[libcontacts] Append contacts in large batches

Batched append slows down the overall throughput, but is necessary
to give interactivity during startup with huge contact counts. With
10000 contacts, the penalty is less than 10% overall, and the app
remains usable during the append period.

src/seasidecache.cpp

@@ -2311,21 +2311,35 @@ void SeasideCache::applyPendingContactUpdates()
         const bool partialFetch = !detailTypes.isEmpty();
 
         QList<QContact> &appendedContacts((*it).second);
-        appendContacts(appendedContacts, type, partialFetch, detailTypes);
-
-        m_contactsToAppend.erase(it);
-
-        // This list has been processed - have we finished populating the group?
-        if (type == FilterFavorites && (m_populateProgress != FetchFavorites)) {
-            makePopulated(FilterFavorites);
-            qDebug() << "Favorites queried in" << m_timer.elapsed() << "ms";
-        } else if (type == FilterAll && (m_populateProgress != FetchMetadata)) {
-            makePopulated(FilterNone);
-            makePopulated(FilterAll);
-            qDebug() << "All queried in" << m_timer.elapsed() << "ms";
-        } else if (type == FilterOnline && (m_populateProgress != FetchOnline)) {
-            makePopulated(FilterOnline);
-            qDebug() << "Online queried in" << m_timer.elapsed() << "ms";
+
+        const int maxBatchSize = 200;
+        const int minBatchSize = 50;
+
+        if (appendedContacts.count() < maxBatchSize) {
+            // For a small number of contacts, append all at once
+            appendContacts(appendedContacts, type, partialFetch, detailTypes);
+            appendedContacts.clear();
+        } else {
+            // Append progressively in batches
+            appendContacts(appendedContacts.mid(0, minBatchSize), type, partialFetch, detailTypes);
+            appendedContacts = appendedContacts.mid(minBatchSize);
+        }
+
+        if (appendedContacts.isEmpty()) {
+            m_contactsToAppend.erase(it);
+
+            // This list has been processed - have we finished populating the group?
+            if (type == FilterFavorites && (m_populateProgress != FetchFavorites)) {
+                makePopulated(FilterFavorites);
+                qDebug() << "Favorites queried in" << m_timer.elapsed() << "ms";
+            } else if (type == FilterAll && (m_populateProgress != FetchMetadata)) {
+                makePopulated(FilterNone);
+                makePopulated(FilterAll);
+                qDebug() << "All queried in" << m_timer.elapsed() << "ms";
+            } else if (type == FilterOnline && (m_populateProgress != FetchOnline)) {
+                makePopulated(FilterOnline);
+                qDebug() << "Online queried in" << m_timer.elapsed() << "ms";
+            }
         }
     } else {
         QList<QPair<QSet<DetailTypeId>, QList<QContact> > >::iterator it = m_contactsToUpdate.begin();