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Only join on event_labels if we're filtering on labels

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Brendan Abolivier 2019-11-07 14:55:10 +00:00
parent 15a1a02e70
commit 70804392ae
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1 changed files with 24 additions and 9 deletions
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31
synapse/storage/data_stores/main/stream.py
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@ -871,23 +871,38 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
args.append(int(limit))
# Using DISTINCT in this SELECT query is quite expensive, because it requires the
# engine to sort on the entire (not limited) result set, i.e. the entire events
# table. We only need to use it when we're filtering on more than two labels,
# because that's the only scenario in which we can possibly to get multiple times
# the same event ID in the results.
select_keywords = "SELECT"
if event_filter and event_filter.labels and len(event_filter.labels) > 1:
join_clause = ""
if event_filter and event_filter.labels:
# If we're not filtering on a label, then joining on event_labels will
# return as many row for a single event as the number of labels it has. To
# avoid this, only join if we're filtering on at least one label.
join_clause = (
"LEFT JOIN event_labels"
" USING (event_id, room_id, topological_ordering)"
)
if len(event_filter.labels) > 1:
# Using DISTINCT in this SELECT query is quite expensive, because it
# requires the engine to sort on the entire (not limited) result set,
# i.e. the entire events table. We only need to use it when we're
# filtering on more than two labels, because that's the only scenario
# in which we can possibly to get multiple times the same event ID in
# the results.
select_keywords += "DISTINCT"
sql = (
"%(select_keywords)s event_id, topological_ordering, stream_ordering"
" FROM events"
" LEFT JOIN event_labels USING (event_id, room_id, topological_ordering)"
" %(join_clause)s"
" WHERE outlier = ? AND room_id = ? AND %(bounds)s"
" ORDER BY topological_ordering %(order)s,"
" stream_ordering %(order)s LIMIT ?"
) % {"select_keywords": select_keywords, "bounds": bounds, "order": order}
) % {
"select_keywords": select_keywords,
"join_clause": join_clause,
"bounds": bounds,
"order": order
}
txn.execute(sql, args)