Add label_applied and scope to Issuable Sla

What does this MR do?

This MR adds a new column, label_applied, to the IssuableSla model. This is used to mark that a label (Exceeded SLA) label has been applied to the related issue.

We use this boolean column to avoid enqueuing needless jobs in the IncidentManagement::IncidentSlaExceededCheckWorker. Previously, if the issue/incident was still open we would enqueue a job to add a SLA label even if the label had been applied already.

DB Migration

Up:

== 20210712052519 AddLabelAppliedIssuableClosedToIssuableSla: migrating =======
-- add_column(:issuable_slas, :label_applied, :boolean, {:default=>false, :null=>false})
   -> 0.0092s
-- add_column(:issuable_slas, :issuable_closed, :boolean, {:default=>false, :null=>false})
   -> 0.0016s
== 20210712052519 AddLabelAppliedIssuableClosedToIssuableSla: migrated (0.0109s)

== 20210714043818 AddIndexForLabelAppliedToIssuableSla: migrating =============
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:issuable_slas, :due_at, {:name=>"index_issuable_slas_on_due_at_label_applied", :where=>"label_applied = FALSE", :algorithm=>:concurrently})
   -> 0.0039s
-- execute("SET statement_timeout TO 0")
   -> 0.0005s
-- add_index(:issuable_slas, :due_at, {:name=>"index_issuable_slas_on_due_at_label_applied", :where=>"label_applied = FALSE", :algorithm=>:concurrently})
   -> 0.0193s
-- execute("RESET ALL")
   -> 0.0007s
== 20210714043818 AddIndexForLabelAppliedToIssuableSla: migrated (0.0252s) ====

Post Migration:

== 20210722042939 UpdateIssuableSlasWhereIssueClosed: migrating ===============
-- execute("UPDATE issuable_slas SET issuable_closed = TRUE WHERE issuable_slas.id IN (SELECT issuable_slas.id FROM issuable_slas INNER JOIN issues ON issues.id = issuable_slas.issue_id WHERE (issues.state_id IN (2)))")
   -> 0.0258s
== 20210722042939 UpdateIssuableSlasWhereIssueClosed: migrated (0.0259s) ======

Down:

== 20210712052519 AddLabelAppliedIssuableClosedToIssuableSla: reverting =======
-- remove_column(:issuable_slas, :issuable_closed, :boolean, {:default=>false, :null=>false})
   -> 0.0170s
-- remove_column(:issuable_slas, :label_applied, :boolean, {:default=>false, :null=>false})
   -> 0.0010s
== 20210712052519 AddLabelAppliedIssuableClosedToIssuableSla: reverted (0.0203s)

== 20210714043818 AddIndexForLabelAppliedToIssuableSla: reverting =============
-- transaction_open?()
   -> 0.0000s
-- indexes(:issuable_slas)
   -> 0.0030s
-- execute("SET statement_timeout TO 0")
   -> 0.0005s
-- remove_index(:issuable_slas, {:algorithm=>:concurrently, :name=>"index_issuable_slas_on_id_due_at_label_applied"})
   -> 0.0065s
-- execute("RESET ALL")
   -> 0.0005s
== 20210714043818 AddIndexForLabelAppliedToIssuableSla: reverted (0.0114s) ====

Post migration (no-op):
== 20210722042939 UpdateIssuableSlasWhereIssueClosed: reverting ===============
== 20210722042939 UpdateIssuableSlasWhereIssueClosed: reverted (0.0000s) ======

Queries used in worker

• Before: https://explain.depesz.com/s/6GPg
• After:
  • Outer loop: https://explain.depesz.com/s/oIQO (DB lab: https://console.postgres.ai/gitlab/gitlab-production-tunnel-pg12/sessions/5266/commands/18586)
  • Inner loop (records.to_sql): DB lab: https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/5266/commands/18587

Post-migration query with plans

• https://console.postgres.ai/gitlab/gitlab-production-tunnel-pg12/sessions/5394/commands/18813

Generate test data

ALTER TABLE "issuable_slas" ADD "label_applied" boolean DEFAULT FALSE NOT NULL
ALTER TABLE "issuable_slas" ADD "issuable_closed" boolean DEFAULT FALSE NOT NULL

exec CREATE INDEX CONCURRENTLY "index_issuable_slas_on_due_at_id_label_applied_issuable_closed" ON "issuable_slas" ("due_at", "id") WHERE label_applied = FALSE AND issuable_closed = FALSE;

INSERT INTO
  issuable_slas (issue_id, due_at, label_applied, issuable_closed)
SELECT
  id, NOW() - INTERVAL '60 days' + (random() * (INTERVAL '90 days')), (round(random()) :: int) :: boolean, (round(random()) :: int) :: boolean
FROM
  issues
WHERE
  id > (
    SELECT
      id
    FROM
      issues
    ORDER BY
      id DESC OFFSET 20000
    LIMIT
      1
  );

Screenshots or Screencasts (strongly suggested)

Does this MR meet the acceptance criteria?

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• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
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• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

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• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
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Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #335008 (closed)