perf(history): enable sql index on chat_id in history table

This makes every query with a "WHERE history.chat_id" clause quicker,
improving history load time by 50% on my profile.

Related to #5812

src/persistence/history.cpp

@@ -26,7 +26,7 @@
 #include "db/rawdatabase.h"
 
 namespace {
-static constexpr int SCHEMA_VERSION = 3;
+static constexpr int SCHEMA_VERSION = 4;
 
 bool createCurrentSchema(RawDatabase& db)
 {
@@ -63,6 +63,9 @@ bool createCurrentSchema(RawDatabase& db)
         "file_state INTEGER NOT NULL);"
         "CREATE TABLE faux_offline_pending (id INTEGER PRIMARY KEY);"
         "CREATE TABLE broken_messages (id INTEGER PRIMARY KEY);"));
+    // sqlite doesn't support including the index as part of the CREATE TABLE statement, so add a second query
+    queries += RawDatabase::Query(
+        "CREATE INDEX chat_id_idx on history (chat_id);");
     queries += RawDatabase::Query(QStringLiteral("PRAGMA user_version = %1;").arg(SCHEMA_VERSION));
     return db.execNow(queries);
 }
@@ -178,6 +181,18 @@ bool dbSchema2to3(RawDatabase& db)
     return db.execNow(upgradeQueries);
 }
 
+bool dbSchema3to4(RawDatabase& db)
+{
+    QVector<RawDatabase::Query> upgradeQueries;
+    upgradeQueries += RawDatabase::Query{QString(
+        "CREATE INDEX chat_id_idx on history (chat_id);")};
+
+    upgradeQueries += RawDatabase::Query(QStringLiteral("PRAGMA user_version = 4;"));
+
+    return db.execNow(upgradeQueries);
+}
+
+
 /**
 * @brief Upgrade the db schema
 * @note On future alterations of the database all you have to do is bump the SCHEMA_VERSION
@@ -252,6 +267,13 @@ void dbSchemaUpgrade(std::shared_ptr<RawDatabase>& db)
             return;
        }
        qDebug() << "Database upgraded incrementally to schema version 3";
+    case 3:
+       if (!dbSchema3to4(*db)) {
+            qCritical() << "Failed to upgrade db to schema version 4, aborting";
+            db.reset();
+            return;
+       }
+       qDebug() << "Database upgraded incrementally to schema version 4";
     // etc.
     default:
         qInfo() << "Database upgrade finished (databaseSchemaVersion" << databaseSchemaVersion

test/persistence/dbschema_test.cpp

@@ -37,6 +37,7 @@ private slots:
     void test0to1();
     void test1to2();
     void test2to3();
+    void test3to4();
     void cleanupTestCase();
 private:
     bool initSucess{false};
@@ -50,9 +51,12 @@ const QString testFileList[] = {
     "testIsNewDbFalse.db",
     "test0to1.db",
     "test1to2.db",
-    "test2to3.db"
+    "test2to3.db",
+    "test3to4.db"
 };
 
+// db schemas can be select with "SELECT name, sql FROM sqlite_master;" on the database.
+
 const QMap<QString, QString> schema0 {
     {"aliases", "CREATE TABLE aliases (id INTEGER PRIMARY KEY, owner INTEGER, display_name BLOB NOT NULL, UNIQUE(owner, display_name))"},
     {"faux_offline_pending", "CREATE TABLE faux_offline_pending (id INTEGER PRIMARY KEY)"},
@@ -82,6 +86,17 @@ const QMap<QString, QString> schema2 {
 // move stuck 0-length action messages to the existing "broken_messages" table. Not a real schema upgrade.
 const auto schema3 = schema2;
 
+// create index in history table on chat_id to improve query speed. Not a real schema upgrade.
+const QMap<QString, QString> schema4 {
+    {"aliases", "CREATE TABLE aliases (id INTEGER PRIMARY KEY, owner INTEGER, display_name BLOB NOT NULL, UNIQUE(owner, display_name))"},
+    {"faux_offline_pending", "CREATE TABLE faux_offline_pending (id INTEGER PRIMARY KEY)"},
+    {"file_transfers", "CREATE TABLE file_transfers (id INTEGER PRIMARY KEY, chat_id INTEGER NOT NULL, file_restart_id BLOB NOT NULL, file_name BLOB NOT NULL, file_path BLOB NOT NULL, file_hash BLOB NOT NULL, file_size INTEGER NOT NULL, direction INTEGER NOT NULL, file_state INTEGER NOT NULL)"},
+    {"history", "CREATE TABLE history (id INTEGER PRIMARY KEY, timestamp INTEGER NOT NULL, chat_id INTEGER NOT NULL, sender_alias INTEGER NOT NULL, message BLOB NOT NULL, file_id INTEGER)"},
+    {"peers", "CREATE TABLE peers (id INTEGER PRIMARY KEY, public_key TEXT NOT NULL UNIQUE)"},
+    {"broken_messages", "CREATE TABLE broken_messages (id INTEGER PRIMARY KEY)"},
+    {"chat_id_idx", "CREATE INDEX chat_id_idx on history (chat_id)"}
+};
+
 void TestDbSchema::initTestCase()
 {
     for (const auto& path : testFileList) {
@@ -132,7 +147,7 @@ void TestDbSchema::testCreation()
     QVector<RawDatabase::Query> queries;
     auto db = std::shared_ptr<RawDatabase>{new RawDatabase{"testCreation.db", {}, {}}};
     QVERIFY(createCurrentSchema(*db));
-    verifyDb(db, schema3);
+    verifyDb(db, schema4);
 }
 
 void TestDbSchema::testIsNewDb()
@@ -314,5 +329,13 @@ void TestDbSchema::test2to3()
     verifyDb(db, schema3);
 }
 
+void TestDbSchema::test3to4()
+{
+    auto db = std::shared_ptr<RawDatabase>{new RawDatabase{"test3to4.db", {}, {}}};
+    createSchemaAtVersion(db, schema3);
+    QVERIFY(dbSchema3to4(*db));
+    verifyDb(db, schema4);
+}
+
 QTEST_GUILESS_MAIN(TestDbSchema)
 #include "dbschema_test.moc"