Use concurrently for remove_index

Present a explanation box recommending to use CONCURRENTLY with DROP
INDEX. In Active Record, this requires two things:
disable_ddl_transaction! once at the top of the migration file, and
"algorithm: :concurrently" option added to every remove_index line

Since this is a sensible default when PostgreSQL 14 or greater is in
use, since it can avoid downtime from an index drop, make it the
default.
Remove the ability to disable it since it seems unnecessary in
retrospect.

Only show the explanation box and only add the option to
remove_index when version 14 or greater is in use

app/helpers/pg_hero/home_helper.rb

@@ -16,6 +16,15 @@ def pghero_js_value(value)
       json_escape(value.to_json(root: false)).html_safe
     end
 
+    def pghero_drop_idx_concurrently_explanation
+      if @database.drop_idx_concurrently_supported?
+        ret =  "<h2>Tip: Use CONCURRENTLY for DROP INDEX</h2>"
+        ret << "<ul><li>Add <code>disable_ddl_transaction!</code> to your migration</li>"
+        ret << "<li>Add <code>algorithm: :concurrently</code> to each <code>remove_index</code></li></ul>"
+        ret.html_safe
+      end
+    end
+
     def pghero_remove_index(query)
       if query[:columns]
         columns = query[:columns].map(&:to_sym)
@@ -24,6 +33,7 @@ def pghero_remove_index(query)
       ret = String.new("remove_index #{query[:table].to_sym.inspect}")
       ret << ", name: #{(query[:name] || query[:index]).to_s.inspect}"
       ret << ", column: #{columns.inspect}" if columns
+      ret << ", algorithm: concurrently" if @database.drop_idx_concurrently_supported?
       ret
     end
 

app/views/pg_hero/home/index.html.erb

@@ -391,6 +391,10 @@
     <div id="migration2" style="display: none;">
       <pre>rails generate migration remove_unneeded_indexes</pre>
       <p>And paste</p>
+      <% if @database.drop_idx_concurrently_supported? %>
+        <p><%= pghero_drop_idx_concurrently_explanation %></p>
+      <% end %>
+      <p>And paste</p>
       <pre style="overflow: scroll; white-space: pre; word-break: normal;"><% @duplicate_indexes.each do |query| %>
 <%= pghero_remove_index(query[:unneeded_index]) %><% end %></pre>
     </div>

app/views/pg_hero/home/space.html.erb

@@ -31,6 +31,9 @@
 
     <div id="migration" style="display: none;">
       <pre>rails generate migration remove_unused_indexes</pre>
+      <% if @database.drop_idx_concurrently_supported? %>
+        <p><%= pghero_drop_idx_concurrently_explanation %></p>
+      <% end %>
       <p>And paste</p>
       <pre style="overflow: scroll; white-space: pre; word-break: normal;"><% @unused_indexes.sort_by { |q| [-q[:size_bytes], q[:index]] }.each do |query| %>
 <%= pghero_remove_index(query) %><% end %></pre>

lib/pghero/methods/basic.rb

@@ -34,6 +34,10 @@ def quote_ident(value)
         connection.quote_column_name(value)
       end
 
+      def drop_idx_concurrently_supported?
+        server_version_num >= 140000
+      end
+
       private
 
       def select_all(sql, conn: nil, query_columns: [])