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 e6bbe8af9836786c6e5cba36bb8b4a0750d1d8f2..5189e8e26ceeac40e6bcac1a9655e783581f4beb 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3760,7 +3760,8 @@ 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 f33160bf69c2b40c041d426a03969ac21e11f3ea..d0d3903f201f1f72dd46943d9bdee4cf27f3cb59 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2738,10 +2738,9 @@ 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,