Increase the default value of effective_cache_size to 4GB.

Per discussion, the old value of 128MB is ridiculously small on modern
machines; in fact, it's not even any larger than the default value of
shared_buffers, which it certainly should be.  Increase to 4GB, which
is unlikely to be any worse than the old default for anyone, and should
be noticeably better for most.  Eventually we might have an autotuning
scheme for this setting, but the recent attempt crashed and burned,
so for now just do this.

doc/src/sgml/config.sgml

@@ -3194,8 +3194,8 @@ include 'filename'
         memory allocated by <productname>PostgreSQL</productname>, nor
         does it reserve kernel disk cache; it is used only for estimation
         purposes.  The system also does not assume data remains in
-        the disk cache between queries.  The default is 128 megabytes
-        (<literal>128MB</>).
+        the disk cache between queries.  The default is 4 gigabytes
+        (<literal>4GB</>).
        </para>
       </listitem>
      </varlistentry>

doc/src/sgml/release-9.4.sgml

@@ -720,20 +720,12 @@
        </para>
       </listitem>
 
-      <listitem>
-       <para>
-        Auto-tune <link
-        linkend="guc-effective-cache-size"><varname>effective_cache_size</></link>
-        to be four-times shared buffers (Bruce Momjian, Tom Lane)
-       </para>
-      </listitem>
-
       <listitem>
        <para>
         Increase <link
         linkend="guc-work-mem"><varname>work_mem</></link> and <link
         linkend="guc-maintenance-work-mem"><varname>maintenance_work_mem</></link>
-        defaults by four-times (Bruce Momjian)
+        defaults by four times (Bruce Momjian)
        </para>
 
        <para>
@@ -741,6 +733,14 @@
        </para>
       </listitem>
 
+      <listitem>
+       <para>
+        Increase the default setting of <link
+        linkend="guc-effective-cache-size"><varname>effective_cache_size</></link>
+        to 4GB (Bruce Momjian, Tom Lane)
+       </para>
+      </listitem>
+
       <listitem>
        <para>
         Allow terabyte units to be specified for configuration variable

src/backend/utils/misc/postgresql.conf.sample

@@ -283,7 +283,7 @@
 #cpu_tuple_cost = 0.01			# same scale as above
 #cpu_index_tuple_cost = 0.005		# same scale as above
 #cpu_operator_cost = 0.0025		# same scale as above
-#effective_cache_size = 128MB
+#effective_cache_size = 4GB
 
 # - Genetic Query Optimizer -
 

src/include/optimizer/cost.h

@@ -27,7 +27,7 @@
 #define DEFAULT_CPU_INDEX_TUPLE_COST 0.005
 #define DEFAULT_CPU_OPERATOR_COST  0.0025
 
-#define DEFAULT_EFFECTIVE_CACHE_SIZE  16384		/* measured in pages */
+#define DEFAULT_EFFECTIVE_CACHE_SIZE  524288	/* measured in pages */
 
 typedef enum
 {