------------+------+--------+----------------------+----------------------------------+

Total database accesses: 2
Run Code Online (Sandbox Code Playgroud)

性能更高,因为它将使用图的所有功能,只需遵循节点的关系,导致不再访问数据库,而不是匹配用户节点,因此不会对标签进行过滤.

这是我的0,02欧元

  • 优秀的答案,全面的.我学到了很多东西,我喜欢学习东西.在我看来,良好的neo4j建模策略的一些原则仍在不断发展.如果社区可以在文档中收集更多这些建模原则,那将是一件好事,因为许多新用户都是图形新手. (5认同)
  • 同意,谢谢你的全面答复.我有一些后续问题; 太糟糕了这个小评论框是唯一的地方.第2点:我不相信标签使*遍历*更快.只有关系类型才对,对吧？第4点:为什么指定更多标签会更慢？Cypher不够聪明,不能先使用基数较低的那个吗？一般来说,坚持原始q中的示例可能会很好:*只是*全局查找,*不是*来自例如用户节点的遍历.所以我认为我对这种情况的看法是:两种选择都是等价的？ (2认同)

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