From 248a8da2f6c35fc62d97b0842902af182814e25c Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Fri, 10 Apr 2009 03:13:36 +0000
Subject: [PATCH] Document how *_blks_read statistics columns are computed.

---
 doc/src/sgml/monitoring.sgml | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 9dfc0578d4..4b0c4999cd 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -927,8 +927,9 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
      <function>pg_stat_get_blocks_fetched</function> minus
      <function>pg_stat_get_blocks_hit</function> gives the number of kernel
      <function>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 <literal>*_blks_read</>
+     statistics columns uses this subtraction, i.e. fetched minus hit.
     </para>
    </note>
 
-- 
2.39.5