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1 changed files with 22 additions and 10 deletions
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@ -90,7 +90,15 @@ class StateGroupBackgroundUpdateStore(SQLBaseStore):
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state_filter: Optional[StateFilter] = None,
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) -> Mapping[int, StateMap[str]]:
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"""
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TODO
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Given a number of state groups, fetch the latest state for each group.
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Args:
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txn: The transaction object.
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groups: The given state groups that you want to fetch the latest state for.
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state_filter: The state filter to apply the state we fetch state from the database.
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Returns:
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Map from state_group to a StateMap at that point.
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"""
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state_filter = state_filter or StateFilter.all()
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@ -102,13 +110,11 @@ class StateGroupBackgroundUpdateStore(SQLBaseStore):
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# a temporary hack until we can add the right indices in
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txn.execute("SET LOCAL enable_seqscan=off")
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# The below query walks the state_group tree so that the "state"
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# The query below walks the state_group tree so that the "state"
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# table includes all state_groups in the tree. It then joins
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# against `state_groups_state` to fetch the latest state.
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# It assumes that previous state groups are always numerically
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# lesser.
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# This may return multiple rows per (type, state_key), but last_value
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# should be the same.
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sql = """
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WITH RECURSIVE sgs(state_group, state_group_reached) AS (
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VALUES(?::bigint, NULL::bigint)
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@ -214,13 +220,19 @@ class StateGroupBackgroundUpdateStore(SQLBaseStore):
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ORDER BY type, state_key, state_group DESC
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"""
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# We can sort from smallest to largest state_group and re-use the work from
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# the small state_group for a larger one if we see that the edge chain links
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# We can sort from least to greatest state_group and re-use the work from a
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# lesser state_group for a greater one if we see that the edge chain links
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# up.
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#
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# What this means in practice is that if we fetch the latest state for
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# `state_group = 20`, and then we want `state_group = 30`, it will traverse
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# down the edge chain to `20`, see that we linked up to `20` and bail out
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# early and re-use the work we did for `20`.
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sorted_groups = sorted(groups)
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state_groups_we_have_already_fetched: Set[int] = set(
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# We default to `[-1]` just to fill in the query with something
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# that will have no effect but not bork our query when it would be empty otherwise
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# We default to `[-1]` just to fill in the query with something that
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# will have no effect but not bork our query when it would be empty
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# otherwise
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[-1]
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)
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for group in sorted_groups:
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@ -244,7 +256,7 @@ class StateGroupBackgroundUpdateStore(SQLBaseStore):
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# The first row is always our special `state_group_reached` row which
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# tells us if we linked up to any other existing state_group that we
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# already fetched and if so, which one we linked up to (see the `UNION
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# ALL` above)
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# ALL` above which drives this special row)
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first_row = txn.fetchone()
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if first_row:
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_, _, _, state_group_reached = first_row
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@ -255,7 +267,7 @@ class StateGroupBackgroundUpdateStore(SQLBaseStore):
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key = (intern_string(typ), intern_string(state_key))
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partial_state_map_for_state_group[key] = event_id
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# If we see a state group edge link to a previous state_group that we
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# If we see a state_group edge link to a previous state_group that we
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# already fetched from the database, link up the base state to the
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# partial state we retrieved from the database to build on top of.
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if state_group_reached in results:
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