default skiplist height same as original leveldb which had 4M write b…

…uffers. Raising to 17 to match Basho. Have seen 5% improvement in bsbm100m create. (#9)

Co-authored-by: MatthewVon <[email protected]>

memtable/inlineskiplist.h

@@ -72,7 +72,7 @@ class InlineSkipList {
   // in the allocator must remain allocated for the lifetime of the
   // skiplist object.
   explicit InlineSkipList(Comparator cmp, Allocator* allocator,
-                          int32_t max_height = 12,
+                          int32_t max_height = 17,
                           int32_t branching_factor = 4);
 
   // Allocates a key and a skip-list node, returning a pointer to the key

memtable/skiplist.h

@@ -50,7 +50,7 @@ class SkipList {
   // and will allocate memory using "*allocator".  Objects allocated in the
   // allocator must remain allocated for the lifetime of the skiplist object.
   explicit SkipList(Comparator cmp, Allocator* allocator,
-                    int32_t max_height = 12, int32_t branching_factor = 4);
+                    int32_t max_height = 17, int32_t branching_factor = 4);
 
   // Insert key into the list.
   // REQUIRES: nothing that compares equal to key is currently in the list.