Open Stack

On Sun, Mar 31, 2019 at 10:21 PM Mohammed Naser <mnaser at vexxhost.com> wrote:
>
> Hi there,
>
> During upgrades, I've noticed that when running online_data_migrations
> with "infinite-until-done" mode, it loops over all of the migrations
> one by one.
>
> However, one of the online data migrations
> (instance_obj.populate_missing_availability_zones) makes a query that
> takes a really long time as it seems inefficient (which eventually
> results in 0, cause it already ran), which means as it loops in
> "blocks" of 50, there's almost a 2-3 to 8 minute wait in really large
> environments.
>
> The question ends up in specific:
>
> SELECT count(*) AS count_1
> FROM (SELECT instance_extra.created_at AS instance_extra_created_at,
> instance_extra.updated_at AS instance_extra_updated_at,
> instance_extra.deleted_at AS instance_extra_deleted_at,
> instance_extra.deleted AS instance_extra_deleted, instance_extra.id AS
> instance_extra_id, instance_extra.instance_uuid AS
> instance_extra_instance_uuid
> FROM instance_extra
> WHERE instance_extra.keypairs IS NULL AND instance_extra.deleted = 0) AS anon_1
>
> The explain for the DB query in this example:
>
> +------+-------------+----------------+------+---------------+------+---------+------+--------+-------------+
> | id   | select_type | table          | type | possible_keys | key  |
> key_len | ref  | rows   | Extra       |
> +------+-------------+----------------+------+---------------+------+---------+------+--------+-------------+
> |    1 | SIMPLE      | instance_extra | ALL  | NULL          | NULL |
> NULL    | NULL | 382473 | Using where |
> +------+-------------+----------------+------+---------------+------+---------+------+--------+-------------+
>
> It's possible that it can be ever worse, as this number is from
> another very-long running environments.
>
> +------+-------------+----------------+------+---------------+------+---------+------+---------+-------------+
> | id   | select_type | table          | type | possible_keys | key  |
> key_len | ref  | rows    | Extra       |
> +------+-------------+----------------+------+---------------+------+---------+------+---------+-------------+
> |    1 | SIMPLE      | instance_extra | ALL  | NULL          | NULL |
> NULL    | NULL | 3008741 | Using where |
> +------+-------------+----------------+------+---------------+------+---------+------+---------+-------------+
>
> I'm not the SQL expert, could we not optimize this?  Alternatively,
> could we update the online data migrations code to "pop out" any of
> the migrations that return 0 for the next iteration, that way it only
> works on those online_data_migrations that *have* to be done, and
> ignore those it knows are done?

and while we're at it, can we just bump the default rows-per-run to
something more than
50 rows? it seems super .. small :)

> Thanks,
> Mohammed
>
> --
> Mohammed Naser — vexxhost
> -----------------------------------------------------
> D. 514-316-8872
> D. 800-910-1726 ext. 200
> E. mnaser at vexxhost.com
> W. http://vexxhost.com



-- 
Mohammed Naser — vexxhost
-----------------------------------------------------
D. 514-316-8872
D. 800-910-1726 ext. 200
E. mnaser at vexxhost.com
W. http://vexxhost.com