Saturday, August 31, 2019

Fun with Bugs #89 - On MySQL Bug Reports I am Subscribed to, Part XXIII

I have to celebrate the anniversary of my last day in Oracle (that was 7 years ago!) somehow, and I think writing yet another blog post about Oracle MySQL bugs is a good way to do this. I am actually surprised (and happy) that public bugs database is still alive, maintained and considered important in Oracle, and I know who in Oracle was working hard all these years for this to happen!

In my previous post in this series I've stopped on Bug #95954 and had not completed review of interesting MySQL bug reports that I've subscribed to in June 2019. So, below I start with the next bug in my list, complete review for June and cover some bugs reported in July. There were many.
  • Bug #95957 - "IN operator issue when comparing signed column and the column cast to unsigned". This bug was reported by Manuel Rigger. As far as I can see, MariaDB 10.3 is not affected:
    MariaDB [test]> CREATE TABLE t0(c0 INT);
    Query OK, 0 rows affected (0.518 sec)

    MariaDB [test]> INSERT INTO t0(c0) VALUES(-1);
    Query OK, 1 row affected (0.196 sec)

    MariaDB [test]> SELECT t0.c0 IN (1, CAST(t0.c0 AS UNSIGNED)) from t0;
    +---------------------------------------+
    | t0.c0 IN (1, CAST(t0.c0 AS UNSIGNED)) |
    +---------------------------------------+
    |                                     0 |
    +---------------------------------------+
    1 row in set, 1 warning (0.207 sec)

    MariaDB [test]> show warnings\G
    *************************** 1. row ***************************
      Level: Note
       Code: 1105
    Message: Cast to unsigned converted negative integer to it's positive complement

    1 row in set (0.013 sec)
  • Bug #96001 - "No warning when creating foreign key in MyISAM tables". I am really surprised that this "documented feature" was accepted as a S3 bug when reported by Przemyslaw Malkowski from Percona. But this happened. I also prefer NOT to have unsupported syntax just ignored silently and would like to see a warning (or error in strict mode).
  • Bug #96002 - "'variable log_bin_trust_function_creators' -variable is "hidden"." Consistency is important, as well as correct documentation. So I was happy to see this bug report from Peter Laursen. 75(!) of his bug reports are still active, by the way, some were reported more than 10 years ago. I wonder if anyone is going to check (if not fix) them any time soon.
  • Bug #96079 - "large_tests.innodb_innochecksum_3gb test failing with debug build." Yet another MTR test failure reported by Lalit Choudhary from Percona.
  • Bug #96100 - "Generated column cause a heap-use-after-free error". Probably ASan builds are not tested as carefully in Oracle as they are by some community members, like Zkong Kong who reported this bug. Otherwise they would mark this bug report as a duplicate of some known internal bug.
  • Bug #96108 - "To run mtr "innodb.log_flush_order" MySql Server would be always core down". I've listed the bug as an example that even though code modification is needed to reproduce the crash (reported by Juncai Meng) literally, it was accepted and "Verified". In other reports this sometimes not happen, and the point is that it is surely not a rule carved in stone in Oracle to NOT accept bugs if test case involves code modification. Remember that and fight for your reports if needed.
  • Bug #96128 - "Doc: documentation is inaccurate when InnoDB starts with innodb_read_only". Correct manual matters a lot, so nice to have it corrected in this case by Calvin Sun.
  • Bug #96134 - "Please provide control functions for the IO Thread." I'd be also happy to see a way to control replication I/O thread progress and read logs only up to some position or GTID, per channel. Thanks Jean-François Gagné for this nice feature request.
  • Bug #96142 - "Inconsistent error on slave for Update event on table with non-exists partition". Yet another by report from by Lalit Choudhary. Good to see multiple versions check.
  • Bug #96148 - "using Invisible Index when slave apply EVENT". This bug was reported by Songlei Wang. Consistency matters, so if the index is invisible it should remain invisible for replication SQL thread as well. See also his another Bug #96150 - "'show slave status' show the Inaccurate Last_IO_Error message".
  • Bug #96167 - "Many header files now missing from devel package". As noted by Manuel Ung, now it is impossible to build plugins and UDFs unless users download the source tree, and then copy the headers to the appropriate places. Packaging in hard.
  • Bug #96178 - "mysqldump leaks memory when selected tables are dumped with --order-by-primary". Abhinav Sharma proposed a simple MTR test case to run on ASan build, and suggested a fix. Very nice bug report. Unfortunately I do not see any statements about the results of checking MySQL 8.0.x.
  • Bug #96192 - "Possible race condition with binlog-transaction-dependency-tracking". Bug reporter, Herman Lee, complained about one place in the code where race condition may happen even after the fix for one MySQL bug. Does it really matter for bug verification if he found more places? I fail to see a reason to keep he bug in "Need Feedback" status, when code review is enough to confirm there is a problem in that one part of the code clearly identified.
  • Bug #96196 - "performance_schema_accounts_size and p_s_hosts_size limited by 16384", Nice bug that can be confirmed by code review or just opening many connections was reported by Nikolai Ikhalainen from Percona. Autoscaling is broken/limited in this case.
  • Bug #96340 - "Slow startup for mysql 8.0 with many tables due to the tablespace files scan". This is actually a regression comparing to 5.7, but it's visible on slow disks. It's nice to see useful discussion, explanations and patch suggested (by Sunny Bains) in this bug report created by Lalit Choudhary.
I started this summer in a beautiful Barcelona. This blog posts ends it for me. One of the good changes leaving Oracle seven years ago introduced in my life is a real freedom to work from anywhere and travel as often as I really want, both for work and for fun.
To summarize:
  1. I am happy to see MySQL public bugs database still up and widely used, even though I do not work on it directly for 7 years already. It's a key service and media for cooperation for the entire MySQL Community! Just check how it happens in Bug #96340.
  2. Consistency matters.
  3. I still see cases when the time is wasted at bugs verification stage.
  4. MySQL fine manual still have details explained incorrectly, and this is unfortunate.
  5. Sometime I wonder why Percona engineers and other MySQL Community users manage to find even MTR test failures faster than anyone in Oracle cares to report and fix them. They all know magic (like actually running all tests on debug builds and checking the results, maybe). Or, maybe, they care?
* * *
Shameless self-promotion at the end. First time since 2015 I am going to attend Percona Live conference and speak there. Ticket prices increase on September 1, so using code CMESPEAK-VALERII you’ll get the best deal right now.

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