Per default refetch the chain tip at most every 20 seconds

At the current state, every access to protocol params causes at least
one chain tip fetch. Due to the potential delay of this request, often
another protocol params fetch is triggered as well.

This significantly (and mostly unnecessarily) slows down transaction building.
This fix caches the chain tip for a default of 20 seconds (the average
slot time), making sure that subsequent calls to _is_chain_tip_updated
return without any delay, drastically speeding up tx building.

Author: nielstron

pycardano/backend/ogmios.py

@@ -2,6 +2,7 @@
 from datetime import datetime, timezone
 from enum import Enum
 from typing import Any, Dict, List, Optional, Tuple, Union
+import time
 
 import cbor2
 import requests
@@ -45,6 +46,7 @@ class OgmiosChainContext(ChainContext):
     _service_name: str
     _kupo_url: Optional[str]
     _last_known_block_slot: int
+    _last_chain_tip_fetch: float
     _genesis_param: Optional[GenesisParameters]
     _protocol_param: Optional[ProtocolParameters]
 
@@ -54,12 +56,15 @@ def __init__(
         network: Network,
         compact_result=True,
         kupo_url=None,
+        refetch_chain_tip_interval=20,
     ):
         self._ws_url = ws_url
         self._network = network
         self._service_name = "ogmios.v1:compact" if compact_result else "ogmios"
         self._kupo_url = kupo_url
         self._last_known_block_slot = 0
+        self._refetch_chain_tip_interval = refetch_chain_tip_interval
+        self._last_chain_tip_fetch = 0
         self._genesis_param = None
         self._protocol_param = None
 
@@ -110,8 +115,12 @@ def _query_utxos_by_tx_id(self, tx_id: str, index: int) -> List[List[JsonDict]]:
         return self._request(OgmiosQueryType.Query, args)
 
     def _is_chain_tip_updated(self):
+        # fetch at most every twenty seconds!
+        if time.time() - self._last_chain_tip_fetch < self._refetch_chain_tip_interval:
+            return False
+        self._last_chain_tip_fetch = time.time()
         slot = self.last_block_slot
-        if self._last_known_block_slot != slot:
+        if self._last_known_block_slot < slot:
             self._last_known_block_slot = slot
             return True
         else: