我正在尝试neo4j进行我的成绩项目，因此我决定使用LDBC提供的数据源创建一个数据库。 these queries附带了此数据源。
因此，我决定运行那些查询之一并收集其执行时间（我使用cypher-shell命令运行了它们）。所以我收集了这些时间：
553575, 558724, 556443, 556675, 551304, 555385, 552896
注意：我参加了第一次比赛，因为如post所述，由于冷缓存，第一次似乎是高峰。
一切都很顺利，然后，我决定用新标签创建一些路径，使数据库从1.5GB增长到2.4GB。我决定再次运行期望它们变慢的查询。令我惊讶的是，我看到时间大大缩短了。
382331, 380566, 405636, 405953, 407277, 391804, 371134, ....
从此post开始。我希望它们能像在同一时间（如第一次运行）一样，并且可能更大，但绝对不会更小。
出于这个问题的目的，我使用的是 AWS计算机，特别是 i3.4xlarge 实例（16个vCPU，122GB RAM和2x 1.9TB NVMe SSD） 。我正在使用Neo4j的当前版本是 3.3.5 ，如上所述，我正在使用cypher-shell。
此外，我没有在此计算机上运行其他程序/进程，因此我认为我们可以消除该问题（尽管如此，它应该使它们变慢而不是加快速度）。
谢谢，我只是想问一下是否有人可以在这个问题上给我一些启发：）
编辑：
我所做的更改在：Message节点和：Person的路径之间添加了一些路径。在：Person和：Person之间也有一些，在：TagClass（其他标签）和：Person之间有一些。此外，数据库在：Tag（name）、: Person（name）、: TagClass（name）和：Country（name）上都有索引，但是出于执行查询的目的，删除了这些索引。
原始查询：
PROFILE
MATCH (tag:Tag {name: 'Arnold_Schwarzenegger'})
MATCH (tag)<-[:HAS_TAG]-(message1:Message)-[:HAS_CREATOR]->(person1:Person)
MATCH (tag)<-[:HAS_TAG]-(message2:Message)-[:HAS_CREATOR]->(person1)
OPTIONAL MATCH (message2)<-[:LIKES]-(person2:Person)
OPTIONAL MATCH (person2)<-[:HAS_CREATOR]-(message3:Message)<-[like:LIKES]-(p3:Person)
RETURN
person1.id,
count(DISTINCT like) AS authorityScore
ORDER BY
authorityScore DESC,
person1.id ASC
LIMIT 100
这些是两次运行的配置文件，原因是空间仅添加了一个计划。我可以向您保证，它们都是完全相同的（即使在数据库命中，扩展路径上，等等）：
第一次运行：
| Plan | Statement | Version | Planner | Runtime | Time | DbHits | Rows |
| "PROFILE" | "READ_ONLY" | "CYPHER 3.3" | "COST" | "INTERPRETED" | 556443 | 0 | 100 |
第二：
| Plan | Statement | Version | Planner | Runtime | Time | DbHits | Rows |
| "PROFILE" | "READ_ONLY" | "CYPHER 3.3" | "COST" | "INTERPRETED" | 371134 | 0 | 100 |
计划：
+----------------------+----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| Operator | Estimated Rows | Rows | DB Hits | Cache H/M | Identifiers | Other |
+----------------------+----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +ProduceResults | 100 | 100 | 0 | 0/0 | anon[349], anon[355], authorityScore, person1.id | 0.0 |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Projection | 100 | 100 | 0 | 0/0 | anon[349], anon[355], authorityScore, person1.id | 0.0; {person1.id : , authorityScore : } |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Top | 100 | 100 | 0 | 0/0 | anon[349], anon[355] | 0.0; 100; anon[355], anon[349] |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +EagerAggregation | 126593 | 1842 | 49948155 | 0/0 | anon[349], anon[355] | 0.0; anon[349] |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Apply | 16025884097 | 49948155 | 0 | 0/0 | person2, anon[219], message3, anon[60], tag, anon[136], p3, message1, anon[167], anon[271], message2, anon[91], person1, like | 0.0 |
| |\ +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Optional | 7317 | 49948155 | 0 | 0/0 | person2, message3, p3, anon[271], like | 0.0 |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Filter | 5037 | 49897917 | 49897917 | 0/0 | person2, message3, p3, anon[271], like | 0.0; p3:Person |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Expand(All) | 5037 | 49897917 | 108680609 | 0/0 | person2, message3, p3, anon[271], like | 0.0; (message3)<-[like:LIKES]-(p3) |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Filter | 7028 | 58782692 | 58782692 | 0/0 | anon[271], message3, person2 | 0.0; message3:Message |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Expand(All) | 7028 | 58782692 | 58866898 | 0/0 | anon[271], message3, person2 | 0.0; (person2)<-[anon[271]:HAS_CREATOR]-(message3) |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Argument | 7317 | 130898 | 0 | 0/0 | person2 | 0.0 |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +OptionalExpand(All) | 7317 | 130898 | 220191 | 0/0 | person2, anon[219], anon[60], tag, anon[136], message1, anon[167], message2, anon[91], person1 | 0.0; (message2)<-[anon[219]:LIKES]-(person2); person2:Person |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +NodeHashJoin | 7317 | 51779 | 0 | 0/0 | anon[60], tag, anon[136], message1, anon[167], message2, anon[91], person1 | 0.0; tag, person1 |
| |\ +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Filter | 341165 | 4241 | 4241 | 0/0 | tag, anon[136], anon[167], message2, person1 | 0.0; person1:Person |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Expand(All) | 341165 | 4241 | 8482 | 0/0 | tag, anon[136], anon[167], message2, person1 | 0.0; (message2)-[anon[167]:HAS_CREATOR]->(person1) |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Filter | 341165 | 4241 | 4646 | 0/0 | anon[136], message2, tag | 0.0; message2:Message |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Expand(All) | 372142 | 4646 | 4647 | 0/0 | anon[136], message2, tag | 0.0; (tag)<-[anon[136]:HAS_TAG]-(message2) |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Filter | 1608 | 1 | 16080 | 0/0 | tag | 0.0; tag.name = { AUTOSTRING0} |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +NodeByLabelScan | 16080 | 16080 | 16081 | 0/0 | tag | 0.0; :Tag |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Filter | 341165 | 4241 | 4241 | 0/0 | anon[60], tag, message1, anon[91], person1 | 0.0; person1:Person |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Expand(All) | 341165 | 4241 | 8482 | 0/0 | anon[60], tag, message1, anon[91], person1 | 0.0; (message1)-[anon[91]:HAS_CREATOR]->(person1) |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Filter | 341165 | 4241 | 4646 | 0/0 | anon[60], message1, tag | 0.0; message1:Message |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Expand(All) | 372142 | 4646 | 4647 | 0/0 | anon[60], message1, tag | 0.0; (tag)<-[anon[60]:HAS_TAG]-(message1) |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Filter | 1608 | 1 | 16080 | 0/0 | tag | 0.0; tag.name = { AUTOSTRING0} |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +NodeByLabelScan | 16080 | 16080 | 16081 | 0/0 | tag | 0.0; :Tag |
+----------------------+----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+------------------------------ --------------------------------+
... Results ...
100 rows available after 371134 ms, consumed after another 0 ms
注意： SO不允许我写超过30000个字符，因此必须减少文本。
答案 0 :(得分：0)
Cypher计划器在决定如何执行查询时会考虑数据库的当前特征。对数据库的任何更改都会改变执行计划，这会极大地影响时间。
了解更新数据库后时序差异的最好方法是对查询profile进行前后比较。在不知道您正在使用什么查询的情况下，尤其是在没有前后概要文件信息（均未提供）的情况下，很难不知道为什么更改了时间。
在几乎没有可用信息的情况下，唯一可以做出的猜测是时间已更改，因为数据库特征已以导致计划者更改执行计划的方式发生了改变。