Github user afs commented on the issue:
https://github.com/apache/jena/pull/306
Revised version.
The co-iteration algorithm (choice 3) is complicated. Determining the right
thing to do each time is expensive and still a pragmatic choice with graph
probing. The app may well know what to do so call the appropriate method as
already documented.
My suggestion is algorithm 2 (a slightly improved version of the patch on
JENA-1414), document what to do if src is a large persistent database and
remove the complicate algorithm 3.
If that is our decision, I will produce a much simpler commit for algorithm
2.
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