Fun with Bugs #59 - On MySQL Bug Reports I am Subscribed to, Part II

New Year (that starts on Monday!) gives a good opportunity to change something in our lives, start doing something new, better or different. Let's assume I failed with all these so far, as I am again posting about MySQL bugs here.

Since my previous post on this topic I've subscribed to 15 more MySQL bugs, and being on a combination of public holidays and vacation now gives me a good opportunity to review these bug reports.

Here they are, starting from the most recent:

• Bug #89065 - "sync_binlog=1 on a busy server and slow binary log filesystem stalls slaves". I do not remember seeing multiple threads in "Finished reading one binlog; switching to next binlog" state, but it would be interesting to see this bug report processed properly.
• Bug #89051 - "EXPLAIN output is different for same content depending when index was added". The way optimizer decides on "range" vs "ref" access is always interesting. Here, based on a recent comment by Øystein Grøvlen, the bug is actually that "Cost values are not correct when optimizer switch from ref-access to range-access in order to use more key parts".
• Bug #88914 - "Potential null pointer dereference at pointer node->undo_recs (row0purge.cc)". It's funny to see many bugs becoming private as "security" ones and, at the same time, this bug, where reporter suspects it is exploitable, being "Open" and ignored for more than two weeks...
• Bug #88891 - "Filtered replication leaves GTID holes with create database if not exists". I can not even explain how much I "like" all kinds of GTIDs I have to deal with, especially such a long lists of GTIDs that may be created in cases described in this report.
• Bug #88863 - "COUNT(*) can sometimes return bogus value". Now, this is a really funny bug! It must be some race condition, and I'd really prefer to see this bug fixed soon.
• Bug #88844 - "MySQL crash with InnoDB assertion failure in file pars0pars.cc". Nice crash (that I've never seen before) quickly reproduced by Shane Bester.
• Bug #88834 - "Uneven slowdown on systems with many users". What can be better to speed up connection than checking the list of users one by one, especially when there are thousands of users?
• Bug #88827 - "innodb uses too much space in the PK for concurrent inserts into the same table". As Mark Callaghan put it:
  

  "I am not sure my reproduction details will ever satisfy Sinisa but I don't mind if you don't fix this because I care more about MyRocks today and this bug makes MyRocks look better."

  We (Facebook's MySQL, MariaDB and Percona server users) do have MyRocks, but why poor Oracle MySQL users should suffer? Let's hope Sinisa Milivojevic will process the bug fast, with all the details clarified there :)
• Bug #88791 - "Binary log for generated column contains new value as WHERE clause, not old value". Generated columns and binary logging, what could went wrong?
• Bug #88764 - ""ALTER TABLE MODIFY..." takes time even if leaving table as is". Any simple test cases they come to my mind do NOT let to reproduce this problem, but I feel some potential as soon as more exotic cases like partitioning or data directory settings are considered. Let's wait for bug reporter to clarify.
• Bug #88720 - "Inconsistent and unsafe FLUSH behavior in terms of replication". Nice summary of problems from Przemyslaw Malkowski. One more reason for me to hate GTIDs, honestly.
• Bug #88694 - "MySQL accepts wildcard for database name for table level grant but won't use it". One more problem with privileges reported by Daniël van Eeden.
• Bug #88674  - "Regression CREATE TBL from 5.7.17 to 20 (part #2: innodb_file_per_table = OFF)." and Bug #88673 - "Regression CREATE TBL from 5.7.17 to 20 (part #1: innodb_file_per_table = ON)." - these two bugs were reported by Jean-François Gagné and clearly show some things that are done wrong by Oracle when fixing (private, "security") bugs...
• Bug #88671 - "ALL + BNL chosen over REF in query plan with a simple SELECT + JOIN". In this case optimizer (probably) does not take costs into account properly when choosing block nested loop join vs usual "ref" index access. Maybe just a matter of missing/wrong statistics also. It would be interesting to find out eventually.
• Bug #88666 - "I_S FILES : all rows are displayed whatever the user privileges". Yet another bug report from Jocelyn Fournier. I am actually surprised with a number of bugs related to privileges that I notice recently.
• Bug #88633 - "Auto_increment value on a table is less than max(id) can happen". It seems only MySQL 5.7.x is affected, but not 5.6.x.
• Bug #88623 - "Modifying virtually generated column is not online". May be by design, but still surprising.
• Bug #88534 - "XA may lost prepared transaction and cause different between master and slave". XA transactions with MySQL is still a sure way to disaster, I think. See Bug #87526 also that should appear in the next part of this series...

Stay tuned to more posts about MySQL bugs from me in the New Year of 2018!