GUC: adjust effective_cache_size docs and SQL description

Clarify that effective_cache_size is both kernel buffers and shared
buffers.

Reported-by: nat@makarevitch.org
Discussion: https://postgr.es/m/153685164808.22334.15432535018443165207@wrigleys.postgresql.org

Backpatch-through: 9.3

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index b78603b0c7114c2ff75f862e580a9740070b718f..103942cf267ff15b5b638efbda78fba29e81587b 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3426,7 +3426,8 @@ include_dir 'conf.d'
         used. When setting this parameter you should consider both
         <productname>PostgreSQL</productname>'s shared buffers and the
         portion of the kernel's disk cache that will be used for
-        <productname>PostgreSQL</productname> data files.  Also, take
+        <productname>PostgreSQL</productname> data files, though some
+        data might exist in both places. Also, take
         into account the expected number of concurrent queries on different
         tables, since they will have to share the available
         space.  This parameter has no effect on the size of shared

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 0db8abde0519a9953b04ad221429386777c00ba2..8b845105f8ed02f379941b121dcf36ef968d55ec 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2614,10 +2614,9 @@ static struct config_int ConfigureNamesInt[] =
 
    {
        {"effective_cache_size", PGC_USERSET, QUERY_TUNING_COST,
-           gettext_noop("Sets the planner's assumption about the size of the disk cache."),
-           gettext_noop("That is, the portion of the kernel's disk cache that "
-                        "will be used for PostgreSQL data files. This is measured in disk "
-                        "pages, which are normally 8 kB each."),
+           gettext_noop("Sets the planner's assumption about the size of the data cache."),
+           gettext_noop("That is, the size of the cache used for PostgreSQL data files. "
+                        "This is measured in disk pages, which are normally 8 kB each."),
            GUC_UNIT_BLOCKS,
        },
        &effective_cache_size,