Use config:get_integer/3 in couch_btree

Previously we used config:get/3 as that was probably before we had
config:get_integer/3 implemented.

The compile "inline" is also not adding much but left it in there for now.
Benchmarking it, it save at most 10 nanoseconds at most per call when
making 100M calls in a row (0.144744 usec vs 0.15082468 usec per call).

Author: nickva

src/couch/src/couch_btree.erl

@@ -20,6 +20,8 @@
 
 -include_lib("couch/include/couch_db.hrl").
 
+-define(DEFAULT_CHUNK_SIZE, 1279).
+
 % For the btree cache, the priority of the root node will be
 % this value. The priority is roughly how many cleanup interval
 % (second) they'll survive without any updates in the cache
@@ -463,12 +465,7 @@ chunkify([InElement | RestInList], ChunkThreshold, OutList, OutListSize, OutputC
 
 -compile({inline, [get_chunk_size/0]}).
 get_chunk_size() ->
-    try
-        list_to_integer(config:get("couchdb", "btree_chunk_size", "1279"))
-    catch
-        error:badarg ->
-            1279
-    end.
+    config:get_integer("couchdb", "btree_chunk_size", ?DEFAULT_CHUNK_SIZE).
 
 modify_node(Bt, RootPointerInfo, Actions, QueryOutput, Depth0) ->
     Depth = Depth0 + 1,