neo4j优化读取查询性能

Question

在优化读取查询时，我需要帮助，当活动用户在250左右运行时，它变得非常慢(大约3秒)，并且负载较少，只需几毫秒。我们的图形大小为435 MB，我们正在一个16 GB内存的neo4j 3.5集群上运行它。

查询：

MATCH (lesson:Mlo)-[MLO_TO_CONTENT]->(Content)-[CONTENT_TO_SKILL]->(skill:Skill)<-[OUTCOME_TO_SKILL]-(outcome:Outcome)
WHERE lesson.mloUuid IN ["uuid-1", "uuid-2"]
AND outcome.boardId = lesson.boardId
AND outcome.gradeId = lesson.gradeId
AND outcome.subjectId = lesson.subjectId
AND exists(skill.name)
AND exists(skill.uuid)
AND exists(outcome.outcomeKey)
RETURN lesson.mloUuid as lessonUuid, skill.name as skillName, skill.uuid as skillUuid, collect(distinct outcome.outcomeKey) as outcomes

图：

Heap 6144 MB
Page Cache 5293 MB

*sysinfo

Page Cache
Faults    7348
Evictions    0
File Mappings    2544
Bytes Read    58851674
Flushes    9140
Eviction Exceptions    0
File Unmappings    2516
Bytes Written    280641246
Hit Ratio    100.00%
Usage Ratio    1.10%

配置文件：

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Answer 1

您可以尝试对此进行分析：

MATCH (lesson:Mlo)-[MLO_TO_CONTENT]->(content)-[CONTENT_TO_SKILL]->(skill)<-[OUTCOME_TO_SKILL]-(outcome)
WHERE lesson.mloUuid IN ["uuid-1", "uuid-2"]
AND skill.name IS NOT NULL
AND skill.uuid IS NOT NULL
AND outcome.outcomeKey IS NOT NULL
AND outcome.boardId = lesson.boardId
AND outcome.gradeId = lesson.gradeId
AND outcome.subjectId = lesson.subjectId
RETURN lesson.mloUuid as lessonUuid, skill.name as skillName, skill.uuid as skillUuid, collect(distinct outcome.outcomeKey) as outcomes

在这个查询中，我们删除了skill和outcome节点的标签匹配。在配置图中，他们的点击量约为5万次。但是，如果响应中存在某些不匹配，则应该重新添加它们。另外，我们已经用exists()更新了IS NOT NULL检查，以便使用更多的索引。您可以阅读更多关于它的这里。

另一个可能的选择是在查询中提供JOIN提示。这些提示基本上告诉查询规划者如何针对某些特定节点遍历路径，从而将遍历成本降到最低。尝试下面的查询，我们已经使用子句USING JOIN ON提供了提示，任何节点都可以跟随子句，我使用了skill节点，但是您也可以使用lesson、content或outcome，并比较查询响应时间。

PROFILE MATCH (lesson:Mlo)-[MLO_TO_CONTENT]->(content)-[CONTENT_TO_SKILL]->(skill:Skill)<-[OUTCOME_TO_SKILL]-(outcome:Outcome)
USING JOIN ON skill
WHERE lesson.mloUuid IN ["uuid-1", "uuid-2"]
AND outcome.boardId = lesson.boardId
AND outcome.gradeId = lesson.gradeId
AND outcome.subjectId = lesson.subjectId
AND skill.name IS NOT NULL
AND skill.uuid IS NOT NULL
AND outcome.outcomeKey IS NOT NULL
RETURN lesson.mloUuid as lessonUuid, skill.name as skillName, skill.uuid as skillUuid, collect(distinct outcome.outcomeKey) as outcomes

您可以阅读更多关于规划师提示这里的信息。