Back out in-flight state caching changes. (#12126)

1 files changed, 25 insertions, 218 deletions

diff --git a/synapse/storage/databases/state/store.py b/synapse/storage/databases/state/store.py
index dadf3d1e3a..7614d76ac6 100644
--- a/synapse/storage/databases/state/store.py
+++ b/synapse/storage/databases/state/store.py
@@ -13,24 +13,11 @@
 # limitations under the License.
 
 import logging
-from typing import (
-    TYPE_CHECKING,
-    Collection,
-    Dict,
-    Iterable,
-    Optional,
-    Sequence,
-    Set,
-    Tuple,
-)
+from typing import TYPE_CHECKING, Collection, Dict, Iterable, List, Optional, Set, Tuple
 
 import attr
-from sortedcontainers import SortedDict
-
-from twisted.internet import defer
 
 from synapse.api.constants import EventTypes
-from synapse.logging.context import make_deferred_yieldable, run_in_background
 from synapse.storage._base import SQLBaseStore
 from synapse.storage.database import (
     DatabasePool,
@@ -42,12 +29,6 @@ from synapse.storage.state import StateFilter
 from synapse.storage.types import Cursor
 from synapse.storage.util.sequence import build_sequence_generator
 from synapse.types import MutableStateMap, StateKey, StateMap
-from synapse.util import unwrapFirstError
-from synapse.util.async_helpers import (
-    AbstractObservableDeferred,
-    ObservableDeferred,
-    yieldable_gather_results,
-)
 from synapse.util.caches.descriptors import cached
 from synapse.util.caches.dictionary_cache import DictionaryCache
 
@@ -56,8 +37,8 @@ if TYPE_CHECKING:
 
 logger = logging.getLogger(__name__)
 
+
 MAX_STATE_DELTA_HOPS = 100
-MAX_INFLIGHT_REQUESTS_PER_GROUP = 5
 
 
 @attr.s(slots=True, frozen=True, auto_attribs=True)
@@ -73,24 +54,6 @@ class _GetStateGroupDelta:
         return len(self.delta_ids) if self.delta_ids else 0
 
 
-def state_filter_rough_priority_comparator(
-    state_filter: StateFilter,
-) -> Tuple[int, int]:
-    """
-    Returns a comparable value that roughly indicates the relative size of this
-    state filter compared to others.
-    'Larger' state filters should sort first when using ascending order, so
-    this is essentially the opposite of 'size'.
-    It should be treated as a rough guide only and should not be interpreted to
-    have any particular meaning. The representation may also change
-
-    The current implementation returns a tuple of the form:
-        * -1 for include_others, 0 otherwise
-        * -(number of entries in state_filter.types)
-    """
-    return -int(state_filter.include_others), -len(state_filter.types)
-
-
 class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
     """A data store for fetching/storing state groups."""
 
@@ -143,12 +106,6 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
             500000,
         )
 
-        # Current ongoing get_state_for_groups in-flight requests
-        # {group ID -> {StateFilter -> ObservableDeferred}}
-        self._state_group_inflight_requests: Dict[
-            int, SortedDict[StateFilter, AbstractObservableDeferred[StateMap[str]]]
-        ] = {}
-
         def get_max_state_group_txn(txn: Cursor) -> int:
             txn.execute("SELECT COALESCE(max(id), 0) FROM state_groups")
             return txn.fetchone()[0]  # type: ignore
@@ -200,7 +157,7 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
         )
 
     async def _get_state_groups_from_groups(
-        self, groups: Sequence[int], state_filter: StateFilter
+        self, groups: List[int], state_filter: StateFilter
     ) -> Dict[int, StateMap[str]]:
         """Returns the state groups for a given set of groups from the
         database, filtering on types of state events.
@@ -271,170 +228,6 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
 
         return state_filter.filter_state(state_dict_ids), not missing_types
 
-    def _get_state_for_group_gather_inflight_requests(
-        self, group: int, state_filter_left_over: StateFilter
-    ) -> Tuple[Sequence[AbstractObservableDeferred[StateMap[str]]], StateFilter]:
-        """
-        Attempts to gather in-flight requests and re-use them to retrieve state
-        for the given state group, filtered with the given state filter.
-
-        If there are more than MAX_INFLIGHT_REQUESTS_PER_GROUP in-flight requests,
-        and there *still* isn't enough information to complete the request by solely
-        reusing others, a full state filter will be requested to ensure that subsequent
-        requests can reuse this request.
-
-        Used as part of _get_state_for_group_using_inflight_cache.
-
-        Returns:
-            Tuple of two values:
-                A sequence of ObservableDeferreds to observe
-                A StateFilter representing what else needs to be requested to fulfill the request
-        """
-
-        inflight_requests = self._state_group_inflight_requests.get(group)
-        if inflight_requests is None:
-            # no requests for this group, need to retrieve it all ourselves
-            return (), state_filter_left_over
-
-        # The list of ongoing requests which will help narrow the current request.
-        reusable_requests = []
-
-        # Iterate over existing requests in roughly biggest-first order.
-        for request_state_filter in inflight_requests:
-            request_deferred = inflight_requests[request_state_filter]
-            new_state_filter_left_over = state_filter_left_over.approx_difference(
-                request_state_filter
-            )
-            if new_state_filter_left_over == state_filter_left_over:
-                # Reusing this request would not gain us anything, so don't bother.
-                continue
-
-            reusable_requests.append(request_deferred)
-            state_filter_left_over = new_state_filter_left_over
-            if state_filter_left_over == StateFilter.none():
-                # we have managed to collect enough of the in-flight requests
-                # to cover our StateFilter and give us the state we need.
-                break
-
-        if (
-            state_filter_left_over != StateFilter.none()
-            and len(inflight_requests) >= MAX_INFLIGHT_REQUESTS_PER_GROUP
-        ):
-            # There are too many requests for this group.
-            # To prevent even more from building up, we request the whole
-            # state filter to guarantee that we can be reused by any subsequent
-            # requests for this state group.
-            return (), StateFilter.all()
-
-        return reusable_requests, state_filter_left_over
-
-    async def _get_state_for_group_fire_request(
-        self, group: int, state_filter: StateFilter
-    ) -> StateMap[str]:
-        """
-        Fires off a request to get the state at a state group,
-        potentially filtering by type and/or state key.
-
-        This request will be tracked in the in-flight request cache and automatically
-        removed when it is finished.
-
-        Used as part of _get_state_for_group_using_inflight_cache.
-
-        Args:
-            group: ID of the state group for which we want to get state
-            state_filter: the state filter used to fetch state from the database
-        """
-        cache_sequence_nm = self._state_group_cache.sequence
-        cache_sequence_m = self._state_group_members_cache.sequence
-
-        # Help the cache hit ratio by expanding the filter a bit
-        db_state_filter = state_filter.return_expanded()
-
-        async def _the_request() -> StateMap[str]:
-            group_to_state_dict = await self._get_state_groups_from_groups(
-                (group,), state_filter=db_state_filter
-            )
-
-            # Now let's update the caches
-            self._insert_into_cache(
-                group_to_state_dict,
-                db_state_filter,
-                cache_seq_num_members=cache_sequence_m,
-                cache_seq_num_non_members=cache_sequence_nm,
-            )
-
-            # Remove ourselves from the in-flight cache
-            group_request_dict = self._state_group_inflight_requests[group]
-            del group_request_dict[db_state_filter]
-            if not group_request_dict:
-                # If there are no more requests in-flight for this group,
-                # clean up the cache by removing the empty dictionary
-                del self._state_group_inflight_requests[group]
-
-            return group_to_state_dict[group]
-
-        # We don't immediately await the result, so must use run_in_background
-        # But we DO await the result before the current log context (request)
-        # finishes, so don't need to run it as a background process.
-        request_deferred = run_in_background(_the_request)
-        observable_deferred = ObservableDeferred(request_deferred, consumeErrors=True)
-
-        # Insert the ObservableDeferred into the cache
-        group_request_dict = self._state_group_inflight_requests.setdefault(
-            group, SortedDict(state_filter_rough_priority_comparator)
-        )
-        group_request_dict[db_state_filter] = observable_deferred
-
-        return await make_deferred_yieldable(observable_deferred.observe())
-
-    async def _get_state_for_group_using_inflight_cache(
-        self, group: int, state_filter: StateFilter
-    ) -> MutableStateMap[str]:
-        """
-        Gets the state at a state group, potentially filtering by type and/or
-        state key.
-
-        1. Calls _get_state_for_group_gather_inflight_requests to gather any
-           ongoing requests which might overlap with the current request.
-        2. Fires a new request, using _get_state_for_group_fire_request,
-           for any state which cannot be gathered from ongoing requests.
-
-        Args:
-            group: ID of the state group for which we want to get state
-            state_filter: the state filter used to fetch state from the database
-        Returns:
-            state map
-        """
-
-        # first, figure out whether we can re-use any in-flight requests
-        # (and if so, what would be left over)
-        (
-            reusable_requests,
-            state_filter_left_over,
-        ) = self._get_state_for_group_gather_inflight_requests(group, state_filter)
-
-        if state_filter_left_over != StateFilter.none():
-            # Fetch remaining state
-            remaining = await self._get_state_for_group_fire_request(
-                group, state_filter_left_over
-            )
-            assembled_state: MutableStateMap[str] = dict(remaining)
-        else:
-            assembled_state = {}
-
-        gathered = await make_deferred_yieldable(
-            defer.gatherResults(
-                (r.observe() for r in reusable_requests), consumeErrors=True
-            )
-        ).addErrback(unwrapFirstError)
-
-        # assemble our result.
-        for result_piece in gathered:
-            assembled_state.update(result_piece)
-
-        # Filter out any state that may be more than what we asked for.
-        return state_filter.filter_state(assembled_state)
-
     async def _get_state_for_groups(
         self, groups: Iterable[int], state_filter: Optional[StateFilter] = None
     ) -> Dict[int, MutableStateMap[str]]:
@@ -476,17 +269,31 @@ class StateGroupDataStore(StateBackgroundUpdateStore, SQLBaseStore):
         if not incomplete_groups:
             return state
 
-        async def get_from_cache(group: int, state_filter: StateFilter) -> None:
-            state[group] = await self._get_state_for_group_using_inflight_cache(
-                group, state_filter
-            )
+        cache_sequence_nm = self._state_group_cache.sequence
+        cache_sequence_m = self._state_group_members_cache.sequence
 
-        await yieldable_gather_results(
-            get_from_cache,
-            incomplete_groups,
-            state_filter,
+        # Help the cache hit ratio by expanding the filter a bit
+        db_state_filter = state_filter.return_expanded()
+
+        group_to_state_dict = await self._get_state_groups_from_groups(
+            list(incomplete_groups), state_filter=db_state_filter
         )
 
+        # Now lets update the caches
+        self._insert_into_cache(
+            group_to_state_dict,
+            db_state_filter,
+            cache_seq_num_members=cache_sequence_m,
+            cache_seq_num_non_members=cache_sequence_nm,
+        )
+
+        # And finally update the result dict, by filtering out any extra
+        # stuff we pulled out of the database.
+        for group, group_state_dict in group_to_state_dict.items():
+            # We just replace any existing entries, as we will have loaded
+            # everything we need from the database anyway.
+            state[group] = state_filter.filter_state(group_state_dict)
+
         return state
 
     def _get_state_for_groups_using_cache(