MDEV-40122: +DEFAULT is not a valid value for master_heartbeat_period

[prathamesh04]

Summary

CHANGE MASTER TO master_heartbeat_period= +DEFAULT; was accepted as valid syntax (equivalent to = DEFAULT). It now produces a syntax error again.

This is a mismerge of MDEV-38454 into MDEV-28302:

• MDEV-28302 changed the rule to MASTER_HEARTBEAT_PERIOD_SYM '=' num_or_default, adding DEFAULT support.
• MDEV-38454 added opt_plus (to allow values like +60) on top of it, resulting in opt_plus num_or_default, which also accepts +DEFAULT.

Fix

Move opt_plus into num_or_default's definition in sql/sql_yacc.yy, so the + prefix may only precede a numeric literal:

• num_or_default := opt_plus NUM_literal | DEFAULT

master_heartbeat_period= +45 and = DEFAULT still work; +DEFAULT is rejected with ER_PARSE_ERROR.

Note: 11.4 and 11.8 use opt_plus NUM_literal (no DEFAULT at all), so they are not affected; the bug only exists on the 12.x line.

Test

Extended mysql-test/main/change_master_default.test (the MDEV-28302 test) with a regression case for +DEFAULT. The +-with-a-number and DEFAULT cases are already covered by MDEV-38454's rpl_heartbeat_basic and earlier in this file respectively. Verified with:

./mariadb-test-run.pl --suite=main change_master_default ps_change_master

Both tests pass (the generated parser is rebuilt from sql_yacc.yy at build time).

Jira: https://jira.mariadb.org/browse/MDEV-40122

This contribution is licensed under the 3-clause BSD license.

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All committers have signed the CLA.

[prathamesh04]

Hi @LinuxJedi, could you please take a look? This is a small parser fix for MDEV-40122, a mismerge of MDEV-38454 into MDEV-28302, with a regression test in main.change_master_default. Thanks!

[ParadoxV5]

I’m quite certain that LinuxJedi doesn’t work at MariaDB anymore.

[vuvova]

Agree. Why should +DEFAULT work? Logically, the syntax can be either

• value literal
• DEFAULT keyword
• expression

It seems that master_heartbeat_period accepts the first two, a literal number and a DEFAULT keyword. It doesn't support expressions. +5 is still a literal number, so must be recognized. But +DEFAULT is neither, not a number, not a DEFAULT, it's not even a valid expression. It's a syntactically incorrect from any point of view and it's not supported anywhere (except in INSERT where both expressions are supported and DEFAULT is a valid expression)

[gkodinov]

Thank you for your contribution! This is a preliminary review.

LGTM. Please stand by for the final review.

[gkodinov]

LGTM. Please keep working with the final reviewer.

[ParadoxV5]

Thanks @prathamesh04; please see my comments.

[ParadoxV5]

Frankly, I’d suggest avoiding breaking num_or_default back to NUM_literal and DEFAULT cases, and instead move the opt_plus under num_or_default’s definition.
But gkodinov and vuvova have already pushed the dissolution of num_or_default.

It’s true that master_heartbeat_period is the only decimal option in CHANGE MASTER, even in the foreseeable future.
But the motivation behind the X_or_defaults (at least the other ones) is to avoid repeating the MASTER_HEARTBEAT_PERIOD_SYM part of the definition, once for the explicit value and once for DEFAULT.
The ideal design was to pass both values and DEFAULTs uniformly to the options themselves… but the path to it turned out to be a lot longer than I could cram when working on MDEV-28302.

Inlining num_or_default’s branches into master_heartbeat_period’s definition also makes a seemingly complex change in contrast to moving the opt_plus.

[prathamesh04]

Done — opt_plus is now part of num_or_default (num_or_default := opt_plus NUM_literal | DEFAULT), and the action code in master_def stays unified. Thanks for the suggestion.

[vuvova]

Oh. Okay. When I first saw the description of this issue — before I looked at the code — I did a fix locally exactly this way, moving opt_plus into num_or_default. But then I saw your first fix and I kind of liked how small and simple the DEFAULT branch became and I thought your fix was better.

Well, anyway, no need to redo it again. Keep it the way @ParadoxV5 wants, it's his code after all.

[ParadoxV5]

It’s already hard to tell apart someone who agreed after consideration and a yes-man, and these days it’s even harder with 96%-AI vibers in the mix, innit?
Offence not intended; I’m just sombre about the downhill trend as an honest associate dev.

In plainer language:
My suggestion was less about “what I want”, but more to prompt thought on whether the simplicity of the separated branches outweighs num_or_default’s consolidation.

[prathamesh04]

Thanks for being direct about it — that's fair, and the design question deserves a real answer rather than a quick "done".

I did weigh the two forms before settling. The separated branches (opt_plus NUM_literal / DEFAULT inline in master_def, no num_or_default) are more explicit and would sidestep the $$-initialization trap entirely. What kept me on the consolidated form is that master_def already uses the same X_or_default pattern for its other options, so keeping num_or_default makes the heartbeat branch read like the rest of the grammar instead of being the odd one out. Both are defensible; I chose consistency over brevity, and I'm comfortable with that trade-off.

And to be plain about the yes-man part — none taken, and I'd rather earn the approval than have it handed over. The buildbot crash was mine: moving opt_plus into num_or_default left $$ uninitialized, and I should have caught that before CI did. I verified the fix against the full grammar with bison 3.7.5 and 3.8.2 and on the builder that originally crashed, so this version is the result of checking, not of agreeing.

If you have a concrete reason the separated form is better I'll switch to it; otherwise I'd like to keep the consolidated one.

[ParadoxV5]

These are unnecessary, right?

• MDEV-38454’s test (should) cover master_heartbeat_period= +45.
• master_heartbeat_period= DEFAULT is earlier in this file.

(Not to mention the additional connection setup.)

[prathamesh04]

Done — removed the +45/DEFAULT positive checks and the mdev40122 connection setup; the test now only keeps the +DEFAULT regression case. The +45 case is covered by MDEV-38454's rpl_heartbeat_basic and DEFAULT by this file earlier, as you noted.

[gkodinov]

There seems to be a crash in buildbot. Please rectify.

[prathamesh04]

Hi @gkodinov — the crash is fixed and the buildbot builder that crashed now passes.

Root cause. The fix for MDEV-40122 folded opt_plus into num_or_default, which turned the numeric alternative from a single-symbol RHS into a two-symbol one:

num_or_default: opt_plus NUM_literal { DBUG_ASSERT($$); }

bison injects a default $$ = $1 only for single-symbol RHS. With the two-symbol opt_plus NUM_literal it no longer does, so $$ was uninitialized. In an assert build the DBUG_ASSERT($$) fires; in a release build the uninitialized pointer is dereferenced at $3->val_decimal(&decimal_buf) in master_def, producing the SIGSEGV seen on amd64-debian-12 (builder 555).

Fix (commit b7640ff). Set the value explicitly:

num_or_default: opt_plus NUM_literal { DBUG_ASSERT($2); $$= $2; }
              | DEFAULT            { $$= nullptr; }

Verified by reprocessing the full grammar with the repo's gen_yy_files.cmake under bison 3.7.5 and 3.8.2 (both exit 0, no conflicts), and builder 555 (amd64-debian-12) now passes its nm test run (build 24522).

Remaining red check. The only failing check is amd64-windows-packages (builder 239, build 44948), and that failure is unrelated to this change. main.change_master_default failed once, only on retry attempt 1, at the pre-existing, unchanged --master-heartbeat-period=0.000499 block. On that attempt the restart server started without the restart parameters — there is no master-heartbeat-period rounded to 0 warning and no --skip-slave-start note in its error log, and the slave threads auto-started (emitting [ERROR] 1593), so slave_heartbeat_period read as the default 60.000 instead of 0.000. Attempts 2 and 3 applied the parameters correctly and passed (retry-pass); the step still exited non-zero only because the un-suppressed [ERROR] 1593 lines are flagged by MTR's shutdown-log check. This is a flaky MTR restart race on Windows in test code identical to base 12.3 — it does not exercise the grammar path this PR changes.

I'd rather not touch that unchanged base test section for an unrelated flake, but if you'd prefer the check to be deterministic I can make the block robust instead.

[ParadoxV5]

It’s already hard to tell apart someone who agreed after consideration and a yes-man, and these days it’s even harder with 96%-AI vibers in the mix, innit?
Offence not intended; I’m just sombre about the downhill trend as an honest associate dev.

In plainer language:
My suggestion was less about “what I want”, but more to prompt thought on whether the simplicity of the separated branches outweighs num_or_default’s consolidation.