feat: set query label session property in bq session

[ncbkr]

we want to use the SQLMesh session properties to attach labels to the BigQuery jobs. Using these labels we want to enable ourselves to

• map BigQuery jobs to SQLMesh models
• map BigQuery jobs to owners/users of SQLMesh

In the model definition, this would like as follows

session_properties (
    query_label = [
      ('label1', 'value1'),
      ('label2', 'value2'),
      ('label3', 'value3')
    ]
  )

This is currently not possible in an easy way since all jobs are created by the same service account.

The screenshot below displays the information about a BigQuery job created by sqlmesh to backfill a model. In the last line you can see the label my_session_property_key: my_session_property_value. This comes from the session_properties of the sqlmesh model definition. According to the google docs for BigQuery, all jobs that are run within a session inherit the labels set at the beginning of the session using SET @@query_label = <my_labels>

[izeigerman]

I think this can also be exp.Tuple not just exp.Array. Eg:

query_labels = ['label_a', 'label_b']

vs

query_labels = ('label_a', 'label_b')

[georgesittas]

Yep, perhaps also Paren as an edge case.

[ncbkr]

Sorry for not including a usage example in the PR description. I imagined the model definition to look like this

session_properties (
    query_label = [
      ('key1', 'value1'),
      ('key2', 'value2'),
      ('key3', 'value3')
    ]
  )

I chose this format based on the google docs:

a key-value pair for the label to assign to all future queries in the session. You can also add multiple key-value pairs, separated by a comma (for example, SET @@query_label = "key1:value1,key2:value2").

Also, this is consistent with the usage of labels in both, the virtual and phyiscal properties.

This format is also why I explicitely check for an array.

What do you think about this format? Would you prefer another one?

e.g. choosing this format

query_labels = ['label_a', 'label_b'] | ('label_a', 'label_b')  # array or tuple

label_a and label_b would have to be a string following this pattern: key:value

[ncbkr]

@georgesittas would this be an edge case you had in mind?

query_labels = ('label_a')

So query_label is not a tuple or array but a single string 'key:vale' wrapped in parentheses?

[izeigerman]

The format makes sense, but it might also be:

session_properties (
    query_label = (
      ('key1', 'value1'),
      ('key2', 'value2'),
      ('key3', 'value3')
    )
  )

which would make a tuple of tuples rather than array of tuples.
Similarly

session_properties (
  query_label = (
    ('key1', 'value1')
  )
)

makes it a Paren of tuples.

[izeigerman]

what if it's an identifier and not a string literal eg: query_labels = [ label_a ] and not query_labels = [ 'label_a' ]. Might worth support both approaches.

[georgesittas]

We could simply require strings; not sure what's the value of supporting identifiers here. Seems like an unnecessary increase in scope?

[izeigerman]

I feel like this is something that should be captured at model load time and not at execution time. This seems too late.

[izeigerman]

Thanks for your contribution! Can you please add some tests.