Does bitcoind using dynamic fees by default ? I mean, that at the moment if it is necessary to use lower fee, bitcoind will set lower fee, if network is busy, then it will use higher fee..
By default, bitcoind will use estimate fee and uses the estimate to include a fee that would likely get the transaction to be confirmed within 2 blocks. If the network load is high, bitcoind would opt for a higher fee, if it is low, bitcoind would opt for a lower fee. At times, bitcoind would not be able to estimate the fee due to insufficient mempool data. In these situations, bitcoind uses a fee of 0.0002BTC/KB. Use -paytxfee=<fees in BTC/kb> to set the fee and override this option.