In FetchHeightRange, preallocate the hash array.

Change FetchBlockByHeight to do the database lookup itself instead of
calling getBlkByHeight.  This saves an allocation of the entire block,
which it wasn't using.

In OpenDB, use fetchBlockShaByHeight instead of getBlkByHeight since it
only needs the sha.  This saves memory on startup.

ok drahn@

ldb/block.go

@@ -247,13 +247,18 @@ func (db *LevelDb) FetchBlockShaByHeight(height int64) (sha *btcwire.ShaHash, er
 // fetchBlockShaByHeight returns a block hash based on its height in the
 // block chain.
 func (db *LevelDb) fetchBlockShaByHeight(height int64) (rsha *btcwire.ShaHash, err error) {
-	var sha *btcwire.ShaHash
+	key := int64ToKey(height)
-	sha, _, err = db.getBlkByHeight(height)
+
+	blkVal, err := db.lDb.Get(key, db.ro)
 	if err != nil {
-		return
+		log.Tracef("failed to find height %v", height)
+		return // exists ???
 	}
 
-	return sha, nil
+	var sha btcwire.ShaHash
+	sha.SetBytes(blkVal[0:32])
+
+	return &sha, nil
 }
 
 // FetchHeightRange looks up a range of blocks by the start and ending
@@ -271,7 +276,7 @@ func (db *LevelDb) FetchHeightRange(startHeight, endHeight int64) (rshalist []bt
 		endidx = endHeight
 	}
 
-	var shalist []btcwire.ShaHash
+	shalist := make([]btcwire.ShaHash, 0, endidx-startHeight)
 	for height := startHeight; height < endidx; height++ {
 		// TODO(drahn) fix blkFile from height
 

ldb/leveldb.go

@@ -101,7 +101,7 @@ func OpenDB(args ...interface{}) (btcdb.Db, error) {
 blockforward:
 	for {
 
-		sha, _, err := ldb.getBlkByHeight(testblock)
+		sha, err := ldb.fetchBlockShaByHeight(testblock)
 		if err == nil {
 			// block is found
 			lastSha = sha
@@ -125,7 +125,7 @@ blockforward:
 blocknarrow:
 	for lastknownblock != -1 {
 		testblock = (lastknownblock + nextunknownblock) / 2
-		sha, _, err := ldb.getBlkByHeight(testblock)
+		sha, err := ldb.fetchBlockShaByHeight(testblock)
 		if err == nil {
 			lastknownblock = testblock
 			lastSha = sha