[tracker] libtracker-data: Remove global interface

[Carlos Garnacho <carlosg src gnome org>]

commit e53e9da15b660249c798925a64fc2601eb18a458
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sat Nov 5 21:25:50 2016 +0100

    libtracker-data: Remove global interface
    
    We no longer need to restrict to a single TrackerDBInterface for the
    direct connection use. This also allows to maximize the throughput
    in clients performing multiple simultaneous async queries, as we're
    going from using a single TrackerDBInterface to satisfy all requests
    (with the locking overhead this involves) to using multiple database
    connections that can run different concurrent queries each.
    
    This (and the last commits) translates to faster concurrent access,
    which evolves close to linearly under much higher loads, instead of
    exponentially. It is expected though that O(n^m) happens again if
    the number of operations vastly exceed the number of interfaces
    serving requests, but that's much farther.
    
    As an example, the numbers when running multiple concurrent queries
    for "SELECT ?u WHERE { ?u a rdfs:Resource }" (returning 12897
    elements each in this computer) progress like this on an otherwise
    idle session:
    
    Simul. Queries      With            Without
    5               0,399s          0,437s
    10              0,700s          0,842s
    50              3,621s          4,285s
    100             7,315s          8,956s
    500            36,012s      1m 24,952s
    1000                1m 16,355s      8m 33,880s
    
    So as expected the numbers really shine when the thread contention
    is most noticeable, and quite close to linearly (eg. in the "with"
    column, every row is roughly 10x higher than the one corresponding
    to simultaneous queries/10)

 src/libtracker-data/tracker-db-manager.c |   17 -----------------
 1 files changed, 0 insertions(+), 17 deletions(-)
---
diff --git a/src/libtracker-data/tracker-db-manager.c b/src/libtracker-data/tracker-db-manager.c
index 30e89cf..93aed16 100644
--- a/src/libtracker-data/tracker-db-manager.c
+++ b/src/libtracker-data/tracker-db-manager.c
@@ -163,8 +163,6 @@ static guint                 u_cache_size;
 
 static GPrivate              interface_data_key = G_PRIVATE_INIT ((GDestroyNotify)g_object_unref);
 
-static TrackerDBInterface   *global_iface;
-
 /* mutex protecting DB manager initialization/shutdown */
 static GMutex                init_mutex;
 
@@ -1200,10 +1198,6 @@ db_manager_init_unlocked (TrackerDBManagerFlags   flags,
        resources_iface = tracker_db_manager_get_db_interfaces (&internal_error,
                                                                (flags & TRACKER_DB_MANAGER_READONLY) != 0,
                                                                1, TRACKER_DB_METADATA);
-       if (flags & TRACKER_DB_MANAGER_READONLY) {
-               /* libtracker-direct does not use per-thread interfaces */
-               global_iface = resources_iface;
-       }
 
        if (internal_error) {
                if ((!restoring_backup) && (flags & TRACKER_DB_MANAGER_READONLY) == 0) {
@@ -1298,12 +1292,6 @@ db_manager_shutdown_unlocked (void)
        g_free (user_data_dir);
        user_data_dir = NULL;
 
-       if (global_iface) {
-               /* libtracker-direct */
-               g_object_unref (global_iface);
-               global_iface = NULL;
-       }
-
        /* shutdown db interface in all threads */
        g_private_replace (&interface_data_key, NULL);
 
@@ -1470,11 +1458,6 @@ tracker_db_manager_get_db_interface (void)
 
        g_return_val_if_fail (initialized != FALSE, NULL);
 
-       if (global_iface) {
-               /* libtracker-direct */
-               return global_iface;
-       }
-
        interface = g_private_get (&interface_data_key);
 
        /* Ensure the interface is there */