improve

Author: digoal

201801/20180127_01.md

@@ -408,40 +408,34 @@ postgres=# explain select rb_and_agg(bitmap) from tbl where tagid in (1,2,3,4,5,
 
 ## roaring bitmap空间评估
 ```
-postgres=# select pg_column_size(rb_build(array(select (random()*2000000000)::int from generate_series(1,100)))) ;
+postgres=# select pg_column_size(rb_build(array(select ((random()*4000000000)::int8-2000000000)::int from generate_series(1,1000)))) ;
  pg_column_size 
 ----------------
-           1012
+           9972
 (1 row)
 
-postgres=# select pg_column_size(rb_build(array(select (random()*2000000000)::int from generate_series(1,1000)))) ;
+postgres=# select pg_column_size(rb_build(array(select ((random()*4000000000)::int8-2000000000)::int from generate_series(1,10000)))) ;
  pg_column_size 
 ----------------
-           9916
+          93588
 (1 row)
 
-postgres=# select pg_column_size(rb_build(array(select (random()*2000000000)::int from generate_series(1,10000)))) ;
+postgres=# select pg_column_size(rb_build(array(select ((random()*4000000000)::int8-2000000000)::int from generate_series(1,100000)))) ;
  pg_column_size 
 ----------------
-          87828
+         593094
 (1 row)
 
-postgres=# select pg_column_size(rb_build(array(select (random()*2000000000)::int from generate_series(1,100000)))) ;
+postgres=# select pg_column_size(rb_build(array(select ((random()*4000000000)::int8-2000000000)::int from generate_series(1,1000000)))) ;
  pg_column_size 
 ----------------
-         435110
+        2487818
 (1 row)
 
-postgres=# select pg_column_size(rb_build(array(select (random()*2000000000)::int from generate_series(1,1000000)))) ;
+postgres=# select pg_column_size(rb_build(array(select ((random()*4000000000)::int8-2000000000)::int from generate_series(1,10000000)))) ;
  pg_column_size 
 ----------------
-        2243610
-(1 row)
-
-postgres=# select pg_column_size(rb_build(array(select (random()*2000000000)::int from generate_series(1,10000000)))) ;
- pg_column_size 
-----------------
-       20191636
+       20441260
 (1 row)
 ```