换句话说，激活深度表示从根对象中标识的引用总数，db4o将在查询中遍历根对象并返回结果。

In other words, activation depth is a count of the number of references identified from the root object that db4o will traverse and return as part of a query.

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histo产生一个对象文本柱状图，现在在堆中大量引用，由特定类型消耗的字节总数分类。

Histo produces a text histogram of the objects currently strongly referenced in the heap, sorted by the total number of bytes consumed by that particular type.

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