[PATCH 08/14] lib: Simplify upgrade code using a transaction

[Mark Walters]

Hi

On Sun, 27 Jul 2014, Austin Clements <amdragon at MIT.EDU> wrote:
> 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.

I like this but I wonder if it has a side effect: I think with the
current code the user can interrupt the upgrade (ctrl-c) and continue
roughly where it left off. This looks like it means the whole upgrade
needs to be done in one go. Will this be a problem on large mail stores
(eg rlb with over 1M messages)?

I am not sure what could be done during the interrupted upgrade before
so maybe this is not a problem.

Best wishes

Mark


> ---
>  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
>
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