Saturday, August 10, 2019

Fun with Bugs #88 - On MySQL Bug Reports I am Subscribed to, Part XXII

It's Saturday night. I have a week of vacation ahead that I am going to spend at home, working on things I usually do not have time for. I already did something useful (created a couple of test cases for MariaDB bugs here and there, among other things), so why not to get some fun and continue my previous review of recent interesting MySQL bug report...

So, here is the list of 15 more MySQL community bug reports that I've subscribed to back in May and June 2019:
  • Bug #95491 - "The unused wake up in simulator AIO of function reserve_slot". I am impressed by the fact that these days many people just study InnoDB code, find problematic parts, improve them, test and prove the improvement, and submit patches to Oracle. Chen Zongzhi, who reported this bug, is one of such great people.
  • Bug #95496 - "Replication of memory tables". As pointed out by Iwo P, MySQL manual describes what happens to MEMORY tables replicated from master to slave in details, including the case of master restart. But one detail is missing - when slave with MEMORY tables restarts, even with super_read_only set, it also generates even to delete data from the table into its own binary log, with GTID, and this leads to problems in case of failover.
  • Bug #95507 - "innodb_stats_method is not honored when innodb_stats_persistent=ON". This bug was reported by my colleague Sergei Petrunia. See also related MDEV-19574  (still "Open").
  • Bug #95547 - "MySQL restarts automatically after ABORT_SERVER due to disk full". I am not sure this is a replication bug, more a problem of too primitive mysqld_safe or systemd startup scripts that do not check free space on disk or reason why mysqld process committed suicide. Anyway, this report by Przemyslaw Malkowski from Percona was accepted as a replication bug.
  • Bug #95582 - "DDL using bulk load is very slow under long flush_list". As found and proved by Fungo Wang, due to optimized away redo log writing for bulk load, to make sure such DDL is crash safe, dirtied pages must be flushed to disk synchronously. Currently this is done inefficiently, as shown in this bug report. See also a year old (and still "Open") Bug #92099 - "provide an option to record redo log for bulk loading" from the same reporter, where he asks for a way to get redo logging back (but still benefit from other "online" ALTER features). MariaDB has that option after the fix of MDEV-16809.
  • Bug #95612 - "replication breakage due to Can not lock user management caches for processing". Simon Mudd noted that in some cases simple DROP USER IF EXISTS ... breaks parallel replication in MySQL 8.0.16. Good to know that START SLAVE allows to continue :)
  • Bug #95698 - "JSON columns are returned with binary charset". This bug was reported by Daniel Book. Note that according to the original issue, DBD::MariaDB (I had no idea this exists!) works properly with MariaDB 10.3 or 10.4. I had not checked.
  • Bug #95734 - "Failing SET statement in a stored procedure changes variables". This really weird and unexpected bug was reported by Przemysław Skibiński.
  • Bug #95863 - "MTS ordered commit may cause deadlock ". Great finding by Lalit Choudhary from Percona!
  • Bug #95895 - "Shutdown takes long time when table uses AUTOINC and FOREIGN KEY constraints". It was reported by Satya Bodapati from Percona, who later contributed as patch. See also his related Bug #95898 - "InnoDB releases memory of table only on shutdown if table has FK constraint". I truly hope to see these fixed in next minor releases of MySQL. Note that originally bug (PS-5639) was reported by Sveta Smirnova.
  • Bug #95928 - "InnoDB crashes on compressed and encrypted table when changing FS block size". Make sure to check and write original filesystem block size somewhere... This bug was reported by Sergei Glushchenko from Percona.
  • Bug #95929 - "Duplicate entry for key 'PRIMARY' when querying information_schema.TABLES". This nice feature of new data dictionary of MySQL 8.0.16 under concurrent load was found by Manuel Rigger.
  • Bug #95934 - "innodb_flush_log_at_trx_commit = 0 get performance regression on 8 core machine". If I had access to 8 cores box, I'd try to check this sysbench-based complete test case immediately. I should do this on my quadcore box at least, next week. But here we see some 12 days just wasted and then bug report from Chen Zongzh ended up "Analyzing", till today, with no further feedback.
  • Bug #95954 - "CAST of negative function return value to UNSIGNED malfunctions with BIGINT". Yet another weird bug found by Manuel Rigger. There are patches (separate for 5.6, 5.7 and 8.0) contributed by Oleksandr Peresypkin.
Montjuïc is a place to enjoy nice view of Barcelona and forget about MySQL bugs. So, I could miss some interesting ones at the end of May, 2019...
To summarize:
  1. Percona engineers still contribute a lot of useful and interesting MySQL bug reports, often - with patches.
  2. I am impressed by quality of MySQL bug reports in 2019. Often we see detailed analysis, proper complete test cases and patches.
  3. There is a recent fork of DBD::mysql for MariaDB (and MySQL), DBD::MariaDB!
  4. I badly need some new hardware for running benchmarks and tests from recent bug reports...
  5. I should spend more time in May in Barcelona :)

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