nickva opened a new pull request, #6032:
URL: https://github.com/apache/couchdb/pull/6032
The idea of doc/shard grouping and rotation was that different databases
would start their workers on different copies, spread those uniformly and
consistently by `{Range, DbName}`.
However, the order of entries were actually dependent on `dict:to_list/1`
internals. So, if `dict` was changed to return sorted items, like for instance
maps do, we'd end up suddently breaking the supposedly randomized spread (I
found this out by actually trying to use a map there instead of a dict).
To fix this, make the rotation explicit. Group the entries first, then sort
each group, and then rotate by `{Range, DbName}`.
While at it make it so we don't have to duplicate the main rotate function
in tests and use the actual function we intend to test.
Add some explicit tests for this behavior. One downside is those tests rely
on the exact rotate_list/2 implementation (`crc32(?term_to_binary/1`) so if
that changes we'll know and have to update the test.
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