Addresses #106 by adding experimental locking in this case

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 Only accretive/fixative changes will be made from now on.
 
+The following changes have been made on **master** since the 1.0.424 release:
+
+* Add MySQL-specific result set streaming tip.
+* Investigate possible solutions for #106 (mutable transaction thread safety) -- experimental `locking` on `Connection` object.
+
 ## Stable Builds
 
 * 2020-04-10 -- 1.0.424

src/next/jdbc/transaction.clj

@@ -82,7 +82,8 @@
 (extend-protocol p/Transactable
   java.sql.Connection
   (-transact [this body-fn opts]
-             (transact* this body-fn opts))
+             (locking this
+                      (transact* this body-fn opts)))
   javax.sql.DataSource
   (-transact [this body-fn opts]
              (with-open [con (p/get-connection this opts)]