Fix: convertBoolToSemiSyncAction method to account for all semi sync actions #90
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Not actually going to merge this, just creating the PR here first to get some feedback internally, check that CI passes. Then will try to upstream the change. |
go/vt/mysqlctl/replication.go
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| @@ -767,3 +767,11 @@ func (mysqld *Mysqld) SemiSyncReplicationStatus() (bool, error) { | |||
| } | |||
| return false, nil | |||
| } | |||
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| func (mysqld *Mysqld) SemiSyncExtensionLoaded() bool { | |||
| qr, err := mysqld.FetchSuperQuery(context.TODO(), "SHOW GLOBAL VARIABLES LIKE 'rpl_semi_sync%'") | |||
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An improvement would be to check the INFORMATION_SCHEMA.PLUGINS meta table to check for extension being loaded. It is more performant (showing global variables is an expensive operation) and another reason being that, according to Jeremy, all SHOW ... queries are deprecated.
Here's a query you can plug in easily:
mysql> select count(*) > 0 as plugin_loaded from information_schema.plugins where plugin_name like "rpl_semi_sync_%";
+---------------+
| plugin_loaded |
+---------------+
| 0 |
+---------------+
1 row in set (0.00 sec)
plugin_loaded will be either 0 or 1
See:
https://dev.mysql.com/doc/refman/8.0/en/information-schema-plugins-table.html
and
https://dev.mysql.com/doc/refman/8.0/en/replication-semisync-installation.html
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| // Unload semi sync plugins | ||
| for _, tablet := range tablets[0:4] { | ||
| qr := utils.RunSQL(ctx, t, "select @@global.super_read_only", tablet) | ||
| result := fmt.Sprintf("%v", qr.Rows[0][0].ToString()) |
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I rebased to main and now the replicas start with super_read_only, which forbids us to uninstall plugins.
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Looks great!! I think this is definitely ready to be released/staged as a Shopify hotfix
In terms of submitting upstream, this is a nitpick but I think the level of abstraction of the test (end-to-end testing ChangeTabletType) doesn't match the level of abstraction of the change itself very well (how we interpret a false value).
| @@ -405,6 +405,41 @@ func TestCrossCellDurability(t *testing.T) { | |||
| } | |||
| } | |||
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| // Tests that ChangeTabletType works even when semi-sync plugins are not loaded. | |||
| func TestChangeTypeWithoutSemiSync(t *testing.T) { | |||
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If we are submitting upstream, I must say that it's a bit weird to have this be the only test. Maybe we could add a unit test (on the tablet manager) when submitting?
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Fair point, I'll add an unit test.
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Took a look again. I don't think a unit test would fit in this scenario, as there's not much to unit test. Unit tests in this package use the fakemysqlddaemon to mock the Mysqld type that has the SemiSyncExtensionLoaded call.
Because of that, it limits the ability of what we are testing. A unit test in mysqlctl won't actually help us test any of the changes we made.
Fakemysqldaemon also mocks a bunch of other semi sync related methods that would otherwise break without my change.
Unit tests within this codebase in general seem to abstract away interactions with the DB. I think the endtoend cluster test is the right place for our tests, and that this test offers sufficient coverage for this change. I'll push this upstream, and if I get any feedback related to testing I'll make the change then.
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👋 Hey friends! We've run into the same issue as well. If there's anything we can do to help get this upstreamed, please let me know. 🙇♂️ |
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Hey Arthur, thanks for stopping by our fork. The upstream PR for this has been approved but William is digging into some suspect test failures here: vitessio#12914 |
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This PR is being marked as stale because it has been open for 30 days with no activity. To rectify, you may do any of the following:
If no action is taken within 7 days, this PR will be closed. |
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This PR was closed because it has been stale for 7 days with no activity. |
Description
Fixes a bug where
ChangeTabletTypewould fail on clusters that don't haverpl_semi_sync_masterandrpl_semi_sync_slaveplugins loaded. Does so by refactoring theconvertBoolToSemiSyncActionmethod to returnSemiSyncActionNoneif the plugin is not loaded. To do this, we query the underlying mysql to check if therpl_semi_sync_%variables are present.Checklist
Deployment Notes