GUC: adjust effective_cache_size docs and SQL description

Clarify that effective_cache_size is both kernel buffers and shared
buffers.

Reported-by: [email protected]
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 794d6c761b05151d3efbb113aad2209ffa056b59..64a6074e1c078e2232bf09fb34e2ae448baaf931 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3351,7 +3351,8 @@ include_dir 'conf.d'
         used. When setting this parameter you should consider both
         PostgreSQL's shared buffers and the
         portion of the kernel's disk cache that will be used for
-        PostgreSQL data files.  Also, take
+        PostgreSQL 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 787a3e0b13c06e78aebdd9e7986021aae77c28bd..b089b31ffd23f252d51437ea97a97d2c5bc1660e 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2486,10 +2486,9 @@ 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,