Apologies, finally got around to getting some data.

In a vanilla Ussuri cluster, I ran `openstack network list` with ~1k projects and ~2k projects.
@ 1k: runtime was ~6.4 sec
@ 2k: runtime was ~17.3 sec
...

I then applied:
https://review.opendev.org/c/openstack/neutron/+/810072

*Before* the patch, sanity check on indexes:
mysql> SHOW INDEX FROM networkrbacs;
+--------------+------------+--------------------------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table        | Non_unique | Key_name                                         | Seq_in_index | Column_name   | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------------+------------+--------------------------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| networkrbacs |          0 | PRIMARY                                          |            1 | id            | A         |        1813 |     NULL | NULL   |      | BTREE      |         |               |
| networkrbacs |          0 | uniq_networkrbacs0tenant_target0object_id0action |            1 | action        | A         |           2 |     NULL | NULL   |      | BTREE      |         |               |
| networkrbacs |          0 | uniq_networkrbacs0tenant_target0object_id0action |            2 | object_id     | A         |           7 |     NULL | NULL   |      | BTREE      |         |               |
| networkrbacs |          0 | uniq_networkrbacs0tenant_target0object_id0action |            3 | target_tenant | A         |        1877 |     NULL | NULL   |      | BTREE      |         |               |
| networkrbacs |          1 | object_id                                        |            1 | object_id     | A         |           7 |     NULL | NULL   |      | BTREE      |         |               |
| networkrbacs |          1 | ix_networkrbacs_project_id                       |            1 | project_id    | A         |           1 |     NULL | NULL   | YES  | BTREE      |         |               |
+--------------+------------+--------------------------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

mysql> SHOW INDEX FROM qospolicyrbacs;
+----------------+------------+------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table          | Non_unique | Key_name                     | Seq_in_index | Column_name   | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+----------------+------------+------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| qospolicyrbacs |          0 | PRIMARY                      |            1 | id            | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| qospolicyrbacs |          0 | target_tenant                |            1 | target_tenant | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| qospolicyrbacs |          0 | target_tenant                |            2 | object_id     | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| qospolicyrbacs |          0 | target_tenant                |            3 | action        | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| qospolicyrbacs |          1 | object_id                    |            1 | object_id     | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| qospolicyrbacs |          1 | ix_qospolicyrbacs_project_id |            1 | project_id    | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
+----------------+------------+------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

mysql> SHOW INDEX FROM securitygrouprbacs;
+--------------------+------------+--------------------------------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table              | Non_unique | Key_name                                               | Seq_in_index | Column_name   | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------------------+------------+--------------------------------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| securitygrouprbacs |          0 | PRIMARY                                                |            1 | id            | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| securitygrouprbacs |          0 | uniq_securitygrouprbacs0target_tenant0object_id0action |            1 | target_tenant | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| securitygrouprbacs |          0 | uniq_securitygrouprbacs0target_tenant0object_id0action |            2 | object_id     | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| securitygrouprbacs |          0 | uniq_securitygrouprbacs0target_tenant0object_id0action |            3 | action        | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| securitygrouprbacs |          1 | object_id                                              |            1 | object_id     | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| securitygrouprbacs |          1 | ix_securitygrouprbacs_project_id                       |            1 | project_id    | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
+--------------------+------------+--------------------------------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

mysql> SHOW INDEX FROM addressscoperbacs;
+-------------------+------------+----------------------------------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table             | Non_unique | Key_name                                                 | Seq_in_index | Column_name   | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------------------+------------+----------------------------------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| addressscoperbacs |          0 | PRIMARY                                                  |            1 | id            | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| addressscoperbacs |          0 | uniq_address_scopes_rbacs0target_tenant0object_id0action |            1 | target_tenant | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| addressscoperbacs |          0 | uniq_address_scopes_rbacs0target_tenant0object_id0action |            2 | object_id     | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| addressscoperbacs |          0 | uniq_address_scopes_rbacs0target_tenant0object_id0action |            3 | action        | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| addressscoperbacs |          1 | object_id                                                |            1 | object_id     | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| addressscoperbacs |          1 | ix_addressscoperbacs_project_id                          |            1 | project_id    | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
+-------------------+------------+----------------------------------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

mysql> SHOW INDEX FROM subnetpoolrbacs;
+-----------------+------------+-------------------------------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table           | Non_unique | Key_name                                              | Seq_in_index | Column_name   | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-----------------+------------+-------------------------------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| subnetpoolrbacs |          0 | PRIMARY                                               |            1 | id            | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| subnetpoolrbacs |          0 | uniq_subnetpools_rbacs0target_tenant0object_id0action |            1 | target_tenant | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| subnetpoolrbacs |          0 | uniq_subnetpools_rbacs0target_tenant0object_id0action |            2 | object_id     | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| subnetpoolrbacs |          0 | uniq_subnetpools_rbacs0target_tenant0object_id0action |            3 | action        | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| subnetpoolrbacs |          1 | object_id                                             |            1 | object_id     | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| subnetpoolrbacs |          1 | ix_subnetpoolrbacs_project_id                         |            1 | project_id    | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
+-----------------+------------+-------------------------------------------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

There was a KeyError as LEDUC mentions; this is because Ussuri does not have revision c181bb1d89e4; I used e4e236b0e1ff instead.  It also does not have table addressgrouprbacs, so I removed that table from the PR.  I then ran `sudo -u neutron neutron-db-manage upgrade ba859d649675`.

After the patch I see indexes ix_networkrbacs_target_tenant and ix_networkrbacs_action on all tables above.

I then reran the `openstack network list` command with ~2k projects; it still took about 17.3 seconds.

So adding the indexes provides no benefit, unfortunately.