DEV: remove exec_sql and replace with mini_sql

Introduce new patterns for direct sql that are safe and fast.

MiniSql is not prone to memory bloat that can happen with direct PG usage.
It also has an extremely fast materializer and very a convenient API

- DB.exec(sql, *params) => runs sql returns row count
- DB.query(sql, *params) => runs sql returns usable objects (not a hash)
- DB.query_hash(sql, *params) => runs sql returns an array of hashes
- DB.query_single(sql, *params) => runs sql and returns a flat one dimensional array
- DB.build(sql) => returns a sql builder

See more at: https://github.com/discourse/mini_sql

lib/tasks/import.rake

@@ -29,7 +29,7 @@ MS_SPEND_CREATING_POST ||= 5000
 def insert_post_timings
   log "Inserting post timings..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     INSERT INTO post_timings (topic_id, post_number, user_id, msecs)
          SELECT topic_id, post_number, user_id, #{MS_SPEND_CREATING_POST}
            FROM posts
@@ -41,7 +41,7 @@ end
 def insert_post_replies
   log "Inserting post replies..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     INSERT INTO post_replies (post_id, reply_id, created_at, updated_at)
          SELECT p2.id, p.id, p.created_at, p.created_at
            FROM posts p
@@ -53,7 +53,7 @@ end
 def insert_topic_users
   log "Inserting topic users..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     INSERT INTO topic_users (user_id, topic_id, posted, last_read_post_number, highest_seen_post_number, first_visited_at, last_visited_at, total_msecs_viewed)
          SELECT user_id, topic_id, 't' , MAX(post_number), MAX(post_number), MIN(created_at), MAX(created_at), COUNT(id) * #{MS_SPEND_CREATING_POST}
            FROM posts
@@ -66,7 +66,7 @@ end
 def insert_topic_views
   log "Inserting topic views..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     WITH X AS (
           SELECT topic_id, user_id, DATE(p.created_at) posted_at
             FROM posts p
@@ -86,7 +86,7 @@ end
 def insert_user_actions
   log "Inserting user actions for NEW_TOPIC = 4..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     INSERT INTO user_actions (action_type, user_id, target_topic_id, target_post_id, acting_user_id, created_at, updated_at)
          SELECT 4, p.user_id, topic_id, p.id, p.user_id, p.created_at, p.created_at
            FROM posts p
@@ -100,7 +100,7 @@ def insert_user_actions
 
   log "Inserting user actions for REPLY = 5..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     INSERT INTO user_actions (action_type, user_id, target_topic_id, target_post_id, acting_user_id, created_at, updated_at)
          SELECT 5, p.user_id, topic_id, p.id, p.user_id, p.created_at, p.created_at
            FROM posts p
@@ -114,7 +114,7 @@ def insert_user_actions
 
   log "Inserting user actions for RESPONSE = 6..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     INSERT INTO user_actions (action_type, user_id, target_topic_id, target_post_id, acting_user_id, created_at, updated_at)
          SELECT 6, p.user_id, p.topic_id, p.id, p2.user_id, p.created_at, p.created_at
            FROM posts p
@@ -137,7 +137,7 @@ end
 def insert_user_options
   log "Inserting user options..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     INSERT INTO user_options (
                   user_id,
                   email_always,
@@ -189,7 +189,7 @@ end
 def insert_user_stats
   log "Inserting user stats..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     INSERT INTO user_stats (user_id, new_since)
          SELECT id, created_at
            FROM users
@@ -200,7 +200,7 @@ end
 def insert_user_visits
   log "Inserting user visits..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     INSERT INTO user_visits (user_id, visited_at, posts_read)
          SELECT user_id, DATE(created_at), COUNT(*)
            FROM posts
@@ -213,7 +213,7 @@ end
 def insert_draft_sequences
   log "Inserting draft sequences..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     INSERT INTO draft_sequences (user_id, draft_key, sequence)
          SELECT user_id, CONCAT('#{Draft::EXISTING_TOPIC}', id), 1
            FROM topics
@@ -226,7 +226,7 @@ end
 def update_user_stats
   log "Updating user stats..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     WITH X AS (
       SELECT p.user_id
            , COUNT(p.id) posts
@@ -283,7 +283,7 @@ end
 def update_posts
   log "Updating posts..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     WITH Y AS (
       SELECT post_id, COUNT(*) replies FROM post_replies GROUP BY post_id
     )
@@ -310,7 +310,7 @@ end
 def update_topics
   log "Updating topics..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     WITH X AS (
       SELECT topic_id
            , COUNT(*) posts
@@ -350,7 +350,7 @@ end
 def update_categories
   log "Updating categories..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     WITH X AS (
         SELECT category_id
              , MAX(p.id) post_id
@@ -382,7 +382,7 @@ end
 def update_users
   log "Updating users..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     WITH X AS (
         SELECT user_id
              , MIN(created_at) min_created_at
@@ -406,7 +406,7 @@ end
 def update_groups
   log "Updating groups..."
 
-  exec_sql <<-SQL
+  DB.exec <<-SQL
     WITH X AS (
         SELECT group_id, COUNT(*) count
           FROM group_users
@@ -428,12 +428,6 @@ def log(message)
   puts "[#{DateTime.now.strftime("%Y-%m-%d %H:%M:%S")}] #{message}"
 end
 
-def exec_sql(sql)
-  ActiveRecord::Base.transaction do
-    ActiveRecord::Base.exec_sql(sql)
-  end
-end
-
 task "import:create_phpbb_permalinks" => :environment do
   log 'Creating Permalinks...'
 
@@ -477,7 +471,6 @@ task "import:remap_old_phpbb_permalinks" => :environment do
       # skip
     end
   end
-  i
 
   log "Done! #{i} posts remapped."
 end