From: Austin Clements <amdragon@MIT.EDU>
To: notmuch@notmuchmail.org
Subject: [PATCH 08/14] lib: Simplify upgrade code using a transaction
Date: Sat, 26 Jul 2014 23:52:47 -0400
Message-Id: <1406433173-19169-9-git-send-email-amdragon@mit.edu>
In-Reply-To: <1406433173-19169-1-git-send-email-amdragon@mit.edu>
References: <1406433173-19169-1-git-send-email-amdragon@mit.edu>
Precedence: list

Previously, the upgrade was organized as two passes -- an upgrade
pass, and a separate cleanup pass -- so the database was always in a
valid state.  This change substantially simplifies this code by
performing the upgrade in a transaction and combining both passes in
to one.  This 1) eliminates a lot of duplicate code between the
passes, 2) speeds up the upgrade process, 3) makes progress reporting
more accurate, 4) eliminates the potential for stale data if the
upgrade is interrupted during the cleanup pass, and 5) makes it easier
to reason about the safety of the upgrade code.
---
 lib/database.cc | 67 ++++++---------------------------------------------------
 1 file changed, 7 insertions(+), 60 deletions(-)

diff --git a/lib/database.cc b/lib/database.cc
index 03eef3e..0be7180 100644
--- a/lib/database.cc
+++ b/lib/database.cc
@@ -1238,6 +1238,9 @@ notmuch_database_upgrade (notmuch_database_t *notmuch,
 	timer_is_active = TRUE;
     }
 
+    /* Perform the upgrade in a transaction. */
+    db->begin_transaction (true);
+
     /* Before version 1, each message document had its filename in the
      * data field. Copy that into the new format by calling
      * notmuch_message_add_filename.
@@ -1265,6 +1268,7 @@ notmuch_database_upgrade (notmuch_database_t *notmuch,
 	    filename = _notmuch_message_talloc_copy_data (message);
 	    if (filename && *filename != '\0') {
 		_notmuch_message_add_filename (message, filename);
+		_notmuch_message_clear_data (message);
 		_notmuch_message_sync (message);
 	    }
 	    talloc_free (filename);
@@ -1312,6 +1316,8 @@ notmuch_database_upgrade (notmuch_database_t *notmuch,
 						       NOTMUCH_FIND_CREATE, &status);
 		notmuch_directory_set_mtime (directory, mtime);
 		notmuch_directory_destroy (directory);
+
+		db->delete_document (*p);
 	    }
 	}
     }
@@ -1353,67 +1359,8 @@ notmuch_database_upgrade (notmuch_database_t *notmuch,
     notmuch->features |= NOTMUCH_FEATURES_CURRENT;
     db->set_metadata ("features", _print_features (local, notmuch->features));
     db->set_metadata ("version", STRINGIFY (NOTMUCH_DATABASE_VERSION));
-    db->flush ();
-
-    /* Now that the upgrade is complete we can remove the old data
-     * and documents that are no longer needed. */
-    if (version < 1) {
-	notmuch_query_t *query = notmuch_query_create (notmuch, "");
-	notmuch_messages_t *messages;
-	notmuch_message_t *message;
-	char *filename;
-
-	for (messages = notmuch_query_search_messages (query);
-	     notmuch_messages_valid (messages);
-	     notmuch_messages_move_to_next (messages))
-	{
-	    if (do_progress_notify) {
-		progress_notify (closure, (double) count / total);
-		do_progress_notify = 0;
-	    }
-
-	    message = notmuch_messages_get (messages);
-
-	    filename = _notmuch_message_talloc_copy_data (message);
-	    if (filename && *filename != '\0') {
-		_notmuch_message_clear_data (message);
-		_notmuch_message_sync (message);
-	    }
-	    talloc_free (filename);
-
-	    notmuch_message_destroy (message);
-	}
 
-	notmuch_query_destroy (query);
-    }
-
-    if (version < 1) {
-	Xapian::TermIterator t, t_end;
-
-	t_end = notmuch->xapian_db->allterms_end ("XTIMESTAMP");
-
-	for (t = notmuch->xapian_db->allterms_begin ("XTIMESTAMP");
-	     t != t_end;
-	     t++)
-	{
-	    Xapian::PostingIterator p, p_end;
-	    std::string term = *t;
-
-	    p_end = notmuch->xapian_db->postlist_end (term);
-
-	    for (p = notmuch->xapian_db->postlist_begin (term);
-		 p != p_end;
-		 p++)
-	    {
-		if (do_progress_notify) {
-		    progress_notify (closure, (double) count / total);
-		    do_progress_notify = 0;
-		}
-
-		db->delete_document (*p);
-	    }
-	}
-    }
+    db->commit_transaction ();
 
     if (timer_is_active) {
 	/* Now stop the timer. */
-- 
2.0.0