Remove non-unique index on MR metrics

What does this MR do?

This MR removes a redundant index from merge_request_metrics table (merge_request_id). After deduplicating the table, a unique index was created to support the merge_request_id column (!29566 (merged)).

• Index to remove: "index_merge_request_metrics" btree (merge_request_id)
• Index to keep (new): "unique_merge_request_metrics_by_merge_request_id" UNIQUE, btree (merge_request_id)

Migrations

up:

== 20200707071941 DropOldNonUniqueIndexOnMrMetrics: migrating =================
-- transaction_open?()
   -> 0.0000s
-- indexes(:merge_request_metrics)
   -> 0.0033s
-- remove_index(:merge_request_metrics, {:algorithm=>:concurrently, :name=>"index_merge_request_metrics"})
   -> 0.0016s
== 20200707071941 DropOldNonUniqueIndexOnMrMetrics: migrated (0.0052s) ========

down:

== 20200707071941 DropOldNonUniqueIndexOnMrMetrics: reverting =================
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:merge_request_metrics, :merge_request_id, {:name=>"index_merge_request_metrics", :algorithm=>:concurrently})
   -> 0.0032s
-- add_index(:merge_request_metrics, :merge_request_id, {:name=>"index_merge_request_metrics", :algorithm=>:concurrently})
   -> 0.0125s
== 20200707071941 DropOldNonUniqueIndexOnMrMetrics: reverted (0.0160s) ========

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• [-] Separation of EE specific content

Availability and Testing

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] 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

changed milestone to %13.2

added database databasereview pending labels

Reviewer roulette

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Category	Reviewer	Maintainer
database	Allison Browne (@allison.browne) (UTC-5, 7 hours behind @ahegyi)	Mayra Cabrera (@mayra-cabrera) (UTC-5, 7 hours behind @ahegyi)

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Generated by Danger

added typefeature label

added backstage [DEPRECATED] label and removed typefeature label

changed the description

added 1 commit

• 8aee1d26 - Remove non-unique index on MR metrics

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unmarked as a Work In Progress

added 66 commits

• 8aee1d26...c0d64fc8 - 65 commits from branch master
• fb03ff3a - Remove non-unique index on MR metrics

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marked the checklist item Changelog entry as completed

Hi @nmilojevic1,

Can you do the DB review?

assigned to @nmilojevic1

added 23 commits

• fb03ff3a...1e691756 - 22 commits from branch master
• 7c510720 - Remove non-unique index on MR metrics

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LGTM @mayra-cabrera can you please do the maintainer review.

assigned to @mayra-cabrera

added databasereviewed label and removed databasereview pending label

approved this merge request

unassigned @nmilojevic1

approved this merge request

changed the description

enabled an automatic merge when the pipeline for 98a2e355 succeeds

added databaseapproved label and removed databasereviewed label

Thanks @ahegyi! This LGTM, MWPS set

merged

mentioned in commit 339932cb

added workflowstaging label

added workflowcanary label and removed workflowstaging label

added workflowproduction label and removed workflowcanary label