diff --git a/synapse/storage/databases/main/event_federation.py b/synapse/storage/databases/main/event_federation.py
index 945be1b2f62c..eac7d8590595 100644
--- a/synapse/storage/databases/main/event_federation.py
+++ b/synapse/storage/databases/main/event_federation.py
@@ -291,6 +291,7 @@ def _get_auth_chain_ids_using_cover_index_txn(
                 txn.execute(sql % (clause,), args)
 
                 for event_id, chain_id, sequence_number in txn:
+                    logger.debug(f"JASON: s1d, {event_id}: {chain_id}, {sequence_number}")
                     section_1_rows.add((event_id, chain_id, sequence_number))
 
         with Measure(
@@ -331,6 +332,59 @@ def _get_auth_chain_ids_using_cover_index_txn(
 
         section_2_rows = set()
 
+        with Measure(
+            self.hs.get_clock(),
+            "_get_auth_chain_ids_using_cover_index_txn.section_2_cache_retrieval",
+        ):
+            # Take a copy of the event_chains dict, as it will be mutated to remove
+            # entries that don't have to be pulled from the database later.
+            logger.debug(f"JASON: s2c, event_chains before: {event_chains}")
+            for chain_id, seq_no in dict(event_chains).items():
+                logger.debug(f"JASON: looking for cache entry: {chain_id}, {seq_no}")
+                s2_cache_entry = self._authchain_links_list.get(chain_id)
+                # the seq_no above references a specific set of chains to start
+                # processing at. The cache will contain(if an entry is there at all) all
+                # chains below that value. If newer information has been added since the
+                # last time the cache was loaded, then the seq_no will have no matching
+                # origin_sequence_number below(a literal 'equals'). Watch for that, as
+                # if it doesn't exist, then it's time to reload.
+                s2_checkpoint = True
+                if s2_cache_entry is not None:
+                    logger.debug(f"JASON: s2c, cache entry found: {chain_id}, {s2_cache_entry}")
+                    for origin_seq_number, target_set_info in s2_cache_entry.items():
+                        # If we pass the checkpoint, this will be removed from the cache
+
+                        # NOTE Always plan on a reload unless we hit a match where:
+                        # seq_no - 1 == origin seq number, indicating we found the max
+                        # but only if seq_no is greater than 1
+                        logger.debug(f"JASON FOCUS: seq_no {seq_no} origin_seq_number {origin_seq_number}")
+                        if (seq_no > 1 and (seq_no - 1) == origin_seq_number) or (seq_no == 1 and seq_no == origin_seq_number):
+                            logger.debug("JASON: not reloading cache entry")
+                            s2_checkpoint = False
+                        # This condition gates that a sequence number GREATER than what
+                        # is needed is not used.
+                        if origin_seq_number <= seq_no:
+                            # chains are only reachable if the origin sequence number of
+                            # the link is less than the max sequence number in the
+                            # origin chain.
+                            for target_chain_id, target_seq_no in target_set_info:
+                                # We use a (0, 0) tuple as a placeholder in the cache
+                                # to represent that this particular target set doesn't
+                                # exist in the database and therefore will never be
+                                # in the cache. Typically, this is an origin event and
+                                # will have nothing prior to it, hence no chain.
+                                if (target_chain_id, target_seq_no) != (0, 0):
+                                    # This is slightly more optimized than using max()
+                                    target_seq_max_result = chains.get(
+                                        target_chain_id, 0
+                                    )
+                                    if target_seq_no > target_seq_max_result:
+                                        chains[target_chain_id] = target_seq_no
+
+                    if not s2_checkpoint:
+                        del event_chains[chain_id]
+
+        logger.debug(f"JASON: s2c, event chains after: {event_chains}")
         with Measure(
             self.hs.get_clock(),
             "_get_auth_chain_ids_using_cover_index_txn.section_2_database",
@@ -390,6 +444,31 @@ def _get_auth_chain_ids_using_cover_index_txn(
                 if max_sequence_result > 0:
                     chains[chain_id] = max_sequence_result
 
+        with Measure(
+            self.hs.get_clock(),
+            "_get_auth_chain_ids_using_cover_index_txn.section_2_postprocessing_cache",
+        ):
+            # For this block, first build the cache entries in an efficient way, then
+            # set them into the cache itself.
+            cache_entries: Dict[int, Dict[int, Set[Tuple[int, int]]]] = {}
+            seen_during_batching = set()
+            for (
+                origin_chain_id,
+                origin_sequence_number,
+                target_chain_id,
+                target_sequence_number,
+            ) in section_2_rows:
+                logger.debug(f"JASON: s2dpc, processing row {origin_chain_id}, {origin_sequence_number}: {target_chain_id}, {target_sequence_number}")
+                seen_during_batching.add(origin_chain_id)
+                cache_entries.setdefault(origin_chain_id, {}).setdefault(
+                    origin_sequence_number, set()
+                ).add((target_chain_id, target_sequence_number))
+
+            for origin_chain_id, cache_entry in cache_entries.items():
+                logger.debug(f"JASON: s2dpc, adding to cache {origin_chain_id}: {cache_entry}")
+                self._authchain_links_list.set(origin_chain_id, cache_entry)
+            logger.debug(f"JASON: seen during batching {seen_during_batching}")
+
         # Now for each chain we figure out the maximum sequence number reachable
         # from *any* event ID. Events with a sequence less than that are in the
         # auth chain.
@@ -453,6 +532,7 @@ def _get_auth_chain_ids_using_cover_index_txn(
             "_get_auth_chain_ids_using_cover_index_txn.section_3_postprocessing_cache",
         ):
             for event_id, chain_id, sequence_number in section_3_rows:
+                logger.debug(f"JASON: s3d, {event_id}: {chain_id}, {sequence_number}")
                 s3_cache_entry = self._authchain_chain_info_to_event_id.get(
                     chain_id, update_last_access=False
                 )