Use UPSERT when storing user mentions (!68433) · Merge requests · GitLab.org / GitLab

Heinrich Lee Yu requested to merge 338729-use-upsert-for-storing-mentions into master Aug 18, 2021

What does this MR do?

Using UPSERT saves us a query, avoids cases where we get RecordNotUnique, and removes the use of SAVEPOINT which can cause PG performance issues.

Old code

Find the associated xxx_user_mentions record (1 query)
If the new / updated Markdown has mentions, save the record. If not, destroy the record if it exists. (1 query)
If we're creating a new record in step 2, it could raise RecordNotUnique in certain race conditions. If that happens, we fetch the record and do an update (2 queries)

This uses safe_ensure_unique which uses SAVEPOINT so that we can catch the uniqueness violation and not fail the whole transaction.

New code

If the new / updated Markdown has mentions, upsert the record. If not, execute a DELETE query. (1 query)

The upsert query looks like this when creating / updating a note:

INSERT INTO "issue_user_mentions" 
  ("mentioned_users_ids", "mentioned_groups_ids", "mentioned_projects_ids", "issue_id", "note_id")
VALUES 
  ('{1}', NULL, NULL, 1, 1)
ON CONFLICT ("issue_id", "note_id")
DO UPDATE SET 
  "mentioned_users_ids"=excluded."mentioned_users_ids",
  "mentioned_groups_ids"=excluded."mentioned_groups_ids",
  "mentioned_projects_ids"=excluded."mentioned_projects_ids"
RETURNING "id"

When creating an issue / updating the description:

INSERT INTO "issue_user_mentions" 
  ("mentioned_users_ids", "mentioned_groups_ids", "mentioned_projects_ids", "issue_id", "note_id")
VALUES 
  ('{1}', NULL, NULL, 1, NULL)
ON CONFLICT ("issue_id") WHERE (note_id IS NULL)
DO UPDATE SET 
  "mentioned_users_ids"=excluded."mentioned_users_ids",
  "mentioned_groups_ids"=excluded."mentioned_groups_ids",
  "mentioned_projects_ids"=excluded."mentioned_projects_ids",
  "note_id"=excluded."note_id"
RETURNING "id"

Migration output

== 20210818055357 AddUniqueCommitDesignUserMentionIndexes: migrating ==========
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:commit_user_mentions, [:commit_id, :note_id], {:unique=>true, :name=>"commit_user_mentions_on_commit_id_and_note_id_unique_index", :algorithm=>:concurrently})
   -> 0.0043s
-- add_index(:commit_user_mentions, [:commit_id, :note_id], {:unique=>true, :name=>"commit_user_mentions_on_commit_id_and_note_id_unique_index", :algorithm=>:concurrently})
   -> 0.0052s
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:design_user_mentions, [:design_id, :note_id], {:unique=>true, :name=>"design_user_mentions_on_design_id_and_note_id_unique_index", :algorithm=>:concurrently})
   -> 0.0024s
-- add_index(:design_user_mentions, [:design_id, :note_id], {:unique=>true, :name=>"design_user_mentions_on_design_id_and_note_id_unique_index", :algorithm=>:concurrently})
   -> 0.0053s
-- transaction_open?()
   -> 0.0000s
-- indexes(:commit_user_mentions)
   -> 0.0029s
-- remove_index(:commit_user_mentions, {:algorithm=>:concurrently, :name=>"commit_id_and_note_id_index"})
   -> 0.0028s
-- transaction_open?()
   -> 0.0000s
-- indexes(:design_user_mentions)
   -> 0.0026s
-- remove_index(:design_user_mentions, {:algorithm=>:concurrently, :name=>"design_user_mentions_on_design_id_and_note_id_index"})
   -> 0.0027s
== 20210818055357 AddUniqueCommitDesignUserMentionIndexes: migrated (0.0378s) =

Down

== 20210818055357 AddUniqueCommitDesignUserMentionIndexes: reverting ==========
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:design_user_mentions, [:design_id, :note_id], {:name=>"design_user_mentions_on_design_id_and_note_id_index", :algorithm=>:concurrently})
   -> 0.0048s
-- add_index(:design_user_mentions, [:design_id, :note_id], {:name=>"design_user_mentions_on_design_id_and_note_id_index", :algorithm=>:concurrently})
   -> 0.0049s
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:commit_user_mentions, [:commit_id, :note_id], {:name=>"commit_id_and_note_id_index", :algorithm=>:concurrently})
   -> 0.0023s
-- add_index(:commit_user_mentions, [:commit_id, :note_id], {:name=>"commit_id_and_note_id_index", :algorithm=>:concurrently})
   -> 0.0038s
-- transaction_open?()
   -> 0.0000s
-- indexes(:design_user_mentions)
   -> 0.0026s
-- remove_index(:design_user_mentions, {:algorithm=>:concurrently, :name=>"design_user_mentions_on_design_id_and_note_id_unique_index"})
   -> 0.0024s
-- transaction_open?()
   -> 0.0000s
-- indexes(:commit_user_mentions)
   -> 0.0031s
-- remove_index(:commit_user_mentions, {:algorithm=>:concurrently, :name=>"commit_user_mentions_on_commit_id_and_note_id_unique_index"})
   -> 0.0024s
== 20210818055357 AddUniqueCommitDesignUserMentionIndexes: reverted (0.0357s) =

How to setup and validate locally (strongly suggested)

You can edit / create Markdown on the console and see the queries being generated. For example:

[1] pry(main)> i = Issue.first
=> #<Issue id:1 gitlab-org/gitlab-test#1>
[2] pry(main)> i.description = '@root test'
=> "@root test"
[3] pry(main)> i.save
...
  IssueUserMention Upsert (0.4ms)  INSERT INTO "issue_user_mentions" ("mentioned_users_ids","mentioned_groups_ids","mentioned_projects_ids","issue_id","note_id") VALUES ('{1}', NULL, NULL, 1, NULL) ON CONFLICT ("issue_id") WHERE (note_id IS NULL) DO UPDATE SET "mentioned_users_ids"=excluded."mentioned_users_ids","mentioned_groups_ids"=excluded."mentioned_groups_ids","mentioned_projects_ids"=excluded."mentioned_projects_ids","note_id"=excluded."note_id" RETURNING "id" /*application:console,line:/data/cache/bundle-2.7.2/ruby/2.7.0/gems/activerecord-6.1.3.2/lib/active_record/connection_adapters/postgresql/database_statements.rb:53:in `exec_query'*/
...

Does this MR meet the acceptance criteria?

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I have self-reviewed this MR per code review guidelines.
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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.

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Related to #338729 (closed)

Edited Aug 18, 2021 by Heinrich Lee Yu

Use UPSERT when storing user mentions