Query Q23 (degree of parallelism: 2)

with frequent_ss_items as 
 (select substr(i_item_desc,1,30) itemdesc,i_item_sk item_sk,d_date solddate,count(*) cnt
  from store_sales
      ,date_dim 
      ,item
  where ss_sold_date_sk = d_date_sk
    and ss_item_sk = i_item_sk 
    and d_year in (2000,2000+1,2000+2,2000+3)
  group by substr(i_item_desc,1,30),i_item_sk,d_date
  having count(*) >4),
 max_store_sales as
 (select max(csales) tpcds_cmax 
  from (select c_customer_sk,sum(ss_quantity*ss_sales_price) csales
        from store_sales
            ,customer
            ,date_dim 
        where ss_customer_sk = c_customer_sk
         and ss_sold_date_sk = d_date_sk
         and d_year in (2000,2000+1,2000+2,2000+3) 
        group by c_customer_sk) t1),
 best_ss_customer as
 (select c_customer_sk,sum(ss_quantity*ss_sales_price) ssales
  from store_sales
      ,customer
  where ss_customer_sk = c_customer_sk
  group by c_customer_sk
  having sum(ss_quantity*ss_sales_price) > (50/100.0) * (select
  *
from
 max_store_sales))
  select  sum(sales)
 from (select cs_quantity*cs_list_price sales
       from catalog_sales
           ,date_dim 
       where d_year = 2000 
         and d_moy = 2 
         and cs_sold_date_sk = d_date_sk 
         and cs_item_sk in (select item_sk from frequent_ss_items)
         and cs_bill_customer_sk in (select c_customer_sk from best_ss_customer)
      union all
      select ws_quantity*ws_list_price sales
       from web_sales 
           ,date_dim 
       where d_year = 2000 
         and d_moy = 2 
         and ws_sold_date_sk = d_date_sk 
         and ws_item_sk in (select item_sk from frequent_ss_items)
         and ws_bill_customer_sk in (select c_customer_sk from best_ss_customer)) t2
 limit 100;
with frequent_ss_items as
 (select substr(i_item_desc,1,30) itemdesc,i_item_sk item_sk,d_date solddate,count(*) cnt
  from store_sales
      ,date_dim
      ,item
  where ss_sold_date_sk = d_date_sk
    and ss_item_sk = i_item_sk
    and d_year in (2000,2000 + 1,2000 + 2,2000 + 3)
  group by substr(i_item_desc,1,30),i_item_sk,d_date
  having count(*) >4),
 max_store_sales as
 (select max(csales) tpcds_cmax
  from (select c_customer_sk,sum(ss_quantity*ss_sales_price) csales
        from store_sales
            ,customer
            ,date_dim 
        where ss_customer_sk = c_customer_sk
         and ss_sold_date_sk = d_date_sk
         and d_year in (2000,2000+1,2000+2,2000+3)
        group by c_customer_sk) t1),
 best_ss_customer as
 (select c_customer_sk,sum(ss_quantity*ss_sales_price) ssales
  from store_sales
      ,customer
  where ss_customer_sk = c_customer_sk
  group by c_customer_sk
  having sum(ss_quantity*ss_sales_price) > (50/100.0) * (select
  *
 from max_store_sales))
  select  c_last_name,c_first_name,sales
 from (select c_last_name,c_first_name,sum(cs_quantity*cs_list_price) sales
        from catalog_sales
            ,customer
            ,date_dim 
        where d_year = 2000 
         and d_moy = 2 
         and cs_sold_date_sk = d_date_sk 
         and cs_item_sk in (select item_sk from frequent_ss_items)
         and cs_bill_customer_sk in (select c_customer_sk from best_ss_customer)
         and cs_bill_customer_sk = c_customer_sk 
       group by c_last_name,c_first_name
      union all
      select c_last_name,c_first_name,sum(ws_quantity*ws_list_price) sales
       from web_sales
           ,customer
           ,date_dim 
       where d_year = 2000 
         and d_moy = 2 
         and ws_sold_date_sk = d_date_sk 
         and ws_item_sk in (select item_sk from frequent_ss_items)
         and ws_bill_customer_sk in (select c_customer_sk from best_ss_customer)
         and ws_bill_customer_sk = c_customer_sk
       group by c_last_name,c_first_name) t2
     order by c_last_name,c_first_name,sales
  limit 100;

Measured execution times:
4000MB: -
4000MB-sp(lt0.2/ts5/min10/max100): -
8000MB: -
8000MB-sp(lt0.2/ts5/min10/max100): 144312