Scala：什么是CompactBuffer？

Question

我试图找出CompactBuffer的含义。它和迭代器一样吗？

请解释不同之处。

Answer 1

根据Spark的文档，它是ArrayBuffer的替代品，可以提供更好的性能，因为它可以分配更少的内存。

以下是CompactBuffer类文档的摘录：

/**
* An append-only buffer similar to ArrayBuffer, but more memory-efficient for small buffers.
* ArrayBuffer always allocates an Object array to store the data, with 16 entries by default,
* so it has about 80-100 bytes of overhead. In contrast, CompactBuffer can keep up to two
* elements in fields of the main object, and only allocates an Array[AnyRef] if there are more
* entries than that. This makes it more efficient for operations like groupBy where we expect
* some keys to have very few elements.
*/