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Bypass naive ordering when ordering by key (natural leveldb order) #22

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Bypass naive ordering when ordering by key (natural leveldb order) #22

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ec86d0d
bypass naive ordering when ordering by key (natural leveldb order).
raulk Jan 8, 2019
d844b5a
simplify with type switch.
raulk Jan 8, 2019
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7 changes: 7 additions & 0 deletions datastore.go
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Original file line number Diff line number Diff line change
Expand Up @@ -174,6 +174,13 @@ func (a *accessor) queryOrig(q dsq.Query) (dsq.Results, error) {
qr = dsq.NaiveFilter(qr, f)
}
for _, o := range q.Orders {
// leveldb iterators return entries sorted lexicographically by key, so we can bypass the naive ordering
// for OrderByKey. Since OrderByKey.Sort() has as struct receiver, the value stored in q.Orders can be a
// pointer or a struct, so we need to check for both for correctness.
switch o.(type) {
case dsq.OrderByKey, *dsq.OrderByKey:
continue
}
qr = dsq.NaiveOrder(qr, o)
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I believe we need OrderByKey to override other orders (this currently just skips these). Given that keys are unique and have a total order, I believe we should:

  1. Start at the end.
  2. Work backwards until we find the last OrderByKey.
  3. Apply any remaining orders.

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We could, in theory, optimize OrderByKeyDescending as well by taking advantage of the same total ordering. That is, stop at the last OrderByKeyDescending (if we reach one before we reach an OrderByKey). Unlike OrderByKey, we'll have to actually apply the OrderByKeyDescending order.

}
return qr, nil
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