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 457029b0d4f3c5e6e69730733b5e3890ae719e20..347abbe4c9b5be46841d0e2a91faa6205e00b962 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4143,7 +4143,8 @@ 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 110ac0e57fbafc8b4d1e63bab5fe98ade22e2f15..cb0d1c54f6819e31037a54b2b3c8ab45e888ab63 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2979,10 +2979,9 @@ 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,