Batch updating a huge list causes OOM

 type Map = (String, Int)
 type Maps = Vector[Map]
 def insertMany(ms: Maps): ConnectionIO[Int] = {
   println(s"map size: ${ms.size}") //2312213
   val sql = "insert into collection (key, value) values (?, ?)"
   Update[Map](sql)
     .updateMany(ms)
 }

Above code causes OOM with memory settings: -Xms512m -Xmx1536m:

java.lang.OutOfMemoryError: Java heap space
    at scalaz.InvariantFunctor$class.$init$(InvariantFunctor.scala:46)
    at scalaz.FreeInstances$$anon$3.<init>(Free.scala:424)
    at scalaz.FreeInstances.freeMonad(Free.scala:424)
    at doobie.util.composite$LowerPriorityComposite$$anon$7$$anonfun$14.apply(composite.scala:119)
    at doobie.util.composite$LowerPriorityComposite$$anon$7$$anonfun$14.apply(composite.scala:119)
    at doobie.util.composite$LowerPriorityComposite$$anon$6$$anonfun$11.apply(composite.scala:109)
    at doobie.util.composite$LowerPriorityComposite$$anon$6$$anonfun$11.apply(composite.scala:109)
    at doobie.util.composite$LowerPriorityComposite$$anon$6$$anonfun$11.apply(composite.scala:109)
    at doobie.util.composite$LowerPriorityComposite$$anon$6$$anonfun$11.apply(composite.scala:109)
    at doobie.util.composite$LowerPriorityComposite$$anon$8$$anonfun$17.apply(composite.scala:129)
    at doobie.util.composite$LowerPriorityComposite$$anon$8$$anonfun$17.apply(composite.scala:129)
    at doobie.hi.preparedstatement$.set(preparedstatement.scala:222)
    at doobie.hi.preparedstatement$$anonfun$addBatchesAndExecute$1.apply(preparedstatement.scala:88)
    at doobie.hi.preparedstatement$$anonfun$addBatchesAndExecute$1.apply(preparedstatement.scala:88)
    at scala.collection.immutable.List$$anonfun$foldRight$1.apply(List.scala:397)
    at scala.collection.LinearSeqOptimized$class.foldLeft(LinearSeqOptimized.scala:124)
    at scala.collection.immutable.List.foldLeft(List.scala:84)
    at scala.collection.immutable.List.foldRight(List.scala:397)
    at doobie.hi.preparedstatement$.addBatchesAndExecute(preparedstatement.scala:88)
    at doobie.util.update$Update$class.updateMany(update.scala:113)
    at doobie.util.update$Update$$anon$5.updateMany(update.scala:198)
    at ...insertMany…

doobie-* versions:

[info] org.tpolecat:doobie-core_2.11:0.4.1
[info] org.tpolecat:doobie-hikari_2.11:0.4.1
[info] org.tpolecat:doobie-postgres_2.11:0.4.1

Start by reading doobie.hi.preparedstatement.addBatchesAndExecute and doobie.util.update.Update.updateMany, especially the stack-trace locations preparedstatement.scala:88 and update.scala:113. Reproduce the two-million-row update with doobie 0.4.1 and inspect memory use during batch construction. Done means large updateMany calls no longer exhaust the configured heap, with coverage for the reported case.