Add -restart_before_backup parameter for vtbackup

[aquarapid]

If this flag is set, we perform a clean MySQL shutdown & startup cycle to work around xtrabackup
DDL bugs (see https://jira.percona.com/browse/PXB-2205). xtrabackup flag
-lock-ddl (which is the default) is not sufficient to fix this, and we
have run into this in real-world scenarios. See #8610

Signed-off-by: Jacques Grove [email protected]

[deepthi]

vtbackup can be run with either builtin or xtrabackup backup engine. A better place for this flag and functionality is in the xtrabackup backup engine code. That gives us two benefits:

• This functionality will become available to all uses of xtrabackup, not just via vtbackup.
• Someone using builtin backup method won't be able to make the mistake of stopping and restarting mysql twice using this flag.

[aquarapid]

Not sure I agree with this; limiting this to vtbackup only avoids someone doing the wrong thing when running xtrabackup against a live instance, and killing MySQL

[deepthi]

Not sure I agree with this; limiting this to vtbackup only avoids someone doing the wrong thing when running xtrabackup against a live instance, and killing MySQL

They would have to start vttablets with the flag for that to happen. We would still default it to false.

[deepthi]

Based on an offline discussion, I'm ok with adding this flag just to vtbackup and not vttablet.
The reasoning is that for anyone using vitess-operator, there's currently no way to pass differing xtrabackup flags through vtbackup than the standard vttablet ones; so you wouldn't be able to vary this flag depending on whether you take an offline (vtbackup) backup or an online one (vttablet). We can revisit a vttablet flag when someone is able to make that change in concert with a vitess-operator change.

@aquarapid Can you rename the flag to reflect that we are doing a stop/start and not actually executing any FLUSH statements?

[deepthi]

LGTM