From c9686a7f24600c71528252444bdd8136676917ac Mon Sep 17 00:00:00 2001
From: "Sascha L. Teichmann" <sascha.teichmann@intevation.de>
Date: Fri, 24 Jul 2015 13:15:05 +0200
Subject: [PATCH] Fixed non-interleaved LevelDB backend.

---
 cmd/mtredisalize/leveldb.go | 40 +++++++++++++++----------------------
 1 file changed, 16 insertions(+), 24 deletions(-)

diff --git a/cmd/mtredisalize/leveldb.go b/cmd/mtredisalize/leveldb.go
index caf0977..a03c6a9 100644
--- a/cmd/mtredisalize/leveldb.go
+++ b/cmd/mtredisalize/leveldb.go
@@ -314,42 +314,34 @@ func (ldbs *LevelDBSession) plainSpatialQuery(
 
 		ro := leveldb.NewReadOptions()
 		defer ro.Close()
-		ro.SetFillCache(false)
-
-		it := ldbs.backend.db.NewIterator(ro)
-		defer it.Close()
 
 		var a, b common.Coord
-		var err error
 
 		for _, r := range ldbs.backend.coverage.Query(c1, c2) {
 			a.Z, b.Z = int16(r.Z), int16(r.Z)
 			a.X, b.X = int16(r.X1), int16(r.X2)
-			// log.Printf("y1 y2 x1 x2 z: %d %d, %d %d, %d\n", r.Y1, r.Y2, r.X1, r.X2, r.Z)
 			for a.Y = r.Y2; a.Y >= r.Y1; a.Y-- {
 				b.Y = a.Y
-				from, to := common.CoordToPlain(a), common.CoordToPlain(b)
-				it.Seek(common.StringToBytes(from))
-				for ; it.Valid(); it.Next() {
-					key := it.Key()
-					var pos int64
-					if pos, err = common.DecodeStringFromBytes(key); err != nil {
-						log.Printf("decoding key failed: %s\n", err)
+				// The keys in the database are stored and ordered as strings
+				// "1", "10", ..., "19", "2", "20", "21" so you cannot use
+				// an iterator and assume it is numerical ordered.
+				// Each block is fetched with a Get instead.
+				for f, t := common.CoordToPlain(a), common.CoordToPlain(b); f <= t; f++ {
+					key := common.StringToBytes(f)
+					value, err := ldbs.backend.db.Get(ro, key)
+					if err != nil {
+						log.Printf("get failed: %s\n", err)
 						return
 					}
-					if pos > to {
-						break
-					}
-					select {
-					case blocks <- Block{Key: key, Data: it.Value()}:
-					case <-done:
-						return
+					if value != nil {
+						select {
+						case blocks <- Block{Key: key, Data: value}:
+						case <-done:
+							return
+						}
 					}
 				}
-				if err = it.GetError(); err != nil {
-					log.Printf("iterating failed: %s\n", err)
-					return
-				}
+
 			}
 		}
 	}()