FT-93 Fix a bug with aligned pivotkeys where we may overestimate how

much space is needed on disk

ft/ft-ops.cc

@@ -540,7 +540,7 @@ ftnode_memory_size (FTNODE node)
     int n_children = node->n_children;
     retval += sizeof(*node);
     retval += (n_children)*(sizeof(node->bp[0]));
-    retval += node->pivotkeys.total_size();
+    retval += node->pivotkeys.serialized_size();
 
     // now calculate the sizes of the partitions
     for (int i = 0; i < n_children; i++) {

ft/pivotkeys.cc

@@ -436,7 +436,7 @@ void ftnode_pivot_keys::serialize_to_wbuf(struct wbuf *wb) const {
         wbuf_nocrc_bytes(wb, fixed ? _fixed_key(i) : _dbt_keys[i].data, size);
         written += size;
     }
-    invariant(written == _total_size);
+    invariant(written == serialized_size());
 }
 
 int ftnode_pivot_keys::num_pivots() const {
@@ -450,3 +450,9 @@ size_t ftnode_pivot_keys::total_size() const {
     paranoid_invariant(_fixed_keys == nullptr || (_total_size == _fixed_keylen_aligned * _num_pivots));
     return _total_size;
 }
+
+size_t ftnode_pivot_keys::serialized_size() const {
+    // we only return the size that will be used when serialized, so we calculate based
+    // on the fixed keylen and not the aligned keylen.
+    return _fixed_format() ? _num_pivots * _fixed_keylen : _total_size;
+}