v16: Online DDL: enforce ALGORITHM=COPY on shadow table

[shlomi-noach]

Description

Similarly to #12436, this PR uses explicit ALGORITHM=COPY when altering Online DDL shadow tables. The shadow table is empty anyway, so there is no performance impact to using COPY. The advantage of using COPY is that Xtrabackup (at least on some versions?) has problems backing up tables created with INSTANT algorithm.

Related Issue(s)

Fixes #12517

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

Deployment Notes

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[deepthi]

Is it worth declaring the algorithm values as constants versus hard-coded strings?

[shlomi-noach]

Made as constants in sql.y and sqlparser level

[deepthi]

I added a backport label, but it seems to me that this is really only a problem with v16 (or rather, the use of a newer MySQL version). We know that v15.0.2 + MySQL 8.0.23 does not suffer from this issue, so we probably don't need to backport this to v15 after all.

[shlomi-noach]

Per https://docs.percona.com/percona-xtrabackup/8.0/em/instant.html, the issue is resolved in MySQL 8.0.32 + Percona xtrabackup 8.0.32.

Copy from said doc:

To find tables with INSTANT ADD/DROP COLUMNS run the following command:

mysql> SELECT NAME FROM INFORMATION_SCHEMA.INNODB_TABLES WHERE TOTAL_ROW_VERSIONS > 0;
+---------+
| NAME    |
+---------+
| test/t1 |
| test/t2 |
| test/t3 |
+---------+
3 rows in set (0.02 sec)

[shlomi-noach]

The unit tests are failing, over an obvious change in this PR (upper vs. lower case 'COPY), but I'm unable to find where the test happens!

2023-03-01T07:50:34.0530040Z === RUN   TestAlterTableAlgorithm
2023-03-01T07:50:34.0530208Z === RUN   TestAlterTableAlgorithm/add_column
2023-03-01T07:50:34.0530360Z     sidecardb_test.go:185: 
2023-03-01T07:50:34.0530856Z         	Error Trace:	/home/runner/work/vitess/vitess/go/vt/sidecardb/sidecardb_test.go:185
2023-03-01T07:50:34.0531101Z         	Error:      	Not equal: 
2023-03-01T07:50:34.0531382Z         	            	expected: "COPY"
2023-03-01T07:50:34.0531713Z         	            	actual  : "copy"
2023-03-01T07:50:34.0531880Z         	            	
2023-03-01T07:50:34.0532064Z         	            	Diff:
2023-03-01T07:50:34.0532389Z         	            	--- Expected
2023-03-01T07:50:34.0532682Z         	            	+++ Actual
2023-03-01T07:50:34.0532993Z         	            	@@ -1,2 +1,2 @@
2023-03-01T07:50:34.0533582Z         	            	-(sqlparser.AlgorithmValue) (len=4) "COPY"
2023-03-01T07:50:34.0534095Z         	            	+(sqlparser.AlgorithmValue) (len=4) "copy"
2023-03-01T07:50:34.0534333Z         	            	 
2023-03-01T07:50:34.0534714Z         	Test:       	TestAlterTableAlgorithm/add_column
2023-03-01T07:50:34.0534934Z === RUN   TestAlterTableAlgorithm/modify_column
2023-03-01T07:50:34.0535099Z     sidecardb_test.go:185: 
2023-03-01T07:50:34.0535549Z         	Error Trace:	/home/runner/work/vitess/vitess/go/vt/sidecardb/sidecardb_test.go:185
2023-03-01T07:50:34.0535710Z         	Error:      	Not equal: 
2023-03-01T07:50:34.0536046Z         	            	expected: "COPY"
2023-03-01T07:50:34.0536356Z         	            	actual  : "copy"
2023-03-01T07:50:34.0536582Z         	            	
2023-03-01T07:50:34.0536779Z         	            	Diff:
2023-03-01T07:50:34.0537119Z         	            	--- Expected
2023-03-01T07:50:34.0537357Z         	            	+++ Actual
2023-03-01T07:50:34.0537726Z         	            	@@ -1,2 +1,2 @@
2023-03-01T07:50:34.0538295Z         	            	-(sqlparser.AlgorithmValue) (len=4) "COPY"
2023-03-01T07:50:34.0538794Z         	            	+(sqlparser.AlgorithmValue) (len=4) "copy"
2023-03-01T07:50:34.0539024Z         	            	 
2023-03-01T07:50:34.0539315Z         	Test:       	TestAlterTableAlgorithm/modify_column
2023-03-01T07:50:34.0539573Z --- FAIL: TestAlterTableAlgorithm (0.00s)
2023-03-01T07:50:34.0539869Z     --- FAIL: TestAlterTableAlgorithm/add_column (0.00s)
2023-03-01T07:50:34.0540222Z     --- FAIL: TestAlterTableAlgorithm/modify_column (0.00s)

There is no such test TestAlterTableAlgorithm and so I believe it's auto generated. There is no such line sidecardb_test.go:185 - the file is shorter. I can't find where and how this test comes to be... 😱

[shlomi-noach]

Was working with a repo that was behind vitessio/vitess. I can reproduce the tests locally now.

[frouioui]

I think we should document this fix and the issue (#12517) as a known issue in the 16_0_0_[summary|release_notes].md files. However, this can be done in a follow-up PR in order to not overload the CI, changes to the .md files won't trigger the CI if done in a subsequent PR.

This looks good to me from my limited onlineddl knowledge point of view.

[shlomi-noach]

Release notes updated by @GuptaManan100 in #12536