From df8a3cef6b997f9eb2be7780293a64c873f7580f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dagfinn=20Ilmari=20Manns=C3=A5ker?= <ilmari@ilmari.org>
Date: Mon, 1 Jun 2020 15:23:43 +0100
Subject: [PATCH] Improve performance of _get_state_groups_from_groups_txn
(#7567)
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The query keeps showing up in my slow query log.
This changes the plan under the top-level Sort node from
```
WindowAgg (cost=280335.88..292963.15 rows=561212 width=80) (actual time=138.651..160.562 rows=27112 loops=1)
-> Sort (cost=280335.88..281738.91 rows=561212 width=84) (actual time=138.597..140.622 rows=27112 loops=1)
Sort Key: state_groups_state.type, state_groups_state.state_key, state_groups_state.state_group
Sort Method: quicksort Memory: 4581kB
-> Nested Loop (cost=2.83..226745.22 rows=561212 width=84) (actual time=21.548..47.657 rows=27112 loops=1)
-> HashAggregate (cost=2.27..3.28 rows=101 width=8) (actual time=21.526..21.535 rows=20 loops=1)
Group Key: state.state_group
-> CTE Scan on state (cost=0.00..2.02 rows=101 width=8) (actual time=21.280..21.493 rows=20 loops=1)
-> Index Scan using state_groups_state_type_idx on state_groups_state (cost=0.56..2189.40 rows=5557 width=84) (actual time=0.005..0.991 rows=1356 loops=20)
Index Cond: (state_group = state.state_group)
```
to
```
Nested Loop (cost=2.83..226745.22 rows=561212 width=84) (actual time=24.194..52.834 rows=27112 loops=1)
-> HashAggregate (cost=2.27..3.28 rows=101 width=8) (actual time=24.130..24.138 rows=20 loops=1)
Group Key: state.state_group
-> CTE Scan on state (cost=0.00..2.02 rows=101 width=8) (actual time=23.887..24.113 rows=20 loops=1)
-> Index Scan using state_groups_state_type_idx on state_groups_state (cost=0.56..2189.40 rows=5557 width=84) (actual time=0.016..1.159 rows=1356 loops=20)
Index Cond: (state_group = state.state_group)
```
This cuts the execution time from ~190ms to ~130ms, i.e. a reduction
of ~30%.
The full plans are visualised at https://explain.depesz.com/s/WpbT and
https://explain.depesz.com/s/KlEk
Signed-off-by: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
---
changelog.d/7567.misc | 1 +
synapse/storage/data_stores/state/bg_updates.py | 12 ++++++------
2 files changed, 7 insertions(+), 6 deletions(-)
create mode 100644 changelog.d/7567.misc
diff --git a/changelog.d/7567.misc b/changelog.d/7567.misc
new file mode 100644
index 0000000000..b086d5d026
--- /dev/null
+++ b/changelog.d/7567.misc
@@ -0,0 +1 @@
+Improve query performance for fetching state from a PostgreSQL database.
diff --git a/synapse/storage/data_stores/state/bg_updates.py b/synapse/storage/data_stores/state/bg_updates.py
index e8edaf9f7b..ff000bc9ec 100644
--- a/synapse/storage/data_stores/state/bg_updates.py
+++ b/synapse/storage/data_stores/state/bg_updates.py
@@ -109,20 +109,20 @@ class StateGroupBackgroundUpdateStore(SQLBaseStore):
SELECT prev_state_group FROM state_group_edges e, state s
WHERE s.state_group = e.state_group
)
- SELECT DISTINCT type, state_key, last_value(event_id) OVER (
- PARTITION BY type, state_key ORDER BY state_group ASC
- ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
- ) AS event_id FROM state_groups_state
+ SELECT DISTINCT ON (type, state_key)
+ type, state_key, event_id
+ FROM state_groups_state
WHERE state_group IN (
SELECT state_group FROM state
- )
+ ) %s
+ ORDER BY type, state_key, state_group DESC
"""
for group in groups:
args = [group]
args.extend(where_args)
- txn.execute(sql + where_clause, args)
+ txn.execute(sql % (where_clause,), args)
for row in txn:
typ, state_key, event_id = row
key = (typ, state_key)
--
GitLab