Run Solid Queue in async mode on Render free tier (#23)

* Run Solid Queue in async mode on Render free tier

Companion to #22 (WEB_CONCURRENCY=0). Free tier (512MB) can't fit
SQ's default fork mode, which spawns supervisor + worker +
dispatcher + scheduler subprocesses for ~460MB of RSS overhead on
top of Puma. The container OOM-cycles every ~7-15 min — the deploy
still looks "live" but HTTP returns 502s during each restart
window.

`solid_queue_mode :async` (documented switch in
lib/puma/plugin/solid_queue.rb of the gem) tells the plugin to
run worker/dispatcher/scheduler as threads inside the Puma master
process. The 4 SQ subprocesses collapse into ~50MB of thread
overhead in Puma. Container RSS drops from ~530MB (cycling into
OOM) to a flat ~300MB.

Trade-off per SQ's own docs ("Only use async if you know what
you're doing and have strong reasons to"):
- Less isolation between SQ and Puma. A leaky/hung SQ thread
  affects request serving. For low-traffic student projects this
  is the right call; revisit if upgrading to a paid plan.
- No inter-process parallelism for jobs. Free tier is already
  0.1 vCPU, so this isn't real lost throughput.
- Recurring tasks and concurrency controls still work unchanged.

The DB pool bump (5 → 8) is non-optional: previously the pool was
sized for Puma's 3 request threads only; now the same process
also runs 3 SQ worker threads + dispatcher + scheduler. Under any
load the old pool=5 would throw ConnectionTimeoutError. The 5 ->
8 default still respects DB_POOL env override for projects that
need finer control.

Diagnosed and validated on raghubetina/aplace:
raghubetina/aplace#58 — RSS metric showed
the predicted plateau at ~300MB with zero growth after deploy.

* Pin solid_queue ~> 1.3 for solid_queue_mode :async support

This branch's puma.rb adds `solid_queue_mode :async if ENV["SOLID_QUEUE_IN_PUMA"]`,
but the lockfile resolved to solid_queue 1.1.4, which has no such DSL method.
Booting in production crashes immediately with:

  config/puma.rb:47:in 'Puma::DSL#_load_from': undefined method
  'solid_queue_mode' for an instance of Puma::DSL (NoMethodError)

Async supervisor mode was re-introduced in solid_queue 1.3.0
(rails/solid_queue#644); the earlier 0.4 implementation was
removed in 0.7. Pinning to ~> 1.3 documents the minimum that
matches this branch's puma.rb and updates the lockfile to 1.4.0.

Caught by deploying a marketplace smoke-test app built from this
branch + #22 + #24 to Render free tier.

Author: raghubetina

Gemfile

@@ -8,7 +8,7 @@ gem "importmap-rails"                 # JavaScript with ESM import maps
 gem "turbo-rails"                     # Hotwire page acceleration (SPA-like)
 gem "stimulus-rails"                  # Hotwire JavaScript framework
 gem "solid_cache"                     # Database-backed Rails.cache
-gem "solid_queue"                     # Database-backed Active Job
+gem "solid_queue", "~> 1.3"           # Database-backed Active Job — 1.3+ required for solid_queue_mode :async in config/puma.rb
 gem "solid_cable"                     # Database-backed Action Cable
 gem "bootsnap", require: false        # Faster boot times via caching
 gem "thruster", require: false        # HTTP caching/compression for Puma

Gemfile.lock

@@ -86,7 +86,7 @@ GEM
       erubi (>= 1.0.0)
       rack (>= 0.9.0)
       rouge (>= 1.0.0)
-    bigdecimal (4.1.0)
+    bigdecimal (4.1.2)
     bindex (0.8.1)
     binding_of_caller (2.0.0)
       debug_inspector (>= 1.2.0)
@@ -131,8 +131,9 @@ GEM
       devise
       indefinite_article
     drb (2.2.3)
+    erb (6.0.4)
     erubi (1.13.1)
-    et-orbi (1.2.11)
+    et-orbi (1.4.0)
       tzinfo
     faraday (2.12.2)
       faraday-net_http (>= 2.0, < 3.5)
@@ -154,10 +155,10 @@ GEM
     ffi-compiler (1.3.2)
       ffi (>= 1.15.5)
       rake
-    fugit (1.11.1)
-      et-orbi (~> 1, >= 1.2.11)
+    fugit (1.12.1)
+      et-orbi (~> 1.4)
       raabro (~> 1.4)
-    globalid (1.2.1)
+    globalid (1.3.0)
       activesupport (>= 6.1)
     grade_runner (0.0.16)
       activesupport (>= 2.3.5)
@@ -188,8 +189,9 @@ GEM
     indefinite_article (0.2.5)
       activesupport
     io-console (0.8.2)
-    irb (1.15.1)
+    irb (1.18.0)
       pp (>= 0.6.0)
+      prism (>= 1.3.0)
       rdoc (>= 4.0.0)
       reline (>= 0.4.2)
     json (2.19.3)
@@ -211,7 +213,7 @@ GEM
       ffi-compiler (~> 1.0)
       rake (~> 13.0)
     logger (1.7.0)
-    loofah (2.24.0)
+    loofah (2.25.1)
       crass (~> 1.0.2)
       nokogiri (>= 1.12.0)
     mail (2.8.1)
@@ -223,8 +225,7 @@ GEM
     matrix (0.4.2)
     method_source (1.1.0)
     mini_mime (1.1.5)
-    mini_portile2 (2.8.9)
-    minitest (6.0.2)
+    minitest (6.0.6)
       drb (~> 2.0)
       prism (~> 1.5)
     msgpack (1.8.0)
@@ -240,24 +241,21 @@ GEM
     net-smtp (0.5.1)
       net-protocol
     nio4r (2.7.4)
-    nokogiri (1.18.4)
-      mini_portile2 (~> 2.8.2)
+    nokogiri (1.19.3-aarch64-linux-gnu)
       racc (~> 1.4)
-    nokogiri (1.18.4-aarch64-linux-gnu)
+    nokogiri (1.19.3-aarch64-linux-musl)
       racc (~> 1.4)
-    nokogiri (1.18.4-aarch64-linux-musl)
+    nokogiri (1.19.3-arm-linux-gnu)
       racc (~> 1.4)
-    nokogiri (1.18.4-arm-linux-gnu)
+    nokogiri (1.19.3-arm-linux-musl)
       racc (~> 1.4)
-    nokogiri (1.18.4-arm-linux-musl)
+    nokogiri (1.19.3-arm64-darwin)
       racc (~> 1.4)
-    nokogiri (1.18.4-arm64-darwin)
+    nokogiri (1.19.3-x86_64-darwin)
       racc (~> 1.4)
-    nokogiri (1.18.4-x86_64-darwin)
+    nokogiri (1.19.3-x86_64-linux-gnu)
       racc (~> 1.4)
-    nokogiri (1.18.4-x86_64-linux-gnu)
-      racc (~> 1.4)
-    nokogiri (1.18.4-x86_64-linux-musl)
+    nokogiri (1.19.3-x86_64-linux-musl)
       racc (~> 1.4)
     octokit (5.6.1)
       faraday (>= 1, < 3)
@@ -293,13 +291,13 @@ GEM
       nio4r (~> 2.0)
     raabro (1.4.0)
     racc (1.8.1)
-    rack (3.2.5)
-    rack-session (2.1.0)
+    rack (3.2.6)
+    rack-session (2.1.2)
       base64 (>= 0.1.0)
       rack (>= 3.0.0)
     rack-test (2.2.0)
       rack (>= 1.3)
-    rackup (2.2.1)
+    rackup (2.3.1)
       rack (>= 3)
     rails (8.0.2)
       actioncable (= 8.0.2)
@@ -319,12 +317,12 @@ GEM
       actionpack (>= 5.0.1.rc1)
       actionview (>= 5.0.1.rc1)
       activesupport (>= 5.0.1.rc1)
-    rails-dom-testing (2.2.0)
+    rails-dom-testing (2.3.0)
       activesupport (>= 5.0.0)
       minitest
       nokogiri (>= 1.6)
-    rails-html-sanitizer (1.6.2)
-      loofah (~> 2.21)
+    rails-html-sanitizer (1.7.0)
+      loofah (~> 2.25)
       nokogiri (>= 1.15.7, != 1.16.7, != 1.16.6, != 1.16.5, != 1.16.4, != 1.16.3, != 1.16.2, != 1.16.1, != 1.16.0.rc1, != 1.16.0)
     rails_db (2.5.0)
       activerecord
@@ -343,15 +341,17 @@ GEM
       thor (~> 1.0, >= 1.2.2)
       zeitwerk (~> 2.6)
     rainbow (3.1.1)
-    rake (13.3.1)
+    rake (13.4.2)
     ransack (4.3.0)
       activerecord (>= 6.1.5)
       activesupport (>= 6.1.5)
       i18n
-    rdoc (6.12.0)
+    rdoc (7.2.0)
+      erb
       psych (>= 4.0.0)
+      tsort
     regexp_parser (2.11.3)
-    reline (0.6.0)
+    reline (0.6.3)
       io-console (~> 0.5)
     responders (3.1.1)
       actionpack (>= 5.2)
@@ -438,13 +438,13 @@ GEM
       activejob (>= 7.2)
       activerecord (>= 7.2)
       railties (>= 7.2)
-    solid_queue (1.1.4)
+    solid_queue (1.4.0)
       activejob (>= 7.1)
       activerecord (>= 7.1)
       concurrent-ruby (>= 1.3.1)
-      fugit (~> 1.11.0)
+      fugit (~> 1.11)
       railties (>= 7.1)
-      thor (~> 1.3.1)
+      thor (>= 1.3.1)
     stimulus-rails (1.3.4)
       railties (>= 6.0.0)
     stringio (3.2.0)
@@ -453,7 +453,7 @@ GEM
       unicode-display_width (~> 3.0)
     terminal-table (4.0.0)
       unicode-display_width (>= 1.1.1, < 4)
-    thor (1.3.2)
+    thor (1.5.0)
     thruster (0.1.12)
     thruster (0.1.12-aarch64-linux)
     thruster (0.1.12-arm64-darwin)
@@ -490,7 +490,7 @@ GEM
     websocket-extensions (0.1.5)
     xpath (3.2.0)
       nokogiri (~> 1.8)
-    zeitwerk (2.7.2)
+    zeitwerk (2.8.0)
     zip (2.0.2)
 
 PLATFORMS
@@ -541,7 +541,7 @@ DEPENDENCIES
   shoulda-matchers (~> 7.0)
   solid_cable
   solid_cache
-  solid_queue
+  solid_queue (~> 1.3)
   stimulus-rails
   thruster
   tsort

config/database.yml

@@ -17,7 +17,12 @@ default: &default
   encoding: unicode
   # For details on connection pooling, see Rails configuration guide
   # https://guides.rubyonrails.org/configuring.html#database-pooling
-  pool: <%= ENV.fetch("DB_POOL") { 5 } %>
+  #
+  # Sized for Puma's 3 request threads + Solid Queue's async-mode threads
+  # (3 worker + dispatcher + scheduler) sharing this pool. The previous
+  # default of 5 was right at the edge and produced ConnectionTimeoutError
+  # under any load once SQ threads moved into the Puma process.
+  pool: <%= ENV.fetch("DB_POOL") { 8 } %>
 
 
 development:

config/puma.rb

@@ -36,6 +36,16 @@
 # Run the Solid Queue supervisor inside of Puma for single-server deployments
 plugin :solid_queue if ENV["SOLID_QUEUE_IN_PUMA"]
 
+# Run Solid Queue in async mode: worker/dispatcher/scheduler run as threads
+# inside the Puma master process instead of being forked into 4 subprocesses.
+# Required on Render's 512MB free plan — fork mode adds ~460MB of process
+# overhead (supervisor + 3 children) and pushes the container into OOM-loop.
+# Async mode collapses that to ~50MB of additional thread overhead in Puma
+# master. Trade-off: less isolation between SQ threads and Puma — a hung or
+# leaky SQ thread affects request serving. For low-traffic student projects
+# the trade-off is right; revisit if upgrading to a paid plan with more RAM.
+solid_queue_mode :async if ENV["SOLID_QUEUE_IN_PUMA"]
+
 # Specify the PID file. Defaults to tmp/pids/server.pid in development.
 # In other environments, only set the PID file if requested.
 pidfile ENV["PIDFILE"] if ENV["PIDFILE"]