Add transaction buffer filter.

impl/memory/gkvlite_iter.go

Index: impl/memory/gkvlite_iter.go
diff --git a/impl/memory/gkvlite_iter.go b/impl/memory/gkvlite_iter.go
index f75ca02d248d2d965e31e37192912ee18b1ceda9..2d2419c26db0659a10a83a66865cad65231ba321 100644
--- a/impl/memory/gkvlite_iter.go
+++ b/impl/memory/gkvlite_iter.go
@@ -65,7 +65,8 @@ func multiIterate(defs []*iterDefinition, cb func(suffix []byte) bool) {
 			}
 			def := defs[idx]
 
-			it.next(serialize.Join(def.prefix, suffix), func(itm *gkvlite.Item) {
+			pfxLen := prefixLens[idx]
+			it.next(serialize.Join(def.prefix[:pfxLen], suffix), func(itm *gkvlite.Item) {

[iannucci, 2015/09/29 04:43:27]

This bug happens when using builtin indexes for queries with inequalities on
__key__ and also ancestor filters AND where the multiIterator query needs to
skip some rows. It happens because the bytes for the ancestor key don't reflect
in pfxLen (on purpose, see datastore_index_selection). I was correctly creating
sfxRO below, but failed to do the same here.

 				if itm == nil {
 					// we hit the end of an iterator, we're now done with the whole
 					// query.
@@ -73,7 +74,7 @@ func multiIterate(defs []*iterDefinition, cb func(suffix []byte) bool) {
 					return
 				}
 
-				sfxRO := itm.Key[prefixLens[idx]:]
+				sfxRO := itm.Key[pfxLen:]
 
 				if bytes.Compare(sfxRO, suffix) > 0 {
 					// this row has a higher suffix than anything we've seen before. Set