[WIP PATCH 1/4] lib: Only sync modified message documents

[Austin Clements]

From: Austin Clements <amdra...@mit.edu>

Previously, we updated the database copy of a message on every call to
_notmuch_message_sync, even if nothing had changed.  In particular,
this always happens on a thaw, so a freeze/thaw pair with no
modifications between still caused a database update.

We only modify message documents in a handful of places, so keep track
of whether the document has been modified and only sync it when
necessary.  This will be particularly important when we add message
revision tracking.
---
 lib/message.cc | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/lib/message.cc b/lib/message.cc
index a7a13cc..cf2fd7c 100644
--- a/lib/message.cc
+++ b/lib/message.cc
@@ -43,6 +43,9 @@ struct visible _notmuch_message {
      * if each flag has been initialized. */
     unsigned long lazy_flags;

+    /* Message document modified since last sync */
+    notmuch_bool_t modified;
+
     Xapian::Document doc;
     Xapian::termcount termpos;
 };
@@ -538,6 +541,7 @@ _notmuch_message_remove_terms (notmuch_message_t *message, 
const char *prefix)

        try {
            message->doc.remove_term ((*i));
+           message->modified = TRUE;
        } catch (const Xapian::InvalidArgumentError) {
            /* Ignore failure to remove non-existent term. */
        }
@@ -791,6 +795,7 @@ void
 _notmuch_message_clear_data (notmuch_message_t *message)
 {
     message->doc.set_data ("");
+    message->modified = TRUE;
 }

 static void
@@ -988,6 +993,7 @@ _notmuch_message_set_header_values (notmuch_message_t 
*message,
                            Xapian::sortable_serialise (time_value));
     message->doc.add_value (NOTMUCH_VALUE_FROM, from);
     message->doc.add_value (NOTMUCH_VALUE_SUBJECT, subject);
+    message->modified = TRUE;
 }

 /* Synchronize changes made to message->doc out into the database. */
@@ -999,8 +1005,12 @@ _notmuch_message_sync (notmuch_message_t *message)
     if (message->notmuch->mode == NOTMUCH_DATABASE_MODE_READ_ONLY)
        return;

+    if (! message->modified)
+       return;
+
     db = static_cast <Xapian::WritableDatabase *> 
(message->notmuch->xapian_db);
     db->replace_document (message->doc_id, message->doc);
+    message->modified = FALSE;
 }

 /* Delete a message document from the database. */
@@ -1075,6 +1085,7 @@ _notmuch_message_add_term (notmuch_message_t *message,
        return NOTMUCH_PRIVATE_STATUS_TERM_TOO_LONG;

     message->doc.add_term (term, 0);
+    message->modified = TRUE;

     talloc_free (term);

@@ -1143,6 +1154,7 @@ _notmuch_message_remove_term (notmuch_message_t *message,

     try {
        message->doc.remove_term (term);
+       message->modified = TRUE;
     } catch (const Xapian::InvalidArgumentError) {
        /* We'll let the philosopher's try to wrestle with the
         * question of whether failing to remove that which was not
-- 
2.1.0