Doc: fix incorrect EXPLAIN ANALYZE output for bloom indexes

It looks like the example case was once modified to increase the number
of rows but the EXPLAIN ANALYZE output wasn't updated to reflect that.

Also adjust the text which discusses the index sizes.  With the example
table size, the bloom index isn't quite 8 times more space efficient
than the btree indexes.

Discussion: https://postgr.es/m/CAApHDvovx8kQ0=HTt85gFDAwmTJHpCgiSvRmQZ_6u_g-vQYM_w@mail.gmail.com
Back-through: 13, all supported versions

diff --git a/doc/src/sgml/bloom.sgml b/doc/src/sgml/bloom.sgml
index 19f2b172cc4fbc1f3703262a5c881f06b4ac6425..0e734f3d6e685fda3d579994be97f42eda41729e 100644 (file)
--- a/doc/src/sgml/bloom.sgml
+++ b/doc/src/sgml/bloom.sgml
@@ -118,11 +118,11 @@ SELECT 10000000
 =# EXPLAIN ANALYZE SELECT * FROM tbloom WHERE i2 = 898732 AND i5 = 123451;
                                               QUERY PLAN
 -------------------------------------------------------------------&zwsp;-----------------------------------
- Seq Scan on tbloom  (cost=0.00..2137.14 rows=3 width=24) (actual time=16.971..16.971 rows=0 loops=1)
+ Seq Scan on tbloom  (cost=0.00..213744.00 rows=250 width=24) (actual time=357.059..357.059 rows=0 loops=1)
    Filter: ((i2 = 898732) AND (i5 = 123451))
-   Rows Removed by Filter: 100000
+   Rows Removed by Filter: 10000000
  Planning Time: 0.346 ms
- Execution Time: 16.988 ms
+ Execution Time: 357.076 ms
 (5 rows)
 </programlisting>
   </para>
@@ -136,16 +136,16 @@ CREATE INDEX
 =# SELECT pg_size_pretty(pg_relation_size('btreeidx'));
  pg_size_pretty
 ----------------
- 3976 kB
+ 386 MB
 (1 row)
 =# EXPLAIN ANALYZE SELECT * FROM tbloom WHERE i2 = 898732 AND i5 = 123451;
                                               QUERY PLAN
 -------------------------------------------------------------------&zwsp;-----------------------------------
- Seq Scan on tbloom  (cost=0.00..2137.00 rows=2 width=24) (actual time=12.805..12.805 rows=0 loops=1)
+ Seq Scan on tbloom  (cost=0.00..213744.00 rows=2 width=24) (actual time=351.016..351.017 rows=0 loops=1)
    Filter: ((i2 = 898732) AND (i5 = 123451))
-   Rows Removed by Filter: 100000
+   Rows Removed by Filter: 10000000
  Planning Time: 0.138 ms
- Execution Time: 12.817 ms
+ Execution Time: 351.035 ms
 (5 rows)
 </programlisting>
   </para>
@@ -159,19 +159,19 @@ CREATE INDEX
 =# SELECT pg_size_pretty(pg_relation_size('bloomidx'));
  pg_size_pretty
 ----------------
- 1584 kB
+ 153 MB
 (1 row)
 =# EXPLAIN ANALYZE SELECT * FROM tbloom WHERE i2 = 898732 AND i5 = 123451;
                                                      QUERY PLAN
 -------------------------------------------------------------------&zwsp;--------------------------------------------------
- Bitmap Heap Scan on tbloom  (cost=1792.00..1799.69 rows=2 width=24) (actual time=0.388..0.388 rows=0 loops=1)
+ Bitmap Heap Scan on tbloom  (cost=1792.00..1799.69 rows=2 width=24) (actual time=22.605..22.606 rows=0 loops=1)
    Recheck Cond: ((i2 = 898732) AND (i5 = 123451))
-   Rows Removed by Index Recheck: 29
-   Heap Blocks: exact=28
-   -&gt;  Bitmap Index Scan on bloomidx  (cost=0.00..1792.00 rows=2 width=0) (actual time=0.356..0.356 rows=29 loops=1)
+   Rows Removed by Index Recheck: 2300
+   Heap Blocks: exact=2256
+   -&gt;  Bitmap Index Scan on bloomidx  (cost=0.00..178436.00 rows=1 width=0) (actual time=20.005..20.005 rows=2300 loops=1)
          Index Cond: ((i2 = 898732) AND (i5 = 123451))
  Planning Time: 0.099 ms
- Execution Time: 0.408 ms
+ Execution Time: 22.632 ms
 (8 rows)
 </programlisting>
   </para>
@@ -197,21 +197,21 @@ CREATE INDEX
 =# EXPLAIN ANALYZE SELECT * FROM tbloom WHERE i2 = 898732 AND i5 = 123451;
                                                         QUERY PLAN
 -------------------------------------------------------------------&zwsp;--------------------------------------------------------
- Bitmap Heap Scan on tbloom  (cost=24.34..32.03 rows=2 width=24) (actual time=0.028..0.029 rows=0 loops=1)
+ Bitmap Heap Scan on tbloom  (cost=9.29..13.30 rows=1 width=24) (actual time=0.032..0.033 rows=0 loops=1)
    Recheck Cond: ((i5 = 123451) AND (i2 = 898732))
-   -&gt;  BitmapAnd  (cost=24.34..24.34 rows=2 width=0) (actual time=0.027..0.027 rows=0 loops=1)
-         -&gt;  Bitmap Index Scan on btreeidx5  (cost=0.00..12.04 rows=500 width=0) (actual time=0.026..0.026 rows=0 loops=1)
+   -&gt;  BitmapAnd  (cost=9.29..9.29 rows=1 width=0) (actual time=0.047..0.047 rows=0 loops=1)
+         -&gt;  Bitmap Index Scan on btreeidx5  (cost=0.00..4.52 rows=11 width=0) (actual time=0.026..0.026 rows=7 loops=1)
                Index Cond: (i5 = 123451)
-         -&gt;  Bitmap Index Scan on btreeidx2  (cost=0.00..12.04 rows=500 width=0) (never executed)
+         -&gt;  Bitmap Index Scan on btreeidx2  (cost=0.00..4.52 rows=11 width=0) (actual time=0.007..0.007 rows=8 loops=1)
                Index Cond: (i2 = 898732)
- Planning Time: 0.491 ms
- Execution Time: 0.055 ms
+ Planning Time: 0.264 ms
+ Execution Time: 0.047 ms
 (9 rows)
 </programlisting>
    Although this query runs much faster than with either of the single
    indexes, we pay a penalty in index size.  Each of the single-column
-   btree indexes occupies 2 MB, so the total space needed is 12 MB,
-   eight times the space used by the bloom index.
+   btree indexes occupies 88.5 MB, so the total space needed is 531 MB,
+   over three times the space used by the bloom index.
   </para>
  </sect2>