In the log I see things like:

    2017-09-13 03:54:33 init message: Rescanning...
    2017-09-13 03:54:33 Rescanning last 68616 blocks (from block 416339)...
    2017-09-13 03:54:40 AddToWallet xxxxx  update
    2017-09-13 03:55:33 Still rescanning. At block 418849. Progress=0.549138

I would be interested to see the wallet file name on each of these log lines.

Would there be any interest in merging such a PR?
{
    static std::atomic<bool> fOneThread(false);
    if (fOneThread.exchange(true)) {
        return;
    }
    if (!gArgs.GetBoolArg("-flushwallet", DEFAULT_FLUSHWALLET)) {
        return;
    }
    for (const std::shared_ptr<CWallet>& pwallet : GetWallets()) {
        WalletDatabase& dbh = pwallet->GetDBHandle();
        unsigned int nUpdateCounter = dbh.nUpdateCounter;
        if (dbh.nLastSeen != nUpdateCounter) {
            dbh.nLastSeen = nUpdateCounter;
            dbh.nLastWalletUpdate = GetTime();
        }
        if (dbh.nLastFlushed != nUpdateCounter && GetTime() - dbh.nLastWalletUpdate >= 2) {
            if (BerkeleyBatch::PeriodicFlush(dbh)) {
                dbh.nLastFlushed = nUpdateCounter;
            }
        }
    }
    fOneThread = false;
}
bool WalletBatch::Recover(const fs::path& wallet_path, void *callbackDataIn, bool (*recoverKVcallback)(void* callbackData, CDataStream ssKey, CDataStream ssValue), std::string& out_backup_filename)
{
    return BerkeleyBatch::Recover(wallet_path, callbackDataIn, recoverKVcallback, out_backup_filename);
}
bool WalletBatch::Recover(const fs::path& wallet_path, std::string& out_backup_filename)