Pt-table-checksum 3.7.1: SHOW REPLICAS issued against MariaDB on builds with non-default version_comment

Polyglot Projects Percona Toolkit
1

(apologies - tried to submit on Jira but I get persistent “you are not authorised” errors)

pt-table-checksum 3.7.1: SHOW REPLICAS issued against MariaDB on builds with non-default version_comment

Summary

pt-table-checksum 3.7.1 crashes with a SHOW REPLICAS syntax error against MariaDB when replica discovery falls through to the hosts recursion method. The MariaDB-flavor detection in _find_replicas_by_hosts regex-matches m/maria/i against the version_comment system variable, but distribution builds that override version_comment defeat this check. The FreeBSD ports build of MariaDB sets version_comment to FreeBSD Ports (not MariaDB Server), so detection fails and the tool issues SHOW REPLICAS — a MySQL 8.1+ statement that doesn’t exist in MariaDB.

3.5.2 was unaffected because it issued SHOW SLAVE HOSTS unconditionally.

Affected versions

  • pt-table-checksum 3.7.1 (3.7.0 likely also affected)
  • Not present in 3.5.2

Environment

  • MariaDB 10.11.16 (mariadb1011-server from FreeBSD ports)
  • FreeBSD 14.3
  • percona-toolkit 3.7.1 from FreeBSD ports
  • version = 10.11.16-MariaDB-log
  • version_comment = FreeBSD Ports

Reproduction

On a master with at least one connected replica, against a MariaDB build whose version_comment does not contain the string “MariaDB”:

$ mysql -e "SHOW VARIABLES LIKE 'version%'"
+-------------------------+----------------------+
| Variable_name           | Value                |
+-------------------------+----------------------+
| version                 | 10.11.16-MariaDB-log |
| version_comment         | FreeBSD Ports        |
...

$ pt-table-checksum --replicate-check-only
DBD::mysql::db selectall_arrayref failed: You have an error in your SQL
syntax; check the manual that corresponds to your MariaDB server version
for the right syntax to use near 'REPLICAS' at line 1
[for Statement "SHOW REPLICAS"]
at /usr/local/bin/pt-table-checksum line 5463.

Observed behaviour

Crash with SHOW REPLICAS syntax error from the leaf-level replica during recursive discovery.

Expected behaviour

The tool should detect the server as MariaDB and issue SHOW SLAVE HOSTS.

Root cause

In _find_replicas_by_hosts (bin/pt-table-checksum, around line 5449 in v3.7.1):

my $vp = VersionParser->new($dbh);
my $sql = 'SHOW REPLICAS';
my $source_name = 'source';
if ( $vp lt '8.1' || $vp->flavor() =~ m/maria/i ) {
   $sql = 'SHOW SLAVE HOSTS';
   $source_name='master';
}

VersionParser::BUILDARGS populates flavor from the version_comment MySQL variable. Detection therefore only succeeds for builds that include “MariaDB” in version_comment — typically MariaDB Server from upstream. Any downstream build that overrides version_comment (FreeBSD ports uses FreeBSD Ports; other distributions/vendors may do similar) fails the regex even though the server is unambiguously MariaDB.

Two things make the bug worse in practice:

  1. The version variable (10.11.16-MariaDB-log) reliably contains the string MariaDB regardless of distribution branding, but it isn’t consulted.
  2. Level-0 replica discovery uses processlist by default and succeeds, hiding the bug from casual inspection. pt-table-checksum then recurses into each discovered replica looking for further replicas; at the leaf level processlist returns empty and the tool falls through to the hosts method, which is where the crash occurs. On a two-node topology (one master, one replica) the recursion into the replica is what trips the bug; users on this topology may believe hosts is never used.

Suggested fix

Also test the version string for “MariaDB”:

    my $vp = VersionParser->new($dbh);
    my $sql = 'SHOW REPLICAS';
    my $source_name = 'source';
-   if ( $vp lt '8.1' || $vp->flavor() =~ m/maria/i ) {
+   if ( $vp lt '8.1'
+        || $vp->flavor()  =~ m/maria/i
+        || $vp->version() =~ m/maria/i ) {
       $sql = 'SHOW SLAVE HOSTS';
       $source_name='master';
    }

version is server-side and reliable across distribution rebrands. The same gap likely exists in other tools that use VersionParser->flavor() for MariaDB detection; a more thorough fix would be to make VersionParser itself fall back to version when version_comment doesn’t disambiguate.

Workaround

Pass --recursion-method=processlist so that _find_replicas_by_hosts is never reached. Documented behaviour of this option already calls out that hosts-based discovery is unreliable, but the failure mode in this case is a hard crash rather than missed replicas.

2

Thank you for reporting the issue. Please report it also at jira.percona.com

3

I tried to but it won’t let me. No matter what I try I get persistent “you are not authorised” errors.