Dear Basex team,
We are facing an xquery performance issue. Please find the query in below and please suggest any clue to optimize query

     let $subbrk := (collection("867509_Voice_DECEMBER-19_Billed_1")/SUBCUSTBRK)
     let $detailUsageTxn := $subbrk/DETAIL/TRANSACTION[@Usage = 'usage']

      let $DistCallTypesAll := ($detailUsageTxn/SUB_SECTION/@Type)
      let $DistCallTypes :=  ( for $r in $DistCallTypesAll   group by $ct :=  $r return $ct)

//Here taking nearly 3 minutes

        let $allmonths := distinct-values($subbrk/Month)
       let $rowcnt := count($detailUsageTxn/SUB_SECTION)
       let $months := $allmonths[position() le 10000]
       let $opttype := 'NumVal'
        let $durop := 'hh:mm:ss' return  
         (  
            if($DistCallTypes!=''
          )
          then(
                for $month in $months
                    return    
                    <R>       
                           <GRPBY>{ $month }</GRPBY>{                
                            if($opttype = 'NumVal') then                    
                                for $ct in $DistCallTypes                    
                                let $ctCnt := sum($detailUsageTxn/SUB_SECTION[data(@Type) = data($ct) and data(../../../Month) = $month]/@Calls)        
//Here taking 4 to 5 minutes         
                                 return element
                                     { replace(concat('_',data($ct)),'(\.|\[|\]|\\|\||\-|\^|\$|\?|\*|\+|\{|\}|\(|\)| |&apos;)', '_') }
                                      {xs:decimal($ctCnt)}    
                                     else ()                
                                }  
 
                     </R>)
            else()      
      ) 



Regards,
Chandrasekhar