fee_policy: lower min relay fee from 1 sat/byte to 0.1 s/b

- minrelayfee is still server-reported, but the clamps are changed from [1, 50] to [0.1, 50] sat/vbyte
- dynamic feerates coming from the estimator are still clamped to [1, 1500] sat/vbyte

ref https://github.com/bitcoin/bitcoin/pull/33106

electrum/bitcoin.py

@@ -325,14 +325,14 @@ def construct_script(
 
 def relayfee(network: 'Network' = None) -> int:
     """Returns feerate in sat/kbyte."""
-    from .fee_policy import FEERATE_DEFAULT_RELAY, FEERATE_MAX_RELAY
+    from .fee_policy import FEERATE_MIN_RELAY, FEERATE_DEFAULT_RELAY, FEERATE_MAX_RELAY
     if network and network.relay_fee is not None:
         fee = network.relay_fee
     else:
         fee = FEERATE_DEFAULT_RELAY
     # sanity safeguards, as network.relay_fee is coming from a server:
     fee = min(fee, FEERATE_MAX_RELAY)
-    fee = max(fee, FEERATE_DEFAULT_RELAY)
+    fee = max(fee, FEERATE_MIN_RELAY)
     return fee
 
 

electrum/fee_policy.py

@@ -25,8 +25,10 @@ FEERATE_MAX_DYNAMIC = 1500000
 FEERATE_WARNING_HIGH_FEE = 600000
 FEERATE_FALLBACK_STATIC_FEE = 150000
 FEERATE_REGTEST_STATIC_FEE = FEERATE_FALLBACK_STATIC_FEE  # hardcoded fee used on regtest
-FEERATE_DEFAULT_RELAY = 1000
+FEERATE_MIN_RELAY = 100
+FEERATE_DEFAULT_RELAY = 1000  # conservative "min relay fee"
 FEERATE_MAX_RELAY = 50000
+assert FEERATE_MIN_RELAY <= FEERATE_DEFAULT_RELAY <= FEERATE_MAX_RELAY
 
 # warn user if fee/amount for on-chain tx is higher than this
 FEE_RATIO_HIGH_WARNING = 0.05
@@ -288,6 +290,8 @@ def impose_hard_limits_on_fee(func):
         if fee is None:
             return fee
         fee = min(FEERATE_MAX_DYNAMIC, fee)
+        # Clamp dynamic feerates with conservative min relay fee,
+        # to ensure txs propagate well:
         fee = max(FEERATE_DEFAULT_RELAY, fee)
         return fee
     return get_fee_within_limits
@@ -359,7 +363,7 @@ class FeeHistogram:
             slot = min(item[1], bytes_limit-bytes_current)
             bytes_current += slot
             capped_histogram.append([
-                max(FEERATE_DEFAULT_RELAY/1000, item[0]),  # clamped to [FEERATE_DEFAULT_RELAY/1000,inf[
+                max(FEERATE_MIN_RELAY/1000, item[0]),  # clamped to [FEERATE_MIN_RELAY/1000,inf[
                 slot,  # width of bucket
                 bytes_current,  # cumulative depth at far end of bucket
             ])