approach to persistent queue on MarkLogic (untested!)

gistfile1.xq

xquery version "1.0-ml";

declare variable $flush := 1;

declare function local:queue($map){
if ($flush eq 1 or fn:empty(xdmp:get-server-field('queue'))) then
  let $queue as map:map  := map:map( if ($map) then $map else <map:map/>)
  let $serverfield := xdmp:set-server-field('queue',$queue)
  return
    $queue
else
  map:map(xdmp:get-server-field('queue'))
  };

declare function local:queue-put($key,$val){
let $q as map:map := xdmp:get-server-field('queue')
let $p := map:put($q,$key,$val)
return
  xdmp:set-server-field('queue',$q)
};

declare function local:queue-get($key){
let $q := map:map(xdmp:get-server-field('queue'))
return
  map:get($q,$key)
};

 local:queue(<map:map/>
(: run above first to init persistent queue, then the following
local:queue-put('1','test'),
local:queue-get('1')
:)