Percona Monthly Bug Report: December 2020

Percona Bug Report Dec 2020Here at Percona, we operate on the premise that full-transparency makes a product better. We strive to build the best open-source database products, but also to help you manage any issues that arise in any of the databases that we support. And, in true open-source form, report back on any issues or bugs you might encounter along the way.

We constantly update our bug reports and monitor other boards to ensure we have the latest information, but we wanted to make it a little easier for you to keep track of the most critical ones. This monthly post is a central place to get information on the most noteworthy open and recently resolved bugs. 

In this December 2020 edition of our monthly bug report, we have the following list of bugs:

Percona Server for MySQL/MySQL Bugs

PS-7264 (MySQL #83799) ALTER table fails with the following error for a table with a self-referential (referring to the same table), leaving the table in an inconsistent state.

 [ERROR] InnoDB: dict_load_foreigns() returned 38 for ALTER TABLE t1

After mysqld restart accessing this table will throw a warning for missing foreign key indexes.

Affects Version/s: 5.6,5.7  [Tested/Reported version 5.6.47-87.0, 5.7.30-33]


PS-5641 (MySQL#95863): Deadlock on MTS replica while running administrative commands, caused by one of the MTS thread and administrative command thread where both are waiting for commit lock. As a result of this bug, you may see replication lag along with deadlock. This is a design flaw in the way MTS locks interact with non-replication locks like MDL or ACL locks, and the lack of deadlock detection infrastructure in replication. 

There are three ways of hitting this issue:

  • SET GLOBAL read_only=[ON/OFF]
  • SET GLOBAL super_read_only=[ON/OFF]

 Affects Version/s: 5.7,8.0  [Tested/Reported version 5.7.26, 8.0.15,8.0.20]


PS-7437 (MySQL#101716): We use Performance_Schema to check various stats while troubleshooting but you need to be careful while checking memory stats from memory_summary_by_account_by_event_name table which shows incorrect “current_number_of_bytes_used” value for events.

 Affects Version/s: 5.7,8.0  [Tested/Reported version 5.7.31-34, 8.0.21-12]


Percona XtraDB Cluster

PXC-3418: PXC Cluster node can hang when there is a concurrent read-write load on the table and there is a parallel in-place ALTER TABLE is happening on the table.

For example, case deadlock can be seen with the following steps:

  • An In-place ALTER TABLE query in one session.
  • A DML on the same table is from another session.

Affects Version/s: 5.7,8.0

Fixed version/s:  5.7.33, 8.0.21


PXC-3366: Upgrading SSL traffic enabled  PXC 5.7 to PXC 8.0 will not show any status/variable, it will give empty output always. Also, taking backup of this upgraded PXC 8.0 node using xtrabackup will fail with a crash due to this bug.

Affects Version/s: 8.0   [Tested/Reported 8.0.19]



Percona XtraBackup

PXB-2314: Percona XtraBackup 8.0.14 is not compatible with MySQL 8.0.22 due to disk format changes introduced in the 8.0.22 release. Issue fixed in xtrabackup version 8.0.22 and you should use xtrabackup 8.0.22 version for taking backup of PS/MySQL version 8.0.22 and above.

Affects Version/s:  8.0.14  

Fixed version/s:  8.0.22


PXB-2375:  In some cases, xtrabackup will write the wrong binlog filename, pos, and GTID combination info in xtrabackup_binlog_info. 

If we are using this backup with GTID position details in xtrabackup_binlog_info to create a new replica, then most likely replication will break due to incorrect GTID position.

Looks like the GTID position is not consistent with binlog file pos, they are captured differently and later printed together in xtrabackup_binlog_info  file.

Affects Version/s:  8.0 [Tested/Reported version 8.0.14]


Percona Toolkit

PT-1891: pt-mongodb-summary fails for SSL enabled MongoDB instances. It fails because pt-mongodb-summary can’t connect to SSL enabled MongoDB.

Affects Version/s:  3.1.10

Fixed Version/s: 3.3.0


PT-1747: pt-online-schema-change was bringing the database into a broken state when applying the “rebuild_constraints” foreign keys modification method if any of the child tables were blocked by the metadata lock.

Affects Version/s:  3.x   [Tested/Reported version 3.0.13]

A critical bug since it can cause data inconsistency in the user environment. It potentially affects who rebuilds tables with foreign keys. Affects those who rebuild tables with a self-referencing foreign key.


PMM  [Percona Monitoring and Management]

PMM-7092:  Upgrade to PMM 2.12.0 fails with the container in an unhealthy state.   

Upgrade process fails with following error,

/srv/victoriametrics/data with -retentionPeriod=30d: cannot create a directory for the storage at “/srv/victoriametrics/data”: mkdir /srv/victoriametrics: permission denied

Starting from PMM 2.12.0 release, it integrated with VictoriaMetricsDB and replaced Prometheus as its default method of data ingestion.

It has easy workaround as follows:

1) docker exec -ti pmm-server mkdir -p /srv/victoriametrics/data

2) docker exec -ti pmm-server chown -R pmm:pmm /srv/victoriametrics/

3)  docker restart pmm-server

Affects Version/s:  2.12.0  [Tested/Reported version 2.12.0]

Fixed Version: PMM-2.13.0


PMM-7178: PMM-PostgreSQL monitoring, pg_stat_monitor integration is broken due to a missing column in PostgreSQL.

This query fails on the PostgreSQL side because many of the columns (for example, total_calls, effected_rows, tables_names) are not existing anymore in the pg_stat_monitor view.

A bug is valid for –query-source=pgstatmonitor, with default query-source i.e pg_stat_statements we don’t see this issue.


PMM-4547: MongoDB dashboard replication lag count incorrect.

With a hidden replica (with/without any delay specified). Another replica will show a delay of the max unsigned integer value (about 136 years).

The problem here is that sometimes, MongoDB reports (in getDiagnosticData) that the primary is behind the secondary. Since timestamps are unsigned ints, subtracting a bigger number produces an overflow and that’s why we see 100+ years lag.

Affects Version/s:  2.9  [Tested/Reported version 2.0,2.9.0]

Fixed Version: PMM-2.12.0



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