doc: Reword unexplained abbreviation

The previous wording used MVF to indicate the Most Common Values'
Frequencies, but the abbreviation was never explained or defined.
Reword to mcv_freqs to make the use clearer.

Also add MCF and MCV as acronyms as they were using 
markup but were missing from the acronyms page.

Reported-by: Eric Mutta 
Reviewed-by: Tom Lane 
Discussion: https://postgr.es/m/166112292492.654.5377188452604176150@wrigleys.postgresql.org

diff --git a/doc/src/sgml/acronyms.sgml b/doc/src/sgml/acronyms.sgml
index 2df6559accce57af2304f4a4cbef4b711c390275..a60ff54a6ce1c8b4d7f31664887d6146fe2ee8c0 100644 (file)
--- a/doc/src/sgml/acronyms.sgml
+++ b/doc/src/sgml/acronyms.sgml
@@ -408,6 +408,26 @@
     
    
 
+   
+    MCF
+    
+     
+      Most Common Frequency, that is the frequency associated with some
+      Most Common Value
+     
+    
+   
+
+   
+    MCV
+    
+     
+      Most Common Value, one of the values appearing most often within a
+      particular table column
+     
+    
+   
+
    
     MITM
     

diff --git a/doc/src/sgml/planstats.sgml b/doc/src/sgml/planstats.sgml
index df85ea5eea48c07be23c6bbf33916cac2ebf8db0..d2b84b301f5c6c9af4584774c7d18d9206b2848c 100644 (file)
--- a/doc/src/sgml/planstats.sgml
+++ b/doc/src/sgml/planstats.sgml
@@ -203,7 +203,7 @@ EXPLAIN SELECT * FROM tenk1 WHERE stringu1 = 'xxx';
    MCVs:
 
 
-selectivity = (1 - sum(mvf))/(num_distinct - num_mcv)
+selectivity = (1 - sum(mcv_freqs))/(num_distinct - num_mcv)
             = (1 - (0.00333333 + 0.003 + 0.003 + 0.003 + 0.003 + 0.003 +
                     0.003 + 0.003 + 0.003 + 0.003))/(676 - 10)
             = 0.0014559