Github user joshelser commented on a diff in the pull request:
https://github.com/apache/accumulo/pull/33#discussion_r29161718
--- Diff: docs/src/main/asciidoc/chapters/iterator_design.txt ---
@@ -145,8 +146,16 @@ alter the internal state of the Iterator.
These methods simply return the current Key-Value pair for this iterator.
If `hasTop` returns true,
both of these methods should return non-null objects. If `hasTop` returns
false, it is undefined
-what these methods should return. Multiple calls to these methods should
not alter the state
-of the Iterator like `hasTop`.
+what these methods should return. Like `hasTop`, multiple calls to these
methods should not alter
+the state of the Iterator.
+
+When saving a Key or Value from a source iterator's `getTopKey` or
`getTopValue` methods
+for use after calling `next` on the source iterator (e.g., when cacheing
keys or values
+from the source iterator), it is important to copy the Key or Value into a
new object
+because the source iterator may reuse the Key or Value objects for
performance reasons.
--- End diff --
Great, thanks Dylan. My memory isn't what it should be :).
> I think some iterators do this frequently
I took a gander at the "user" iterators, and I was a little surprised to
see as many iterators doing a copy in some form or another. Perhaps I'm being
overly sensitive on the performance concerns. Maybe my concern could be
reworded: are there cases in which a user doesn't need to copy the Key we could
outline?
"An iterator which doesn't modify the Key from its source doesn't need to
copy it" ? This would catch cases like value transformations. What do you
think? Is that a safe clarification to make?
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