applyBacklog example

foreach ($this->mappings as $mapping) {
            if (!empty($indexNames) && !\in_array($mapping->getType(), $indexNames)) {
                continue;
            }

            $configuration = $this->indexFactory->createIndexConfiguration($shop, $mapping->getType());
            $shopIndex = new ShopIndex($configuration->getName(), $shop, $mapping->getType());

            $this->createIndex($configuration, $shopIndex);
            $this->updateMapping($shopIndex, $mapping);
            $this->populate($shopIndex, $helper);
            $this->applyBacklog($shopIndex, $lastBacklogId);
            $this->createAlias($configuration);
        }
    }

    /** * Removes unused indices */
    public function cleanupIndices()
    {
        $prefix = $this->indexFactory->getPrefix();
        $aliases = $this->client->indices()->getAliases();