From ed2bbaa6b17f0e24e3c51dd0d3678832aa8eb1ef Mon Sep 17 00:00:00 2001
From: "Navy.gif" <navydotgif@gmail.com>
Date: Fri, 10 Feb 2023 23:57:34 +0200
Subject: [PATCH] retry certain queries (deadlocks)

---
 src/server/database/MariaDB.js | 85 ++++++++++++++++++++++------------
 1 file changed, 56 insertions(+), 29 deletions(-)

diff --git a/src/server/database/MariaDB.js b/src/server/database/MariaDB.js
index b9982cb..8b5607e 100644
--- a/src/server/database/MariaDB.js
+++ b/src/server/database/MariaDB.js
@@ -3,13 +3,15 @@ const mysql = require('mysql');
 const { inspect } = require('node:util');
 const { Util } = require('../../util');
 
+const SAFE_TO_RETRY = [ 'ER_LOCK_DEADLOCK' ];
+
 class MariaDB {
 
     constructor (server, config) {
 
-        if (!server) 
+        if (!server)
             Util.fatal(new Error('Missing reference to server!'));
-        if (!config) 
+        if (!config)
             Util.fatal(new Error('No config options provided!'));
 
         this.config = config;
@@ -19,7 +21,7 @@ class MariaDB {
         for (const host of hosts) {
             this._credentials.push({ host, user, port, password, database });
         }
-        
+
         this.pool = null;
         this.ready = false;
         this.debug = true;
@@ -37,11 +39,10 @@ class MariaDB {
         this.logger.status(`Creating${this._cluster ? ' cluster' : ''} connection pool`);
         if (this._cluster) {
             this.pool = mysql.createPoolCluster(this.config.options.cluster);
-            for (const creds of this._credentials) 
+            for (const creds of this._credentials)
                 this.pool.add({ ...this.config.options.client, ...creds });
-            
         } else {
-            this.pool = mysql.createPool({ ...this.config.options.client, ...this._credentials[0] }); 
+            this.pool = mysql.createPool({ ...this.config.options.client, ...this._credentials[0] });
         }
 
         this.pool.on('connection', (connection) => {
@@ -59,17 +60,17 @@ class MariaDB {
 
         this.pool.on('release', (connection) => {
             this.activeQueries--;
-            
-            if (!this.ready && !this.activeQueries && this.afterLastQuery) 
+
+            if (!this.ready && !this.activeQueries && this.afterLastQuery)
                 this.afterLastQuery();
-            
+
             this.logger.debug(`Connection released: ${connection?.threadId || null}`);
         });
 
         this.logger.info(`Testing MariaDB connection`);
         await new Promise((resolve, reject) => {
             this.pool.getConnection((err, conn) => {
-                if (err) 
+                if (err)
                     return reject(err);
                 conn.release();
                 return resolve();
@@ -106,30 +107,56 @@ class MariaDB {
 
     }
 
-    query (query, values) {
-
+    getConnection () {
         return new Promise((resolve, reject) => {
-
-            if (!this.ready) 
-                return reject(new Error('MariaDB not ready'));
-
-            let batch = false;
-            if (values && typeof values.some === 'function') 
-                batch = values.some(val => val instanceof Array);
-            this.logger.debug(`Incoming query (batch: ${batch})\n${query}\n${inspect(values)}`);
-
-            // If connected to a cluster, pick one of the node connection pools
-            // By default the config is set to use round robin for picking a pool when connected to a cluster
-            const pool = this._cluster ? this.pool.of('*') : this.pool;
-
-            return pool.query(query, values, (err, results, fields) => {
+            this.pool.getConnection((err, conn) => {
                 if (err) 
                     return reject(err);
-                if (results) 
-                    return resolve(results);
-                resolve(fields);
+                resolve(conn);
             });
         });
+    }
+
+    /** 
+     * Retry certain queries that are safe to retry, e.g. deadlock
+     * 
+     * @private 
+     * */
+    async #_query (query, values, attempts = 0) {
+        const connection = await this.getConnection();
+        try {
+            const result = await new Promise((resolve, reject) => {
+                const q = connection.query(query, values, (err, results, fields) => {
+                    if (err) 
+                        reject(err);
+                    else if (results) 
+                        resolve(results);
+                    else 
+                        resolve(fields);
+                    connection.release();
+                });
+                this.logger.debug(`Constructed query: ${q.sql}`);
+            });
+            return Promise.resolve(result);
+        } catch (err) {
+            // Retry safe errors 
+            if (SAFE_TO_RETRY.includes(err.code) && attempts < 5) //  
+                return this.#_query(query, values, ++attempts);
+            return Promise.reject(err);
+        }
+    }
+
+    async query (query, values) {
+
+        if (!this.ready)
+            return Promise.reject(new Error('MariaDB not ready'));
+
+        let batch = false;
+        if (values && typeof values.some === 'function')
+            batch = values.some(val => val instanceof Array);
+        this.logger.debug(`Incoming query (batch: ${batch})\n${query}\n${inspect(values)}`);
+
+        return this.#_query(query, values);
 
     }