路径 ID

PATH ID 是 Vertica 为查询计划内的每个操作（路径）所分配的唯一标识符。以下项共享同一标识符：

• 查询计划

• 联接错误消息

• 系统表 执行_引擎_配置文件 和 QUERY_PLAN_PROFILES

路径 ID 可帮助您追踪问题的根本原因。例如，如果查询返回联接错误，请在查询前加上 EXPLAIN 并在查询计划中查找 PATH ID n，以查看查询中的哪个联接有问题。

例如，下面的 EXPLAIN 输出显示优化器查询计划中每个路径的路径 ID：

=> EXPLAIN SELECT * FROM fact JOIN dim ON x=y JOIN ext on y=z;
 Access Path:
 +-JOIN MERGEJOIN(inputs presorted) [Cost: 815, Rows: 10K (NO STATISTICS)] (PATH ID: 1)
 | Join Cond: (dim.y = ext.z)
 | Materialize at Output: fact.x
 | Execute on: All Nodes
 | +-- Outer -> JOIN MERGEJOIN(inputs presorted) [Cost: 408, Rows: 10K (NO STATISTICS)] (PATH ID: 2)
 | | Join Cond: (fact.x = dim.y)
 | | Execute on: All Nodes
 | | +-- Outer -> STORAGE ACCESS for fact [Cost: 202, Rows: 10K (NO STATISTICS)] (PATH ID: 3)
 | | | Projection: public.fact_super
 | | | Materialize: fact.x
 | | | Execute on: All Nodes
 | | +-- Inner -> STORAGE ACCESS for dim [Cost: 202, Rows: 10K (NO STATISTICS)] (PATH ID: 4)
 | | | Projection: public.dim_super
 | | | Materialize: dim.y
 | | | Execute on: All Nodes
 | +-- Inner -> STORAGE ACCESS for ext [Cost: 202, Rows: 10K (NO STATISTICS)] (PATH ID: 5)
 | | Projection: public.ext_super
 | | Materialize: ext.z
 | | Execute on: All Nodes