Merge #339: checkpoint SQLite WAL outside request threads

config/database.yml

@@ -9,6 +9,11 @@ default: &default
   pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 10 } %>
   timeout: 5000
   default_transaction_mode: immediate
+  # Checkpoint on a background connection instead (SqliteWalCheckpoint).
+  # Non-test processes start a contender; forking servers stop before fork and
+  # start again in the child so the flock is never inherited.
+  pragmas:
+    wal_autocheckpoint: 0
 
 development:
   primary:

config/initializers/sqlite_wal_checkpoint.rb

@@ -0,0 +1,8 @@
+# Loaded from lib/rails_ext (autoload_lib ignore list) so reloads do not orphan
+# the contender thread. Non-test processes start here; Puma/Resque stop before
+# fork and start again in the child.
+require Rails.root.join("lib/rails_ext/sqlite_wal_checkpoint")
+
+Rails.application.config.after_initialize do
+  SqliteWalCheckpoint.start unless Rails.env.test?
+end

config/puma.rb

@@ -50,6 +50,12 @@ plugin :tmp_restart
 # Reset all membership connections
 Membership.disconnect_all
 
+# Initializer starts a contender in this process. Stop before fork so workers
+# do not inherit the flock; each worker starts its own contender. Single-process
+# mode never forks, so the initializer's contender keeps running.
+before_fork { SqliteWalCheckpoint.stop }
+before_worker_boot { SqliteWalCheckpoint.start }
+
 Signal.trap :SIGPROF do
   Thread.list.each do |t|
     puts t