Polars LazyFrames自动缓存机制为何未自动优化重复Join操作？

Polars为LazyFrames引入了自动缓存机制，按设计逻辑计划中存在重复LazyFrames时，无需手动执行缓存。但测试时发现该机制未达到预期最优效果：

无显式缓存示例 #

import polars as pl

df1 = pl.DataFrame({'id': [0,5,6]}).lazy()
df2 = pl.DataFrame({'id': [0,8,6]}).lazy()
df3 = pl.DataFrame({'id': [7,8,6]}).lazy()

df4 = df1.join(df2, on='id')
print(pl.concat([df4.join(df3, on='id'), df1,
                 df4]).explain())

对应的逻辑计划：

UNION
  PLAN 0:
    INNER JOIN:
    LEFT PLAN ON: [col("id")]
      INNER JOIN:
      LEFT PLAN ON: [col("id")]
        CACHE[id: a4bcf9591fefc837, count: 3]
          DF ["id"]; PROJECT 1/1 COLUMNS; SELECTION: "None"
      RIGHT PLAN ON: [col("id")]
        CACHE[id: 8cee8e3a6f454983, count: 1]
          DF ["id"]; PROJECT 1/1 COLUMNS; SELECTION: "None"
      END INNER JOIN
    RIGHT PLAN ON: [col("id")]
      DF ["id"]; PROJECT */1 COLUMNS; SELECTION: "None"
    END INNER JOIN
  PLAN 1:
    CACHE[id: a4bcf9591fefc837, count: 3]
      DF ["id"]; PROJECT 1/1 COLUMNS; SELECTION: "None"
  PLAN 2:
    INNER JOIN:
    LEFT PLAN ON: [col("id")]
      CACHE[id: a4bcf9591fefc837, count: 3]
        DF ["id"]; PROJECT 1/1 COLUMNS; SELECTION: "None"
    RIGHT PLAN ON: [col("id")]
      CACHE[id: 8cee8e3a6f454983, count: 1]
        DF ["id"]; PROJECT 1/1 COLUMNS; SELECTION: "None"
    END INNER JOIN
END UNION

有显式缓存示例 #

import polars as pl

df1 = pl.DataFrame({'id': [0,5,6]}).lazy()
df2 = pl.DataFrame({'id': [0,8,6]}).lazy()
df3 = pl.DataFrame({'id': [7,8,6]}).lazy()

df4 = df1.join(df2, on='id').cache()
print(pl.concat([df4.join(df3, on='id'), df1,
                 df4]).explain())

对应的逻辑计划：

UNION
  PLAN 0:
    INNER JOIN:
    LEFT PLAN ON: [col("id")]
      CACHE[id: 290661b0780, count: 18446744073709551615]
        FAST_PROJECT: [id]
          INNER JOIN:
          LEFT PLAN ON: [col("id")]
            DF ["id"]; PROJECT 1/1 COLUMNS; SELECTION: "None"
          RIGHT PLAN ON: [col("id")]
            DF ["id"]; PROJECT 1/1 COLUMNS; SELECTION: "None"
          END INNER JOIN
    RIGHT PLAN ON: [col("id")]
      DF ["id"]; PROJECT */1 COLUMNS; SELECTION: "None"
    END INNER JOIN
  PLAN 1:
    DF ["id"]; PROJECT */1 COLUMNS; SELECTION: "None"
  PLAN 2:
    CACHE[id: 290661b0780, count: 18446744073709551615]
      FAST_PROJECT: [id]
        INNER JOIN:
        LEFT PLAN ON: [col("id")]
          DF ["id"]; PROJECT 1/1 COLUMNS; SELECTION: "None"
        RIGHT PLAN ON: [col("id")]
          DF ["id"]; PROJECT 1/1 COLUMNS; SELECTION: "None"
        END INNER JOIN
END UNION

从结果可见，显式缓存时df1与df2的Join仅执行一次，逻辑计划更高效。为什么Polars的自动缓存机制无法检测到Join操作的重复使用并自动缓存？是我遗漏了什么细节吗？

内容的提问来源于stack exchange，提问作者barak1412