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Enable REPLACE INTO engine and Fix Foreign key locking issue #14532

Merged
merged 10 commits into from
Nov 20, 2023
Merged

Enable REPLACE INTO engine and Fix Foreign key locking issue #14532

merged 10 commits into from
Nov 20, 2023

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harshit-gangal
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@harshit-gangal harshit-gangal commented Nov 16, 2023 •
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Description

While adding REPLACE INTO support for foreign keys in unsharded tables, we discovered that select queries executed for foreign key cascade were not able to acquire an adequate level of lock on the unique key due to missing gap locks. This led to incorrect results, and further plan execution would result in missing cascading rows, leading to incomplete data in the binary logs.

VReplication workflow relies on these binary logs for tasks like online-ddl or change log streaming.

Example case:

drop table if exists some_table;
create table some_table (
    id bigint,
    col varchar(10),
    primary key (id),
    unique index(col)
) ;

insert into some_table(id, col) values (3, null), (4, 5);

-- Session 1
begin;
select col from some_table where col in (5) or id in (3)  for update;


-- Session 2
begin;
select col from some_table where col in (('5')) for update;
-- This should block


-- Session 1
delete from some_table where col in (5) or id in (3) ;
insert into some_table(id, col) values (3, 5);
commit;


-- Session 2
-- Unblocked but returns 0 rows
select col from some_table where col in (('5')) for update;
-- This repeatable query in Session 2 now returns 1 row
revert;

To address the issue of blocked queries not providing updated results, we tried several techniques:

  1. Locking parent rows with verification logic.
  2. Using multiple select statements to acquire the necessary lock.
  3. Employing a union statement for the lock.
  4. Implementing a self-join query to obtain the lock.

These methods worked with two threads but led to incorrect/missing binary logs in a multi-threaded system.

As a solution, we're using the NOWAIT lock to promptly acquire the lock for cascade selection. NOWAIT ensures immediate lock acquisition or failure, which may result in more foreign key-related DMLs failing, necessitating query or transaction rollback. This approach, however, effectively addresses the problem of lock waiting and prevents incorrect results.

Related Issue(s)

Checklist

  • Tests were added or are not required
  • Did the new or modified tests pass consistently locally and on the CI

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vitess-bot bot commented Nov 16, 2023

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

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@vitess-bot vitess-bot bot added NeedsDescriptionUpdate The description is not clear or comprehensive enough, and needs work NeedsIssue A linked issue is missing for this Pull Request NeedsWebsiteDocsUpdate What it says labels Nov 16, 2023
@vitess-bot vitess-bot bot mentioned this pull request Nov 16, 2023
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@github-actions github-actions bot added this to the v19.0.0 milestone Nov 16, 2023
@harshit-gangal harshit-gangal removed NeedsWebsiteDocsUpdate What it says NeedsIssue A linked issue is missing for this Pull Request NeedsDescriptionUpdate The description is not clear or comprehensive enough, and needs work labels Nov 16, 2023
@harshit-gangal harshit-gangal marked this pull request as ready for review November 16, 2023 19:19
GuptaManan100
GuptaManan100 approved these changes Nov 17, 2023
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Rest LGTM!

go/test/endtoend/vtgate/foreignkey/fk_test.go Show resolved Hide resolved
go/test/endtoend/vtgate/foreignkey/fk_test.go Outdated Show resolved Hide resolved
@harshit-gangal
addressed review comments
10a7424 
Signed-off-by: Harshit Gangal <[email protected]>
@harshit-gangal harshit-gangal merged commit 82bd8ee into vitessio:main Nov 20, 2023
115 checks passed
@harshit-gangal harshit-gangal deleted the replace-plan branch November 20, 2023 10:41
@deepthi deepthi changed the title Enable Replace Into engine and Fix Foreign key locking issue Enable REPLACE INTO engine and Fix Foreign key locking issue Nov 21, 2023
ejortegau pushed a commit to slackhq/vitess that referenced this pull request Dec 13, 2023
@harshit-gangal @shlomi-noach @ejortegau
Enable Replace Into engine and Fix Foreign key locking issue (vites…
63aadd1 
…sio#14532)

Signed-off-by: Harshit Gangal <[email protected]>
Signed-off-by: Shlomi Noach <[email protected]>
Co-authored-by: Shlomi Noach <[email protected]>
@harshit-gangal harshit-gangal mentioned this pull request Dec 13, 2023
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@systay systay systay approved these changes

@GuptaManan100 GuptaManan100 GuptaManan100 approved these changes

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