Document how *_blks_read statistics columns are computed.

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index acfccc4c997e788ceff43d7600ea0f52fb4b1dbe..8c4f2b7db1a7672821a908a3f3fd8af9d4625c16 100644 (file)
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -1,4 +1,4 @@
-
+
 
 
  Monitoring Database Activity
@@ -927,8 +927,9 @@ postgres: user database host 
      pg_stat_get_blocks_fetched minus
      pg_stat_get_blocks_hit gives the number of kernel
      read() calls issued for the table, index, or
-     database; but the actual number of physical reads is usually
-     lower due to kernel-level buffering.
+     database; the number of actual physical reads is usually
+     lower due to kernel-level buffering.  The *_blks_read
+     statistics columns uses this subtraction, i.e. fetched minus hit.