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MDEV-16335: Include deadlock detail information in SHOW WARNINGS #4492

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MDEV-16335: Include deadlock detail information in SHOW WARNINGS #4492

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@varundeepsaini varundeepsaini commented Dec 22, 2025 •
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  • The Jira issue number for this PR is: MDEV-16335

Description

Currently, deadlock information is only available globally via SHOW ENGINE INNODB STATUS, so a client can never be certain that the information shown is for their own session's deadlock.

This patch stores deadlock information in the victim transaction's structure when a deadlock is detected, making it accessible via SHOW WARNINGS.

Implementation

  • Added deadlock_info fields to trx_lock_t to store per-session deadlock information
  • In Deadlock::report(), copy deadlock info to the victim transaction (only when srv_print_all_deadlocks is set)
  • In convert_error_code_to_mysql(), push deadlock info as a warning via push_warning_printf()
  • Clear deadlock info when a new transaction starts or when the transaction is freed

Release Notes

When innodb_print_all_deadlocks=ON, deadlock detail information is now available per-session via SHOW WARNINGS after a deadlock error (ER_LOCK_DEADLOCK).

How can this PR be tested?

./mtr --suite=innodb deadlock_session_info

Basing the PR against the correct MariaDB version

  • This is a new feature and the PR is based against the main branch.

PR quality check

  • I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
  • For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.

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CLAassistant commented Dec 22, 2025 •
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All committers have signed the CLA.

FooBarrior
FooBarrior requested changes Dec 22, 2025
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@varundeepsaini varundeepsaini marked this pull request as draft December 22, 2025 19:46
FooBarrior
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FooBarrior
FooBarrior reviewed Dec 22, 2025
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FooBarrior
FooBarrior reviewed Dec 22, 2025
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@varundeepsaini varundeepsaini force-pushed the MDEV-16335-deadlock-info-show-warnings branch 3 times, most recently from 67920e9 to 19592c6 Compare December 22, 2025 21:23
dr-m
dr-m reviewed Dec 23, 2025
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grooverdan
grooverdan reviewed Dec 23, 2025
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@varundeepsaini varundeepsaini force-pushed the MDEV-16335-deadlock-info-show-warnings branch from 63a7517 to 0cf376f Compare December 24, 2025 05:04
@varundeepsaini varundeepsaini marked this pull request as ready for review December 24, 2025 05:22
FooBarrior
FooBarrior requested changes Dec 24, 2025
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FooBarrior
FooBarrior requested changes Dec 24, 2025
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FooBarrior
FooBarrior reviewed Dec 25, 2025
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@gkodinov gkodinov added the External Contribution All PRs from entities outside of MariaDB Foundation, Corporation, Codership agreements. label Dec 29, 2025
FooBarrior
FooBarrior approved these changes Jan 19, 2026
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Looks good to me.

dr-m
dr-m requested changes Jan 19, 2026
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The test for this functionality is only executed in debug-instrumented builds. I think that new functionality had better tested with all builds, so that the functionality will be better covered. For example, GNU/Linux distributions that package MariaDB themselves will likely not use CMAKE_BUILD_TYPE=Debug at all. We should test what we ship.

janlindstrom
janlindstrom reviewed Jan 19, 2026
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FooBarrior
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storage/innobase/lock/lock0lock.cc Outdated
static_cast<size_t>(len),
lock_latest_err_file);
ut_ad(deadlock_info_len <= static_cast<size_t>(len));
if (deadlock_info[deadlock_info_len - 1] == '\n')
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@FooBarrior FooBarrior Jan 19, 2026

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this will crash if deadlock_info_len is 0

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FooBarrior commented Jan 19, 2026

You didn't check

I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.

@varundeepsaini varundeepsaini force-pushed the MDEV-16335-deadlock-info-show-warnings branch from 4f63d11 to 5a59a74 Compare January 21, 2026 19:31
dr-m
dr-m reviewed Jan 22, 2026
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@varundeepsaini varundeepsaini requested a review from dr-m January 23, 2026 08:17
FooBarrior
FooBarrior requested changes Jan 26, 2026
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storage/innobase/lock/lock0lock.cc
static_cast<size_t>(len),
lock_latest_err_file);
ut_ad(deadlock_info_len <= static_cast<size_t>(len));
if (deadlock_info_len && deadlock_info[deadlock_info_len - 1] == '\n')
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This one is still not resolved:

this will crash if deadlock_info_len is 0

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@dr-m dr-m Jan 27, 2026

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Where would it crash? The dereferencing deadlock_info[deadlock_info_len - 1] is guarded by a check that deadlock_info_len is nonzero.

@varundeepsaini
Include deadlock detail information in SHOW WARNINGS after deadlock d…
c899cd9 
…etection error
@varundeepsaini
Added the global env condition and simplified the tests
77d377f 
Signed-off-by: Varun Deep Saini <varun.23bcs10048@ms.sst.scaler.com>
@varundeepsaini
Resolved comments
c6ed814
@varundeepsaini
remove non functional changes
58acf24
@varundeepsaini
Updated tests
bc5cf24
@varundeepsaini
resolved comments
f76cb09
@varundeepsaini
refactoring
b94f90f
@varundeepsaini
Added a new test for non debug builds
d7d77d2 
Signed-off-by: Varun Deep Saini <varun.23bcs10048@ms.sst.scaler.com>
@varundeepsaini
updated tests
62a330c 
Signed-off-by: Varun Deep Saini <varun.23bcs10048@ms.sst.scaler.com>
@varundeepsaini
reverted comments
374a9d7 
Signed-off-by: Varun Deep Saini <varun.23bcs10048@ms.sst.scaler.com>
@varundeepsaini varundeepsaini force-pushed the MDEV-16335-deadlock-info-show-warnings branch from 11ae15e to 374a9d7 Compare January 28, 2026 05:05
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@Thirunarayanan Thirunarayanan Awaiting requested review from Thirunarayanan

@janlindstrom janlindstrom Awaiting requested review from janlindstrom

@dr-m dr-m Awaiting requested review from dr-m

@FooBarrior FooBarrior Awaiting requested review from FooBarrior

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@varundeepsaini @CLAassistant @FooBarrior @grooverdan @janlindstrom @dr-m @gkodinov