title: apoc.periodic.iterate fails when parallel = true
body: <pre><code>CALL apoc.periodic.iterate(&quot;
  CALL apoc.load.csv('/data/keywordOf.csv', {nullValues:['','na',false], sep:'    '}) 
  yield map as row &quot;, 
  &quot;MATCH (h:keyword{nid: row._start})
  MATCH (t:text{nid: row._end})
  CALL apoc.merge.relationship(h, row._type, {}, {}, t, {}) yield rel
  RETURN rel&quot;, {batchSize:1000, iterateList:true, parallel:true})
  </code></pre>
  <p>If I execute this query in Neo4j Browser, it gives the error message:</p>
  <pre><code>&quot;LockClient[64403] can't wait on resource RWLock[NODE(16710), hash=1723282586] since =&gt; LockClient[64403] &lt;-[:held_by]- rwlock[node(16775), hash=&quot;2010716140]&quot; lockclient[64402] rwlock[node(16710), 1, &quot;lockclient[64405] can't wait on resource rwlock[node(16714), since&gt; LockClient[64405] &lt;-[:held_by]- rwlock[node(16710), hash=&quot;654905318]&quot; lockclient[64406] rwlock[node(16714), 1, &quot;lockclient[64409] can't wait on resource since&gt; LockClient[64409] &lt;-[:held_by]- rwlock[node(16715), hash=&quot;1512035086]&quot; lockclient[64406] rwlock[node(16714), 1, &quot;lockclient[64404] can't wait on resource rwlock[node(16868), since&gt; LockClient[64404] &lt;-[:held_by]- rwlock[node(16715), hash=&quot;1512035086]&quot; lockclient[64409] rwlock[node(16868), 1, &quot;lockclient[64408] can't wait on resource rwlock[node(17045), since&gt; LockClient[64408] &lt;-[:held_by]- rwlock[node(16710), hash=&quot;1723282586]&quot; lockclient[64407] rwlock[node(16760), lockclient[64409] rwlock[node(16759), lockclient[64405] rwlock[node(17045), 1, &quot;lockclient[64402] can't wait on resource since&gt; LockClient[64402] &lt;-[:held_by]- rwlock[node(16710), hash=&quot;1723282586]&quot; lockclient[64407] rwlock[node(16760), 1, &quot;lockclient[64407] can't wait on resource rwlock[node(17151), since&gt; LockClient[64407] &lt;-[:held_by]- rwlock[node(17096), hash=&quot;1651176694]&quot; lockclient[64404] rwlock[node(17151), 1, &quot;lockclient[64410] can't wait on resource rwlock[node(16757), since&gt; LockClient[64410] &lt;-[:held_by]- rwlock[node(16712), hash=&quot;727900967]&quot; lockclient[64408] rwlock[node(16710), lockclient[64407] rwlock[node(16757), 1, &quot;lockclient[64411] can't wait on resource rwlock[node(17040), since&gt; LockClient[64411] &lt;/-[:held_by]-&gt;&lt;/-[:held_by]-&gt;&lt;/-[:held_by]-&gt;&lt;/-[:held_by]-&gt;&lt;/-[:held_by]-&gt;&lt;/-[:held_by]-&gt;&lt;/-[:held_by]-&gt;&lt;/-[:held_by]-&gt;
  </code></pre>
  <p>In the batch column, it shows:</p>
  <pre><code> &quot;total&quot;: 12,
    &quot;committed&quot;: 3,
    &quot;failed&quot;: 9,
  </code></pre>
  <p>Why can't I use parallel:true to merge relationships.</p>