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 c7c90d20e8eea84c7cc26b7ab62d363bc1bb6bd1..f6a7bd538388788a19b5e5f2790903aa667d8f2a 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3962,7 +3962,8 @@ 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 e71300b5e2732b41859cb77e78ded0bf6e65130f..ba9ad291b8cb1659d5dfee566b1bddbf876c694f 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2803,10 +2803,9 @@ 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,