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Add an index on lower(name) to users to speed up username availability checks #20369

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Add an index on lower(name) to users to speed up username availability checks #20369

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4ec9764
Add a `users_lower_name` index on `lower(name)` to `users`
barodeur Oct 16, 2026
3c16af1
Rename changelog entry to the PR number
barodeur Oct 16, 2026
a0bbba9
Remove the tests for the users_lower_name index
barodeur Oct 16, 2026
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1 change: 1 addition & 0 deletions changelog.d/20369.misc
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Add an index on `lower(name)` to the `users` table, to speed up checking whether a username is available.
7 changes: 7 additions & 0 deletions synapse/storage/databases/main/registration.py
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Expand Up @@ -2611,6 +2611,13 @@ def __init__(
columns=["creation_ts"],
)

self.db_pool.updates.register_background_index_update(
"users_lower_name",
index_name="users_lower_name",
table="users",
columns=["lower(name)"],
)
Comment on lines +2614 to +2619

@sandhose sandhose Oct 16, 2026

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I was a little concerned that on m.org we would first drop the existing index then spend 20min recreating it, and have to do seq scan during that time. To avoid this, I renamed the index on Matrix.org, and we'll need to remember to remove it later:

ALTER INDEX users_lower_name RENAME TO temp_quenting_pr20369_users_lower_name;


self.db_pool.updates.register_background_update_handler(
"users_set_deactivated_flag", self._background_update_set_deactivated_flag
)
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18 changes: 18 additions & 0 deletions synapse/storage/schema/main/delta/95/02_users_lower_name_index.sql
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@@ -0,0 +1,18 @@
--
-- This file is licensed under the Affero General Public License (AGPL) version 3.
--
-- Copyright (C) 2026 Element Creations Ltd
--
-- This program is free software: you can redistribute it and/or modify
-- it under the terms of the GNU Affero General Public License as
-- published by the Free Software Foundation, either version 3 of the
-- License, or (at your option) any later version.
--
-- See the GNU Affero General Public License for more details:
-- <https://www.gnu.org/licenses/agpl-3.0.html>.

-- Add an index on `lower(name)` to `users`, so that case-insensitive user ID
-- lookups (e.g. when checking whether a username is available) don't need to
-- scan the whole table.
INSERT INTO background_updates (ordering, update_name, progress_json) VALUES
(9502, 'users_lower_name', '{}');
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