let the connection pool of new applications have size 1 rather than 5

The majority of Rails applications are multiprocess, people
may wonder why rails new generates a default pool of 5, does
my application need a connection pool of 5? By generating
a default of 1 database.yml is much more clear, and with
the comment people know what is the connection pool for,
and they know it has to be bigger for multithread apps.

railties/guides/code/getting_started/config/database.yml

@@ -6,7 +6,9 @@
 development:
   adapter: sqlite3
   database: db/development.sqlite3
-  pool: 5
+  # Maximum number of database connections available per process. Please
+  # increase this number in multithreaded applications.
+  pool: 1
   timeout: 5000
 
 # Warning: The database defined as "test" will be erased and
@@ -15,11 +17,15 @@ development:
 test:
   adapter: sqlite3
   database: db/test.sqlite3
-  pool: 5
+  # Maximum number of database connections available per process. Please
+  # increase this number in multithreaded applications.
+  pool: 1
   timeout: 5000
 
 production:
   adapter: sqlite3
   database: db/production.sqlite3
-  pool: 5
+  # Maximum number of database connections available per process. Please
+  # increase this number in multithreaded applications.
+  pool: 1
   timeout: 5000

railties/lib/rails/generators/rails/app/templates/config/databases/mysql.yml

@@ -12,7 +12,9 @@ development:
   adapter: mysql2
   encoding: utf8
   database: <%= app_name %>_development
-  pool: 5
+  # Maximum number of database connections available per process. Please
+  # increase this number in multithreaded applications.
+  pool: 1
   username: root
   password:
 <% if mysql_socket -%>
@@ -28,7 +30,9 @@ test:
   adapter: mysql2
   encoding: utf8
   database: <%= app_name %>_test
-  pool: 5
+  # Maximum number of database connections available per process. Please
+  # increase this number in multithreaded applications.
+  pool: 1
   username: root
   password:
 <% if mysql_socket -%>
@@ -41,7 +45,9 @@ production:
   adapter: mysql2
   encoding: utf8
   database: <%= app_name %>_production
-  pool: 5
+  # Maximum number of database connections available per process. Please
+  # increase this number in multithreaded applications.
+  pool: 1
   username: root
   password:
 <% if mysql_socket -%>

railties/lib/rails/generators/rails/app/templates/config/databases/postgresql.yml

@@ -16,7 +16,9 @@ development:
   adapter: postgresql
   encoding: unicode
   database: <%= app_name %>_development
-  pool: 5
+  # Maximum number of database connections available per process. Please
+  # increase this number in multithreaded applications.
+  pool: 1
   username: <%= app_name %>
   password:
 
@@ -42,7 +44,9 @@ test:
   adapter: postgresql
   encoding: unicode
   database: <%= app_name %>_test
-  pool: 5
+  # Maximum number of database connections available per process. Please
+  # increase this number in multithreaded applications.
+  pool: 1
   username: <%= app_name %>
   password:
 
@@ -50,6 +54,8 @@ production:
   adapter: postgresql
   encoding: unicode
   database: <%= app_name %>_production
-  pool: 5
+  # Maximum number of database connections available per process. Please
+  # increase this number in multithreaded applications.
+  pool: 1
   username: <%= app_name %>
   password:

railties/lib/rails/generators/rails/app/templates/config/databases/sqlite3.yml

@@ -6,7 +6,9 @@
 development:
   adapter: sqlite3
   database: db/development.sqlite3
-  pool: 5
+  # Maximum number of database connections available per process. Please
+  # increase this number in multithreaded applications.
+  pool: 1
   timeout: 5000
 
 # Warning: The database defined as "test" will be erased and
@@ -15,11 +17,15 @@ development:
 test:
   adapter: sqlite3
   database: db/test.sqlite3
-  pool: 5
+  # Maximum number of database connections available per process. Please
+  # increase this number in multithreaded applications.
+  pool: 1
   timeout: 5000
 
 production:
   adapter: sqlite3
   database: db/production.sqlite3
-  pool: 5
+  # Maximum number of database connections available per process. Please
+  # increase this number in multithreaded applications.
+  pool: 1
   timeout: 5000