From 24cdea0a4ce25c00ac250d99333bd9cac984d61c Mon Sep 17 00:00:00 2001
From: Shane Handley <shanehandley@fastmail.com>
Date: Sat, 6 Jun 2020 18:26:48 +1000
Subject: [PATCH] Enable WAL and busy_timeout for each sqlite connection to
 mitigate db locks,

---
 .gitignore                    |  2 ++
 server/src/persistence/mod.rs | 24 +++++++++++++++++++++---
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/.gitignore b/.gitignore
index eb77a24e0d..2eaacda61e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -36,6 +36,8 @@ todo.txt
 # Game data
 *.sqlite
 *.sqlite-journal
+*.sqlite-wal
+*.sqlite-shm
 
 # direnv
 /.envrc
diff --git a/server/src/persistence/mod.rs b/server/src/persistence/mod.rs
index f4709a3edd..a47d253492 100644
--- a/server/src/persistence/mod.rs
+++ b/server/src/persistence/mod.rs
@@ -6,7 +6,7 @@ mod schema;
 
 extern crate diesel;
 
-use diesel::prelude::*;
+use diesel::{connection::SimpleConnection, prelude::*};
 use diesel_migrations::embed_migrations;
 use std::{env, fs, path::PathBuf};
 
@@ -24,8 +24,26 @@ pub fn run_migrations(db_dir: &str) -> Result<(), diesel_migrations::RunMigratio
 fn establish_connection(db_dir: &str) -> SqliteConnection {
     let db_dir = &apply_saves_dir_override(db_dir);
     let database_url = format!("{}/db.sqlite", db_dir);
-    SqliteConnection::establish(&database_url)
-        .unwrap_or_else(|_| panic!("Error connecting to {}", database_url))
+
+    let connection = SqliteConnection::establish(&database_url)
+        .unwrap_or_else(|_| panic!("Error connecting to {}", database_url));
+
+    // Use Write-Ahead-Logging for improved concurrency: https://sqlite.org/wal.html
+    // Set a busy timeout (in ms): https://sqlite.org/c3ref/busy_timeout.html
+    if let Err(error) = connection.batch_execute(
+        "
+        PRAGMA journal_mode = WAL;
+        PRAGMA busy_timeout = 250; 
+        ",
+    ) {
+        log::warn!(
+            "Failed adding PRAGMA statements while establishing sqlite connection, this will \
+             result in a higher likelihood of locking errors: {}",
+            error
+        );
+    }
+
+    connection
 }
 
 fn apply_saves_dir_override(db_dir: &str) -> String {