I've subscribed to more than 60 new bug reports since my previous post in this series. It means that
I'd need 4-5 posts to cover all new subscriptions and reasons
behind them. I still plan to write about most of the bug reports
I was interested in recently, but for this post I decided to pick
up only MySQL 8.0 regression bugs and pay special attention to
those that could be handled better or faster by Oracle engineers,
as well as those handled perfectly.
The initial reason for this special attention originally
was Bug #93085 - "Stall when concurrently
execute create/alter user with flush privilege", that caused
a lot of interesting Twitter …
Nov
18
2018
Sep
26
2018
A query plan uses loose index scan if “Using index for group-by” appears in the “Extra” column of the EXPLAIN output. In some plans though, “Using index for group-by (scanning)” appears. What does “(scanning)” mean and how is it different from the regular loose index scan?…
Sep
25
2018
Lately, I worked on several queries which started returning wrong results after upgrading MySQL Server to version 5.7 The reason for the failure was derived merge optimization which is one of the default
optimizer_switch
options. Issues were solved, though at the price of performance, when we turned it
OFF
. But, more importantly, we could not predict if any other query would start returning incorrect data, to allow us to fix the application before it was too late. Therefore I tried to find reasons why
derived_merge
can fail. Analyzing the problem
In the first run, we turned SQL Mode
ONLY_FULL_GROUP_BY
on, and this removed most of the problematic queries. That said, few of the queries that were successfully working with
ONLY_FULL_GROUP_BY
were affected.
A quick search in the …
[Read more]
Aug
04
2018
More than 2 months passed since my previous review of active MySQL bug reports I
am subscribed to, so it's time to describe what I was interested
in this summer.
Let's start with few bug reports that really surprised me:
- Bug #91893 - "LOAD DATA INFILE throws error with NOT NULL column defined via SET". The bug was reported yesterday and seem to be about a regression in MySQL 8.0.12 vs older versions. At least I have no problem to use such a way to generate columns for LOAD DATA with MariaDB 10.3.7.
- Bug #91847 - "Assertion `thread_ids.empty()' failed.". As usual, Roel Van de Paar …
May
28
2018
Last time I reviewed my recent subscriptions
to MySQL bugs it was April 1, 2018. I was busy working, blogging
about other bugs, running random MTR tests on MySQL 8.0.11 and
got two weeks of vacation since than. Now it's time to briefly
review 20 recent bug reports (mostly for MySQL 8.0.11) I was
interested in.
As usual, I start with most recent bug reports:
- Bug #91010 - "WolfSSL build broken due to cmake typo". MySQL 8 can be compiled using wolfSSL according to the manual, but as Laurynas Biveinis found this is not the case in practice, and not only because of the typo in libutils.cmake. It seems …
Apr
15
2018
I have some free time today, but I am still lazy enough to work
on numerous planned and pending "ToDo" kind of posts, so why not
to continue review of older MySQL bugs I am
subscribed to. Today I am going to list 15 more bugs reported
more than a year ago and still not fixed:
- Bug #85805 - "Incorrect ER_BAD_NULL_ERROR after LOAD DATA LOCAL INFILE". This detailed bug report by Tsubasa Tanaka stays "Verified" for more than a year already. It's a great example of gdb use for MySQL troubleshooting. Setting a couple of breakpoints may really help to understand how MySQL works and why some …
Apr
01
2018
I've subscribed to more than 15 new MySQL bug reports since
the previous post in this series, so it's time
for a new one. I am trying to follow important, funny or hard to
process bug reports every day. Here is the list of the most
interesting recent ones starting from the latest (with several
still not processed properly):
- Bug #90211 - "Various warnings and errors when compiling MySQL 8 with Clang". Roel Van de Paar and Percona in general continue their QA efforts in a hope to make MySQL 8 better. Current opinion of Oracle …
Mar
27
2018
In this post, I’ll discuss the fix for lp:1704195 (migrated to PS-2503), which prevents
ANALYZE TABLE
from blocking all subsequent queries on the same table.
In November 2017, Percona released a fix for lp:1704195 (migrated to PS-2503), created by Laurynas Biveinis. The fix, included with Percona Server for MySQL since versions 5.6.38-83.0 and 5.7.20-18, stops
ANALYZE TABLE …[Read more]
Feb
11
2018
Since my previous post on this topic I've subscribed to
19 more MySQL bugs, so it's time for yet another review of these
reports. I am trying to pick up important, funny or hard to
process reports every day, and here is the list of the most
interesting ones starting from the latest:
- Bug #89607 - "MySQL crash in debug, PFS thread not handling singals." We have a patch contributed by Robert Golebiowski.
-
Bug #89583 - "no rpm build instructions
from source git tree". As Simon Mudd put it:
"... The sources are supposed to be in the git tree …
Jan
16
2018
Oracle had formally released MySQL 5.7.21 yesterday. I do not
bother any more to study MySQL release notes carefully and
completely, but during a quick review today I've noted several
interesting items I'd like you to pay attention to.
I am historically interested in InnoDB implementation details, so
I could not miss Bug
#87619 - "InnoDB partition table will lock into the near
record as a condition in the use ". This was a regression bug
in 5.7+, probably caused by new implementation of partitioning in
InnoDB.
Another interesting bug is Bug
#86927 - "Renaming a partitioned table does not update
mysql.innodb_table_stats.", by …