From 67fd8674c3ead2578d58d2d1f4e6c0879bb91c70 Mon Sep 17 00:00:00 2001
From: Andy Atkinson <andyatkinson@gmail.com>
Date: Wed, 3 Jan 2024 15:33:23 -0600
Subject: [PATCH] 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    | 10 ++++++++++
 app/views/pg_hero/home/index.html.erb |  4 ++++
 app/views/pg_hero/home/space.html.erb |  3 +++
 lib/pghero/methods/basic.rb           |  4 ++++
 4 files changed, 21 insertions(+)

diff --git a/app/helpers/pg_hero/home_helper.rb b/app/helpers/pg_hero/home_helper.rb
index 6caa2d4c4..afb40aedd 100644
--- a/app/helpers/pg_hero/home_helper.rb
+++ b/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
 
diff --git a/app/views/pg_hero/home/index.html.erb b/app/views/pg_hero/home/index.html.erb
index dfb80ef11..7e7001aec 100644
--- a/app/views/pg_hero/home/index.html.erb
+++ b/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>
diff --git a/app/views/pg_hero/home/space.html.erb b/app/views/pg_hero/home/space.html.erb
index 0376b291b..c74fbe9ab 100644
--- a/app/views/pg_hero/home/space.html.erb
+++ b/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>
diff --git a/lib/pghero/methods/basic.rb b/lib/pghero/methods/basic.rb
index a17bca635..302a5f456 100644
--- a/lib/pghero/methods/basic.rb
+++ b/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: [])