postgres=# explain analyze select random() from gp_dist_random('gp_id');  
                                                               QUERY PLAN                                                                  
-----------------------------------------------------------------------------------------------------------------------------------------  
 Gather Motion 240:1  (slice1; segments: 240)  (cost=0.00..4.00 rows=240 width=0)  
   Rows out:  240 rows at destination with 6.336 ms to first row, 59 ms to end, start offset by 4195 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 0.073 ms to first row, 0.075 ms to end, start offset by 4207 ms.  
 Slice statistics:  
   (slice0)    Executor memory: 471K bytes.  
   (slice1)    Executor memory: 163K bytes avg x 240 workers, 163K bytes max (seg0).  
 Statement statistics:  
   Memory used: 128000K bytes  
 Total runtime: 4279.445 ms  
(10 rows)