ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR: duplicate key value violates unique constraint "index_namespaces_on_...

https://sentry.gitlab.net/gitlab/gitlabcom/issues/1226652/

PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_namespaces_on_name_and_parent_id"
DETAIL:  Key (name, parent_id)=(sreelakshmi.x.vathiyil.ap, 6722088) already exists.

  active_record/connection_adapters/postgresql_adapter.rb:672:in `exec_params'
    @connection.exec_params(sql, type_casted_binds)
  active_record/connection_adapters/postgresql_adapter.rb:672:in `block (2 levels) in exec_no_cache'
    @connection.exec_params(sql, type_casted_binds)
  active_support/dependencies/interlock.rb:48:in `block in permit_concurrent_loads'
    yield
  active_support/concurrency/share_lock.rb:187:in `yield_shares'
    yield
  active_support/dependencies/interlock.rb:47:in `permit_concurrent_loads'
    @lock.yield_shares(compatible: [:load]) do
...
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ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_namespaces_on_name_and_parent_id"
DETAIL:  Key (name, parent_id)=(sreelakshmi.x.vathiyil.ap, 6722088) already exists.

ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_namespaces_on_name_and_parent_id"
DETAIL:  Key (name, parent_id)=(sreelakshmi.x.vathiyil.ap, 6722088) already exists.

ZD: https://gitlab.zendesk.com/agent/tickets/148465 (GitLab Internal)