VReplication: Add ability to tag workflows

[rohit-nayak-ps]

Description

Users have requested the ability to group workflows. Some use cases:

• Sharded->sharded Reshards that are done incrementally, one per source shard, for reducing the risk when workflows have fatal failure and need to be restarted from scratch
• Materialize streams that require custom filters (for PII implementations, say) for each table
• When multiple tables are to be moved and these are split across workflows for performance reasons to work around the current limitation where tables are only copied one at a time per workflow

This PR adds the ability to tag workflows in a simple and extensible way. It adds a tags column to the _vt.vreplication table. Adding multiple tags is left as an implementation detail: the most obvious way would be to use a list of comma-separated tags in that column.

This implementation also allows users to tag each stream in a workflow separately by specifying separate list of tags for each stream in the workflow on each target.

To add tags at the workflow level use the Workflow command thus: vtctlclient Workflow customer.cust2cust tags 'a,b' to set the tags. Specify an empty string to reset the tags.

To set tags at the stream level use VReplicationExec thus: vtctlclient VReplicationExec zone1-100 "update _vt.vreplication set tags = 'a,b' where workflow = 'cust2cust' and keyspace = 'customer'"

The wrangler function wr.WorkflowTagAction(ctx, keyspace, workflow, tags) can be used for programmatically setting it in, say, vtadmin.

Note that tags do not affect the core functionality of vreplication workflows.

Signed-off-by: Rohit Nayak [email protected]

Checklist

• Tests were added or are not required
• Documentation was added or is not required

[ajm188]

this is looking good to me! a comment about cli, and then also about keeping the new apis in sync (which, yes, we should unify soon, but for now)

[ajm188]

Just one small thing about the protobuf type change and then this lgtm whenever you want to move out of draft

[rohit-nayak-ps]

Just one small thing about the protobuf type change and then this lgtm whenever you want to move out of draft

Ready for review

[ajm188]

lgtm