[tracker/wip/carlosg/in-memory-databases: 1/5] libtracker-data: Support in-memory DBs in TrackerDBInterface

[Carlos Garnacho <carlosg src gnome org>]

commit 1262263939c1379dc3b367f570ff4b913a3cf714
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sat Feb 22 16:19:21 2020 +0100

    libtracker-data: Support in-memory DBs in TrackerDBInterface
    
    Add an IN_MEMORY flag, and an argument for a unique shared cache key
    (string-based). This key will be shared across all connections created
    by a TrackerDBManager, and will let all TrackerDBInterfaces created by
    it look into the same shared memory.
    
    The same happens when attaching graph databases, those separate dbs
    will be created in the shared cache, so they will be visible from all
    connections.

 src/libtracker-data/tracker-db-interface-sqlite.c | 61 +++++++++++++++++++----
 src/libtracker-data/tracker-db-interface-sqlite.h |  4 +-
 src/libtracker-data/tracker-db-manager.c          |  1 +
 3 files changed, 56 insertions(+), 10 deletions(-)
---
diff --git a/src/libtracker-data/tracker-db-interface-sqlite.c 
b/src/libtracker-data/tracker-db-interface-sqlite.c
index 61c3a1c11..074bf40f1 100644
--- a/src/libtracker-data/tracker-db-interface-sqlite.c
+++ b/src/libtracker-data/tracker-db-interface-sqlite.c
@@ -77,6 +77,7 @@ struct TrackerDBInterface {
        GObject parent_instance;
 
        gchar *filename;
+       gchar *shared_cache_key;
        sqlite3 *db;
 
        GHashTable *dynamic_statements;
@@ -157,7 +158,8 @@ static gboolean            db_cursor_iter_next                      (TrackerDBCu
 enum {
        PROP_0,
        PROP_FILENAME,
-       PROP_FLAGS
+       PROP_FLAGS,
+       PROP_SHARED_CACHE_KEY,
 };
 
 enum {
@@ -1914,8 +1916,9 @@ open_database (TrackerDBInterface  *db_interface,
 {
        int mode;
        int result;
+       gchar *uri;
 
-       g_assert (db_interface->filename != NULL);
+       g_assert (db_interface->filename != NULL || db_interface->shared_cache_key != NULL);
 
        if ((db_interface->flags & TRACKER_DB_INTERFACE_READONLY) == 0) {
                mode = SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE;
@@ -1923,7 +1926,16 @@ open_database (TrackerDBInterface  *db_interface,
                mode = SQLITE_OPEN_READONLY;
        }
 
-       result = sqlite3_open_v2 (db_interface->filename, &db_interface->db, mode | SQLITE_OPEN_NOMUTEX, 
NULL);
+       if ((db_interface->flags & TRACKER_DB_INTERFACE_IN_MEMORY) != 0) {
+               mode |= SQLITE_OPEN_MEMORY | SQLITE_OPEN_SHAREDCACHE | SQLITE_OPEN_URI;
+               uri = g_strdup_printf ("file:%s", db_interface->shared_cache_key);
+       } else {
+               uri = g_strdup (db_interface->filename);
+       }
+
+       result = sqlite3_open_v2 (uri, &db_interface->db, mode | SQLITE_OPEN_NOMUTEX, NULL);
+       g_free (uri);
+
        if (result != SQLITE_OK) {
                const gchar *str;
 
@@ -1931,10 +1943,13 @@ open_database (TrackerDBInterface  *db_interface,
                g_set_error (error,
                             TRACKER_DB_INTERFACE_ERROR,
                             TRACKER_DB_OPEN_ERROR,
-                            "Could not open sqlite3 database:'%s': %s", db_interface->filename, str);
+                            "Could not open sqlite3 database:'%s': %s",
+                            db_interface->filename ? db_interface->filename : "memory",
+                            str);
                return;
        } else {
-               g_debug ("Opened sqlite3 database:'%s'", db_interface->filename);
+               g_debug ("Opened sqlite3 database:'%s'",
+                        db_interface->filename? db_interface->filename : "memory");
        }
 
        /* Set our unicode collation function */
@@ -1999,6 +2014,9 @@ tracker_db_interface_sqlite_set_property (GObject       *object,
        case PROP_FILENAME:
                db_iface->filename = g_value_dup_string (value);
                break;
+       case PROP_SHARED_CACHE_KEY:
+               db_iface->shared_cache_key = g_value_dup_string (value);
+               break;
        default:
                G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
        }
@@ -2021,6 +2039,9 @@ tracker_db_interface_sqlite_get_property (GObject    *object,
        case PROP_FILENAME:
                g_value_set_string (value, db_iface->filename);
                break;
+       case PROP_SHARED_CACHE_KEY:
+               g_value_set_string (value, db_iface->shared_cache_key);
+               break;
        default:
                G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
        }
@@ -2419,6 +2440,7 @@ tracker_db_interface_sqlite_finalize (GObject *object)
        g_debug ("Closed sqlite3 database:'%s'", db_interface->filename);
 
        g_free (db_interface->filename);
+       g_free (db_interface->shared_cache_key);
 
        if (db_interface->user_data && db_interface->user_data_destroy_notify)
                db_interface->user_data_destroy_notify (db_interface->user_data);
@@ -2450,6 +2472,14 @@ tracker_db_interface_class_init (TrackerDBInterfaceClass *class)
                                                             "Interface flags",
                                                             TRACKER_TYPE_DB_INTERFACE_FLAGS, 0,
                                                             G_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY));
+
+       g_object_class_install_property (object_class,
+                                        PROP_SHARED_CACHE_KEY,
+                                        g_param_spec_string ("shared-cache-key",
+                                                             "Shared cache key",
+                                                             "Shared cache key",
+                                                             NULL,
+                                                             G_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY));
 }
 
 static void
@@ -2822,6 +2852,7 @@ tracker_db_interface_execute_vquery (TrackerDBInterface  *db_interface,
 
 TrackerDBInterface *
 tracker_db_interface_sqlite_new (const gchar              *filename,
+                                 const gchar              *shared_cache_key,
                                  TrackerDBInterfaceFlags   flags,
                                  GError                  **error)
 {
@@ -2833,6 +2864,7 @@ tracker_db_interface_sqlite_new (const gchar              *filename,
                                 &internal_error,
                                 "filename", filename,
                                 "flags", flags,
+                                "shared-cache-key", shared_cache_key,
                                 NULL);
 
        if (internal_error) {
@@ -3545,13 +3577,24 @@ tracker_db_interface_attach_database (TrackerDBInterface  *db_interface,
                                       const gchar         *name,
                                       GError             **error)
 {
-       gchar *sql, *path;
+       gchar *sql, *uri = NULL;
        sqlite3_stmt *stmt;
        gboolean retval;
 
-       path = g_file_get_path (file);
-       sql = g_strdup_printf ("ATTACH DATABASE \"%s\" AS \"%s\"", path, name);
-       g_free (path);
+       g_return_val_if_fail (file || db_interface->shared_cache_key, FALSE);
+
+       if (file) {
+               uri = g_file_get_path (file);
+       } else if (db_interface->shared_cache_key &&
+                  (db_interface->flags & TRACKER_DB_INTERFACE_IN_MEMORY) != 0) {
+               uri = g_strdup_printf ("file:%s-%s?mode=memory&cache=shared",
+                                       db_interface->shared_cache_key,
+                                       name);
+       }
+
+       sql = g_strdup_printf ("ATTACH DATABASE \"%s\" AS \"%s\"",
+                              uri, name);
+       g_free (uri);
 
        stmt = tracker_db_interface_prepare_stmt (db_interface, sql, error);
        g_free (sql);
diff --git a/src/libtracker-data/tracker-db-interface-sqlite.h 
b/src/libtracker-data/tracker-db-interface-sqlite.h
index f8dc3c07b..9655f1999 100644
--- a/src/libtracker-data/tracker-db-interface-sqlite.h
+++ b/src/libtracker-data/tracker-db-interface-sqlite.h
@@ -39,10 +39,12 @@ typedef void (*TrackerDBWalCallback) (TrackerDBInterface *iface,
 
 typedef enum {
        TRACKER_DB_INTERFACE_READONLY  = 1 << 0,
-       TRACKER_DB_INTERFACE_USE_MUTEX = 1 << 1
+       TRACKER_DB_INTERFACE_USE_MUTEX = 1 << 1,
+       TRACKER_DB_INTERFACE_IN_MEMORY = 1 << 2,
 } TrackerDBInterfaceFlags;
 
 TrackerDBInterface *tracker_db_interface_sqlite_new                    (const gchar              *filename,
+                                                                        const gchar              
*shared_cache_key,
                                                                         TrackerDBInterfaceFlags   flags,
                                                                         GError                  **error);
 gint64              tracker_db_interface_sqlite_get_last_insert_id     (TrackerDBInterface       *interface);
diff --git a/src/libtracker-data/tracker-db-manager.c b/src/libtracker-data/tracker-db-manager.c
index 56410448f..226be7cc8 100644
--- a/src/libtracker-data/tracker-db-manager.c
+++ b/src/libtracker-data/tracker-db-manager.c
@@ -905,6 +905,7 @@ tracker_db_manager_create_db_interface (TrackerDBManager  *db_manager,
                flags |= TRACKER_DB_INTERFACE_USE_MUTEX;
 
        connection = tracker_db_interface_sqlite_new (db_manager->db.abs_filename,
+                                                     NULL,
                                                      flags,
                                                      &internal_error);
        if (internal_error) {