Method tryGetConsistentMetadataSnapshot

src/Databases/DatabaseReplicated.cpp:632–679

}

std::map<String, String> DatabaseReplicated::tryGetConsistentMetadataSnapshot(const ZooKeeperPtr & zookeeper, UInt32 & max_log_ptr)
{
    std::map<String, String> table_name_to_metadata;
    constexpr int max_retries = 10;
    int iteration = 0;
    while (++iteration <= max_retries)
    {
        table_name_to_metadata.clear();
        LOG_DEBUG(log, "Trying to get consistent metadata snapshot for log pointer {}", max_log_ptr);
        Strings table_names = zookeeper->getChildren(zookeeper_path + "/metadata");

        std::vector<zkutil::ZooKeeper::FutureGet> futures;
        futures.reserve(table_names.size());
        for (const auto & table : table_names)
            futures.emplace_back(zookeeper->asyncTryGet(zookeeper_path + "/metadata/" + table));

        for (size_t i = 0; i < table_names.size(); ++i)
        {
            auto res = futures[i].get();
            if (res.error != Coordination::Error::ZOK)
                break;
            table_name_to_metadata.emplace(unescapeForFileName(table_names[i]), res.data);
        }

        UInt32 new_max_log_ptr = parse<UInt32>(zookeeper->get(zookeeper_path + "/max_log_ptr"));
        if (new_max_log_ptr == max_log_ptr && table_names.size() == table_name_to_metadata.size())
            break;

        if (max_log_ptr < new_max_log_ptr)
        {
            LOG_DEBUG(log, "Log pointer moved from {} to {}, will retry", max_log_ptr, new_max_log_ptr);
            max_log_ptr = new_max_log_ptr;
        }
        else
        {
            assert(max_log_ptr == new_max_log_ptr);
            assert(table_names.size() != table_name_to_metadata.size());
            LOG_DEBUG(log, "Cannot get metadata of some tables due to ZooKeeper error, will retry");
        }
    }

    if (max_retries < iteration)
        throw Exception(ErrorCodes::DATABASE_REPLICATION_FAILED, "Cannot get consistent metadata snapshot");

    LOG_DEBUG(log, "Got consistent metadata snapshot for log pointer {}", max_log_ptr);

    return table_name_to_metadata;
}

ASTPtr DatabaseReplicated::parseQueryFromMetadataInZooKeeper(const String & node_name, const String & query, ParserSettingsImpl dt)
{