VReplication: make flags workflow-specific and dynamically changeable

[rohit-nayak-ps]

Description

Currently several configuration options for VReplication Workflows are vttablet flags. This means that any change requires restarts of vttablets. This PR allows Workflow Update to set these flags for a specific workflow. On a workflow init the config changes are merged into the default values (which are the ones specified via the vttablet flags).

A major refactor was required to pass the config through to the various components where the vttablet flag values were directly used.

Note:

• Any change to the configuration should be made via WorkflowUpdate, otherwise the existing controllers will not pick up the new values.

Todos

• [ ] Add flags to MoveTables/Reshard
• [ ] Pass flags to VStreamer: this will be done after https://github.com/vitessio/vitess/pull/16593 is merged since that already adds options to the required APIs and mocks

Persistence

A new sub-object config has been added to the options json document column in _vt.vreplication. This is a map of key/value pairs with the key being the flag name and value a string representation of the value. Appropriate serialization and deserialization is done while storing the values and reading it back.

Related Changes

• When ever a workflow starts the controller loads the config values into its local scope
• The flag variables have been made private except for a few yet to be migrated (todo: list all)
• All code locations which accessed the flag values have been modified to use the locally scoped values
• Tests and API signature changes required a lot of related tedious code change

List of all dynamic flags

S. No.	Flag Name	Current Default Value
1	vreplication_max_time_to_retry_on_error	0s
2	vstream_dynamic_packet_size	true
3	vreplication_net_write_timeout	600
4	vreplication_heartbeat_update_interval	1
5	vreplication-parallel-insert-workers	1
6	vstream_packet_size	250000
7	vreplication_experimental_flags	3
8	vreplication_retry_delay	5s
9	relay_log_max_size	250000
10	vstream_binlog_rotation_threshold	67108864
11	vreplication_store_compressed_gtid	false
12	vreplication_net_read_timeout	300
13	vreplication_copy_phase_duration	1h
14	relay_log_max_items	5000
15	vreplication_replica_lag_tolerance	1m

Related Issue(s)

https://github.com/vitessio/vitess/issues/16489

Checklist

• [ ] "Backport to:" labels have been added if this change should be back-ported to release branches
• [ ] If this change is to be back-ported to previous releases, a justification is included in the PR description
• [ ] Tests were added or are not required
• [ ] Did the new or modified tests pass consistently locally and on CI?
• [ ] Documentation was added or is not required