[FeatureFlag] Enable `--batch-command` for git-cat-file(1)

What

Enable the :catfile_batch_command feature flag. The flag will enable the usage of the --batch-command flag of git-cat-file(1). This means instead of relying on --batch-check for info and --batch for content of objects, we'll use --batch-command for both.

Owners

• Team: Gitaly
• Most appropriate slack channel to reach out to: #g_gitaly
• Best individual to reach out to: NAME

Expectations

No issues to arise from the switch. The catfile package and operations form the base of multiple RPCs.

What release does this feature occur in first?

16.2

What are we expecting to happen?

We expect no issues to arise in any of the RPCs that we have

What might happen if this goes wrong?

We toggle the featureflag and fallback to previous implementation.

What can we monitor to detect problems with this?

Since it affects most RPCs we should keep an eye out on the error rate for the Gitaly service. https://dashboards.gitlab.net/d/gitaly-main/gitaly-overview?orgId=1

Roll Out Steps

• Enable on staging
  • Is the required code deployed on staging? (howto)
  • Enable on staging (howto)
  • Add featureflagstaging to this issue (howto)
  • Test on staging (howto)
  • Verify the feature flag was used by checking Prometheus metric gitaly_feature_flag_checks_total
• Enable on production
  • Is the required code deployed on production? (howto)
  • Enable on production in #production (howto)
  • Add featureflagproduction to this issue
  • Verify the feature flag was used by checking Prometheus metric gitaly_feature_flag_checks_total
• Default-enable the feature flag (optional, only required if backwards-compatibility concerns exist)
  • Wait for release containg default-disabled feature flag.
  • Change the feature flag to default-enabled (howto)
  • Wait for release containing default-enabled feature flag.
• Remove feature flag
  • Remove the feature flag and the pre-feature-flag code (howto)
  • Remove the feature flag via chatops (howto)
  • Update minimum git version
  • Remove old code
  • Annotate the errors returned in object_reader.go
  • Close this issue

Please refer to the documentation of feature flags for further information.