Better handle large numbers of messages in cache on startup

app/sql.js

@@ -42,6 +42,7 @@ module.exports = {
   getNextExpiringMessage,
   getMessagesByConversation,
 
+  getUnprocessedCount,
   getAllUnprocessed,
   saveUnprocessed,
   getUnprocessedById,
@@ -962,6 +963,16 @@ async function getUnprocessedById(id) {
   return jsonToObject(row.json);
 }
 
+async function getUnprocessedCount() {
+  const row = await db.get('SELECT count(*) from unprocessed;');
+
+  if (!row) {
+    throw new Error('getMessageCount: Unable to get count of unprocessed');
+  }
+
+  return row['count(*)'];
+}
+
 async function getAllUnprocessed() {
   const rows = await db.all(
     'SELECT json FROM unprocessed ORDER BY timestamp ASC;'