我最近将neo4j从2.1.7更新到2.2.5。我发现了那个查询
Match (c:C) where id(c) = 111 with c Match (p:I{id: c.id}) return count(p)
在2.1.7中运行良好，但在2.2.5（100倍长）中表现很差。我有所需的所有索引。 我将此查询修改为
Match (c:C) where id(c) = 111 with c.id as c_id Match (p:I{id: c_id}) return count(p)
在此之后它在2.2.5中正常工作 这两个查询有不同的配置文件。但我对分析并不十分满意。
已更新 更奇怪的是，如果我使用explain而不是profile - 它可以快速运行。
neo4j-sh (?)$ PROFILE Match (c:C) where id(c) = 10563822 with c Match (i:I{id: c.id}) return count(i);
==> +----------+
==> | count(i) |
==> +----------+
==> | 4551 |
==> +----------+
==> 1 row
==> 18257 ms
==>
==> Compiler CYPHER 2.2
==>
==> Planner COST
==>
==> EagerAggregation
==> |
==> +Filter(0)
==> |
==> +CartesianProduct
==> |
==> +Filter(1)
==> | |
==> | +NodeByIdSeek
==> |
==> +NodeByLabelScan
==>
==> +------------------+---------------+---------+---------+-------------+-------------------------+
==> | Operator | EstimatedRows | Rows | DbHits | Identifiers | Other |
==> +------------------+---------------+---------+---------+-------------+-------------------------+
==> | EagerAggregation | 26 | 1 | 0 | count(i) | |
==> | Filter(0) | 652 | 4551 | 2522988 | c, i | i.id == c.id |
==> | CartesianProduct | 6521 | 1261494 | 0 | c, i | |
==> | Filter(1) | 0 | 1 | 1 | c | c:C |
==> | NodeByIdSeek | 1 | 1 | 1 | c | |
==> | NodeByLabelScan | 1261494 | 1261494 | 1261495 | i | :I |
==> +------------------+---------------+---------+---------+-------------+-------------------------+
==>
==> Total database accesses: 3784485
sh (?)$ PROFILE Match (c:C) where id(c) = 10563822 with c.id as c_id Match (i:I{id: c_id}) return count(i);
==> +----------+
==> | count(i) |
==> +----------+
==> | 4551 |
==> +----------+
==> 1 row
==> 64 ms
==>
==> Compiler CYPHER 2.2
==>
==> Planner COST
==>
==> EagerAggregation
==> |
==> +Apply
==> |
==> +Projection
==> | |
==> | +Filter
==> | |
==> | +NodeByIdSeek
==> |
==> +NodeIndexSeek
==>
==> +------------------+---------------+------+--------+-------------+---------------------+
==> | Operator | EstimatedRows | Rows | DbHits | Identifiers | Other |
==> +------------------+---------------+------+--------+-------------+---------------------+
==> | EagerAggregation | 1 | 1 | 0 | count(i) | |
==> | Apply | 1 | 4551 | 0 | c, c_id, i | |
==> | Projection | 0 | 1 | 1 | c, c_id | c.id |
==> | Filter | 0 | 1 | 1 | c | c:C |
==> | NodeByIdSeek | 1 | 1 | 1 | c | |
==> | NodeIndexSeek | 1 | 4551 | 4552 | i | :I(id) |
==> +------------------+---------------+------+--------+-------------+---------------------+
==>
==> Total database accesses: 4555
答案 0 :(得分：0)
我没有足够的neo4j内部知识知道为什么你的查询在较新的版本中较慢（CartesianProduct步骤似乎是一个红色标志），但这里是一个逻辑上等效的查询，似乎它应该要快得多：
START c = node(111)
MATCH (p:I { id: c.id })
RETURN count(p)
以下是个人资料：
+------------------+------+--------+----------------------------------------------------------+-----------------------+
| Operator | Rows | DbHits | Identifiers | Other |
+------------------+------+--------+----------------------------------------------------------+-----------------------+
| ColumnFilter | 1 | 0 | count(p) | keep columns count(p) |
| EagerAggregation | 1 | 0 | INTERNAL_AGGREGATE51b25e53-027d-439b-9046-c1a2a6b0fe70 | |
| Filter | 0 | 0 | c, p | p.id == c.id |
| NodeById | 0 | 0 | c, p | Literal(List(111)) |
| NodeByLabel | 0 | 1 | p | :I |
+------------------+------+--------+----------------------------------------------------------+-----------------------+
注意：这应该被视为一种临时解决方法，因为START已被弃用，我不知道这种用法将继续得到多长时间的支持。