Saturday, July 28, 2018

Fun with Bugs #69 - On Some Public Bugs Fixed in MySQL 5.7.23

Several MySQL releases happened yesterday, but of them all I am mostly interested in MySQL 5.7.23, as MySQL 5.7 (either directly or indirectly, via forks and upstream fixes they merge) is probably the most widely used MySQL GA release at the moment.

In this post (in a typical manner for this "Fun with Bugs" series)  I'd like to describe several bugs reported by MySQL Community users and fixed in MySQL 5.7.23. As usual, I'll try to concentrate mostly on InnoDB, replication, partitioning and optimizer-related bugs (if any).

Checking MySQL release notes is like swimming with dolphins - it's pure fun
I'd like to start with InnoDB and partitioning-related fixes:
  • The most important fix (that will make downgrades from 5.7.23 more problematic probably) is for Bug #86926 - "The field table_name (varchar(64)) from mysql.innodb_table_stats can overflow.", reported by Jean-François Gagné a year ago. The length of the table_name column in mysql.innodb_table_stats and mysql.innodb_index_stats tables has been increased from 64 to 199 characters (not 100% sure where this new value comes from), and one has to run mysql_upgrade while upgrading to 5.7.23.
  • Bug #90296 - "Hard error should be report when fsync() return EIO". Now this recent request from Allen Lai is implemented.
  • Bug #88739 - "Mysql scalability improvement patch: Optimized away excessive condition". The patch that removes unnecessary check for read-only transactions was suggested by Sandeep Sethia.
  • Bug #86370 - "crash on startup, divide by zero, with inappropriate buffer pool configuration". This funny bug was reported by Shane Bester. I wonder how many more bombs of this kind (use of uint or ulint data types) still remain in the code...
  • Bug #87253 - "innodb partition table has unexpected row lock". This bug was reported by  Yx Jiang and a patch was later suggested by Zhenghu Wen. If the comment at the end is correct, the fix is NOT included in MySQL 8.0.12.
Now let's check some replication bugs fixed:

  • Bug #89272 - "Binlog and Engine become inconsistent when binlog cache file gets out of space". This bug was reported by Yoshinori Matsunobu. Good question in the last comment there, by Artem Danilov:
    "I wonder why does only ENOSPC end up with flush errors and clears the binary log cached. What about any other disk error? Can this fix be extended for all disk errors?"
  • Bug #88891 - "Filtered replication leaves GTID holes with create database if not exists". This serious bug was reported by Simon Mudd
  • Bug #89938 - "Rejoin old primary node may duplicate key when recovery", was reported by Zhenghu Wen, who cares about group replication a lot (unlike me, I have Galera for that).
  • Yes another bug report from Jean-François Gagné, this time in group replication - Bug #89146 - "Binlog name and Pos are wrong in group_replication_applier channel's error msgs".
  • Bug #81500 - "dead branch in search_key_in_table()". This bug was reported 2 years ago by Andrei Elkin, now my colleague (again) in MariaDB. Index is properly used on slave to find rows after this fix.
Surely in MySQL 5.7.23 there had to be some community bug fixed that is kept private. This time it's a bug in mysqldump:
"mysqldump exited abnormally for large --where option values. (Bug #26171967, Bug #86496, Bug #27510150)"
and this is a complete nonsense to me!

The last but not the least, we all should be thankful to Daniël van Eeden for these bug reports and patches contributed:
  • Bug #89001 - "MySQL aborts without proper error message on startup if grant tables are corrupt".
  • Bug #89578 - "Contribution: Use native host check from OpenSSL"
Had you noted any fixes to numerous public bug reports for InnoDB FULLTEXT indexes, "online" DDL or InnoDB compression, or optimizer maybe? I had not, and no wonder - the way these features are used by Community is obviously not something Oracle cares much about.

Anyway, I'd suggest to consider upgrade to MySQL 5.7.23 to anyone who cares about security and uses OpenSSL, replication of any kind or InnoDB partitioned tables in production.


  1. About Bug#86926, I think the 199 value comes from 64 + 3 + 64 + 4 + 64 = 199. The maximum length of a table is 64, table can be partitioned and sub-partitioned, and the naming if sub-partitioned tables is "_table_name_#P#_partition_name_#SP#_sub-partition_name_", which lead to 199 (64 + 3 + 64 + 4 + 64).

  2. "Checking MySQL release notes is like swimming with dolphins - it's pure fun"