From 856d5130404b29d8f391e05b15a82776dbdf93e3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Markus=20M=C3=A4kel=C3=A4?= <markus.makela@mariadb.com>
Date: Fri, 15 Jun 2018 01:12:24 +0300
Subject: [PATCH] MXS-1924: Enable WAL mode for sqlite

The mysqlauth SQLite database is now opened in WAL mode if possible. This
should prevent lockups of the database when the list of users is updated.

Also moved the starting of the SQLite transaction one level up to also
include the delete part in it. This should further reduce the effects of
updating users.
---
 .../modules/authenticator/MySQLAuth/dbusers.c |  7 ++--
 .../authenticator/MySQLAuth/mysql_auth.c      | 40 +++++++++++++------
 .../authenticator/MySQLAuth/mysql_auth.h      |  3 +-
 3 files changed, 33 insertions(+), 17 deletions(-)

diff --git a/server/modules/authenticator/MySQLAuth/dbusers.c b/server/modules/authenticator/MySQLAuth/dbusers.c
index af8bc6f68..72c43c10d 100644
--- a/server/modules/authenticator/MySQLAuth/dbusers.c
+++ b/server/modules/authenticator/MySQLAuth/dbusers.c
@@ -776,8 +776,6 @@ int get_users_from_server(MYSQL *con, SERVER_REF *server, SERVICE *service, SERV
 
             if (result)
             {
-                start_sqlite_transaction(instance->handle);
-
                 MYSQL_ROW row;
 
                 while ((row = mysql_fetch_row(result)))
@@ -804,8 +802,6 @@ int get_users_from_server(MYSQL *con, SERVER_REF *server, SERVICE *service, SERV
                     }
                 }
 
-                commit_sqlite_transaction(instance->handle);
-
                 mysql_free_result(result);
             }
         }
@@ -874,6 +870,7 @@ static int get_users(SERV_LISTENER *listener, bool skip_local)
 
     /** Delete the old users */
     MYSQL_AUTH *instance = (MYSQL_AUTH*)listener->auth_instance;
+    start_sqlite_transaction(instance->handle);
     delete_mysql_users(instance->handle);
 
     SERVER_REF *server = service->dbref;
@@ -921,6 +918,8 @@ static int get_users(SERV_LISTENER *listener, bool skip_local)
         }
     }
 
+    commit_sqlite_transaction(instance->handle);
+
     MXS_FREE(dpwd);
 
     if (no_active_servers)
diff --git a/server/modules/authenticator/MySQLAuth/mysql_auth.c b/server/modules/authenticator/MySQLAuth/mysql_auth.c
index 672abd1d1..53b23363a 100644
--- a/server/modules/authenticator/MySQLAuth/mysql_auth.c
+++ b/server/modules/authenticator/MySQLAuth/mysql_auth.c
@@ -129,25 +129,41 @@ static void get_database_path(SERV_LISTENER *port, char *dest, size_t size)
 
 static bool open_instance_database(const char *path, sqlite3 **handle)
 {
+    bool rval = true;
+
     if (sqlite3_open_v2(path, handle, db_flags, NULL) != SQLITE_OK)
     {
         MXS_ERROR("Failed to open SQLite3 handle.");
-        return false;
+        rval = false;
     }
-
-    char *err;
-
-    if (sqlite3_exec(*handle, users_create_sql, NULL, NULL, &err) != SQLITE_OK ||
-        sqlite3_exec(*handle, databases_create_sql, NULL, NULL, &err) != SQLITE_OK ||
-        sqlite3_exec(*handle, pragma_sql, NULL, NULL, &err) != SQLITE_OK)
+    else
     {
-        MXS_ERROR("Failed to create database: %s", err);
-        sqlite3_free(err);
-        sqlite3_close_v2(*handle);
-        return false;
+        char *err;
+
+        if (sqlite3_exec(*handle, users_create_sql, NULL, NULL, &err) != SQLITE_OK ||
+            sqlite3_exec(*handle, databases_create_sql, NULL, NULL, &err) != SQLITE_OK)
+        {
+            MXS_ERROR("Failed to create database: %s", err);
+            sqlite3_free(err);
+            sqlite3_close_v2(*handle);
+            rval = false;
+        }
+        else if (sqlite3_exec(*handle, pragma_sql, NULL, NULL, &err) != SQLITE_OK)
+        {
+            sqlite3_free(err);
+            MXS_NOTICE("Could not open SQLite database in WAL mode, using in-memory mode");
+
+            if (sqlite3_exec(*handle, old_pragma_sql, NULL, NULL, &err) != SQLITE_OK)
+            {
+                MXS_ERROR("Failed to set in-memory mode: %s", err);
+                sqlite3_free(err);
+                sqlite3_close_v2(*handle);
+                rval = false;
+            }
+        }
     }
 
-    return true;
+    return rval;
 }
 
 static bool open_client_database(const char *path, sqlite3 **handle)
diff --git a/server/modules/authenticator/MySQLAuth/mysql_auth.h b/server/modules/authenticator/MySQLAuth/mysql_auth.h
index ae289e202..2de5926f5 100644
--- a/server/modules/authenticator/MySQLAuth/mysql_auth.h
+++ b/server/modules/authenticator/MySQLAuth/mysql_auth.h
@@ -58,7 +58,8 @@ static const char databases_create_sql[] =
     "CREATE TABLE IF NOT EXISTS " MYSQLAUTH_DATABASES_TABLE_NAME "(db varchar(255))";
 
 /** PRAGMA configuration options for SQLite */
-static const char pragma_sql[] = "PRAGMA JOURNAL_MODE=MEMORY";
+static const char pragma_sql[]     = "PRAGMA journal_mode=WAL";
+static const char old_pragma_sql[] = "PRAGMA journal_mode=MEMORY";
 
 /** Query that checks if there's a grant for the user being authenticated */
 static const char mysqlauth_validate_user_query[] =