postgres=# explain analyze select random() from gp_dist_random('gp_id') limit 1;  
                                                                  QUERY PLAN                                                                     
-----------------------------------------------------------------------------------------------------------------------------------------------  
 Limit  (cost=0.00..0.04 rows=1 width=0)  
   Rows out:  1 rows with 5.865 ms to first row, 5.884 ms to end, start offset by 4212 ms.  
   ->  Gather Motion 240:1  (slice1; segments: 240)  (cost=0.00..0.04 rows=1 width=0)  
         Rows out:  1 rows at destination with 5.857 ms to end, start offset by 4212 ms.  
         ->  Limit  (cost=0.00..0.02 rows=1 width=0)  
               Rows out:  Avg 1.0 rows x 240 workers.  Max 1 rows (seg0) with 0.062 ms to first row, 0.063 ms to end, start offset by 4228 ms.  
               ->  Seq Scan on gp_id  (cost=0.00..4.00 rows=1 width=0)  
                     Rows out:  Avg 1.0 rows x 240 workers.  Max 1 rows (seg0) with 0.060 ms to end, start offset by 4228 ms.  
 Slice statistics:  
   (slice0)    Executor memory: 463K bytes.  
   (slice1)    Executor memory: 163K bytes avg x 240 workers, 163K bytes max (seg0).  
 Statement statistics:  
   Memory used: 128000K bytes  
 Total runtime: 4288.007 ms  
(14 rows)