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 7554cba3f96ba12d728095a0ec4625de47e16a98..b8e32d765bd1f70d767c278cbdde83ab3b8569f5 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4147,7 +4147,8 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
         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 2317e8be6be6b287bf160edabe9145d513d16964..e471d7f53cdbb77500944f6a62c9ac7da57e9d56 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2987,10 +2987,9 @@ 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,