tune SQLite PRAGMAs for production

Add journal_size_limit (64MB), default_transaction_mode: :immediate,
and mmap_size (128MB) across dev, test, and prod configs. Benchmarks
showed IMMEDIATE mode eliminates transaction upgrade BUSY errors and
mmap improves read throughput.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

config/dev.exs

@@ -6,6 +6,9 @@ config :berrypod, Berrypod.Repo,
   pool_size: 5,
   journal_mode: :wal,
   busy_timeout: 5000,
+  journal_size_limit: 67_108_864,
+  default_transaction_mode: :immediate,
+  custom_pragmas: [mmap_size: 134_217_728],
   stacktrace: true,
   show_sensitive_data_on_connection_error: true
 

config/runtime.exs

@@ -32,7 +32,10 @@ if config_env() == :prod do
     database: database_path,
     pool_size: String.to_integer(System.get_env("POOL_SIZE") || "5"),
     journal_mode: :wal,
-    busy_timeout: 5000
+    busy_timeout: 5000,
+    journal_size_limit: 67_108_864,
+    default_transaction_mode: :immediate,
+    custom_pragmas: [mmap_size: 134_217_728]
 
   # The secret key base is used to sign/encrypt cookies and other secrets.
   # A default value is used in config/dev.exs and config/test.exs but you

config/test.exs

@@ -15,7 +15,10 @@ config :berrypod, Berrypod.Repo,
   journal_mode: :wal,
   busy_timeout: 15_000,
   queue_target: 5_000,
-  queue_interval: 10_000
+  queue_interval: 10_000,
+  journal_size_limit: 67_108_864,
+  default_transaction_mode: :immediate,
+  custom_pragmas: [mmap_size: 134_217_728]
 
 # We don't run a server during test. If one is required,
 # you can enable the server option below.