contrib/bloom documentation improvement

This commit documents rounding of "length" parameter and absence of support
for unique indexes and NULLs searching.  Backpatch to 9.6 where contrib/bloom
was introduced.

Discussion: https://postgr.es/m/CAF4Au4wPQQ7EHVSnzcLjsbY3oLSzVk6UemZLD1Sbmwysy3R61g%40mail.gmail.com
Author: Oleg Bartunov with minor editorialization by me
Backpatch-through: 9.6

diff --git a/doc/src/sgml/bloom.sgml b/doc/src/sgml/bloom.sgml
index f857b09bd6ba5638bf0ec35472712821902d7b79..1f671ed919656a902e19cf7946d3127a9c622106 100644 (file)
--- a/doc/src/sgml/bloom.sgml
+++ b/doc/src/sgml/bloom.sgml
@@ -51,8 +51,8 @@
     length
     
      
-      Length of each signature (index entry) in bits. The default
-      is 80 bits and maximum is 4096.
+      Length of each signature (index entry) in bits, it is rounded up to the nearest
+      multiple of 16. The default is 80 bits and maximum is 4096.
      
     
    
@@ -242,6 +242,20 @@ DEFAULT FOR TYPE text USING bloom AS
       operations in the future.
      
     
+
+    
+     
+       bloom access method doesn't support
+       UNIQUE indexes.
+     
+    
+
+    
+     
+       bloom access method doesn't support searching for
+       NULL values.
+     
+