backup,restore: support backing up / restore system databases

[YuJuncen]

What problem does this PR solve?

#872 and #679.

But this doesn't allow restore stats -- because the table IDs of the stats backed up are old table IDs, we need more efforts to rewrite them to make them take effect after the restoration.

What is changed and how it works?

This PR basically implemented #679 (comment), with some difference:

• When the target table not exists, RENAME TABLE temp.xxx TO mysql.xxx would be used, for effectively restoring user tables created in mysql schema.
• The user interface is the -f (the table filter) flag. Users must specify each table they want to restore by the table filter syntax (e.g. br restore full -f '*.*' -f '!mysql.*' -f 'mysql.usertable' to restore mysql.usertable).

Check List

Tests

• Integration test

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation
  • The document points out that table filter would always ignore system tables, that isn't real after this merged.
  • The usage of this feature.

Release Note

• BR now support backing up user tables created in the mysql schema.

[YuJuncen]

/run-integration-tests

[kennytm]

rest LGTM

[YuJuncen]

ERROR 2003 (HY000): Can't connect to MySQL server on '127.0.0.1' (111) 🤔

listen tcp 0.0.0.0:10080: bind: address already in use

/run-integration-tests

[SunRunAway]

Will global variables can be restored after this PR?

Not tested, but in theory they could.

Should you add this into the objective and and let the testing cover it?

[SunRunAway]

Will global variables can be restored after this PR?

Not tested, but in theory they could.

@IANTHEREAL Please make it clear to customers.

[YuJuncen]

Will global variables can be restored after this PR?

Not tested, but in theory they could.

Should you add this into the objective and and let the testing cover it?

Done, a single value test shows that GLOBAL_VARIABLES can be restored. However, note this PR is a workaround for backup / restoring user tables created in mysql. I think it would be better to not promise any ability of backup / restoring system tables.

[3pointer]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• 3pointer
• kennytm

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[YuJuncen]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 04e0887

[SunRunAway]

Will global variables can be restored after this PR?

Not tested, but in theory they could.

Should you add this into the objective and and let the testing cover it?

Done, a single value test shows that GLOBAL_VARIABLES can be restored. However, note this PR is a workaround for backup / restoring user tables created in mysql. I think it would be better to not promise any ability of backup / restoring system tables.

We should make it clear. Because once you released it, users will rely on this feature.

[ti-srebot]

cherry pick to release-4.0 in PR #1077

[ti-srebot]

cherry pick to release-5.0 in PR #1078

[YuJuncen]

@SunRunAway I added a warning over restoring system tables in the document.

cc @3pointer Please check whether it is necessary.

[IANTHEREAL]

If the system table cannot be restored correctly (referring to the system table similar to mysql.tidb, not the user data table under the mysql database), then there is no need to provide recovery methods to avoid misuse by users and affect their business

[SunRunAway]

If the system table cannot be restored correctly, why you backup them, why you implemented this feature by this pull request?