Update testingandtuning.mdx

product_docs/docs/pgd/5/testingandtuning.mdx

@@ -108,7 +108,7 @@ responsibility to suppress them by setting appropriate variables, such as `clien
 PGD allows you to issue write transactions onto multiple nodes. Bringing
 those writes back together onto each node has a performance cost.
 
-First, replaying changes from another node has a CPU cost, an I/O cost,
+First, replaying changes from another node has a CPU cost and an I/O cost,
 and it generates WAL records. The resource use is usually less
 than in the original transaction since CPU overhead is lower as a result
 of not needing to reexecute SQL. In the case of UPDATE and DELETE