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As promised, I am trying to write one blog post in this series per week. So, even though writing about InnoDB row formats took a lot of time and efforts this weekend, I still plan to summarize my findings, questions, discussions, bugs and links I've collected over this week.
I've shared two links this week on Facebook that got a lot of comments (unlike links to my typical blog posts). The first one was to Marko Mäkelä's blog post at MariaDB.com, "InnoDB Quality Improvements in MariaDB Server". I do not see any comments (or any obvious way to comment) there, but the comments I've got at Facebook were mostly related to the statement that
"We are no longer merging new MySQL features with MariaDB..."
noted in the text by Mark Callaghan and to the idea that "InnoDB" is a trademark of Oracle, so using it to refer to a fork (that is incompatible with the "upstream" InnoDB in too many ways since MariaDB 10.1 probably) is wrong, as stated by Matt Lord and Sunny Bains. People in the comments mostly agree that a new name makes sense (there are more reasons to give it now anyway than in the case of XtraDB by Percona), and we had a lot of nice and funny suggestions on Slack internally (FudDB was not among them, this is a registered trademark of Miguel Angel Nieto for many years already). We shell see how this may end up, but I would not be surprised by a new name announced soon. I suggest you to read comments in any case if you have a Facebook account, many of them are interesting.
The second link was to Kaj Arnö's post at mariadb.org, "On Contributions, Pride and Cockiness". It's worth checking just because of Monty's photo there. Laurynas Biveinis stated in the comments that any comparison of number of pull requests (open and processed) is meaningless when development model used by other parties is different (closed, with contributions coming mostly via bug reports in case of Oracle, or all changes, external and internal, coming via pull requests in case of Percona). MariaDB uses a mix of a kind, where some contributions from contractors come via pull requests, while engineers from MariaDB Corporation work on GitHub sources of MariaDB Server directly. Anyway (meaningless statistics aside), MariaDB seems to be the easiest target for contributions from Community at the moment, and nobody argued against that. My followers also agreed that the same workflow for internal and external contributions is a preferred development model in ideal world.
This kind of public discussions of (serious and funny) MySQL-related matters on Facebook (along with public discussions on MySQL bugs) make me think the way I use my Facebook page is proper and good for the mankind.
Now back to notes made while working on Support issues. This week I had to explain one case when MariaDB server was shut down normally (but unexpectedly for DBA):
2019-05-22 10:37:55 0 [Note] /usr/libexec/mysqld (initiated by: unknown): Normal shutdown
This week I've spent a lot of time and some efforts trying to reproduce the error (1942 and/or 1940 if anyone cares) on Galera node acting as an async replication slave. These efforts ended up with a bug report, MDEV-19572. Surely the idea to replicate MyISAM tables outside of mysql database to Galera cluster is bad at multiple levels, but why the error after running for a long time normally? In the process of testing I was reading various remotely related posts, so checked this and that... I also hit other problems in the process. Like this crash that happened probably while sending some signal to the node unintentionally:
190523 17:19:46 [ERROR] mysqld got signal 11 ; This could be because you hit a bug. It is also possible that this binary or one of the libraries it was linked against is corrupt, improperly built, or misconfigured. This error can also be caused by malfunctioning hardware.
To report this bug, see https://mariadb.com/kb/en/reporting-bugs
We will try our best to scrape up some info that will hopefully help diagnose the problem, but since we have already crashed, something is definitely wrong and this may fail.
Server version: 10.2.23-MariaDB-log key_buffer_size=134217728 read_buffer_size=131072 max_used_connections=3 max_threads=153 thread_count=65544 It is possible that mysqld could use up to key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 467240 K bytes of memory Hope that's ok; if not, decrease some variables in the equation.
Thread pointer: 0x0 Attempting backtrace. You can use the following information to find out where mysqld died. If you see no messages after this, something went terribly wrong... stack_bottom = 0x0 thread_stack 0x49000 /home/openxs/dbs/maria10.2/bin/mysqld(my_print_stacktrace+0x29)[0x7f6475eb5b49] /home/openxs/dbs/maria10.2/bin/mysqld(handle_fatal_signal+0x33d)[0x7f64759d50fd] /lib/x86_64-linux-gnu/libpthread.so.0(+0x10330)[0x7f6473887330] /home/openxs/dbs/maria10.2/bin/mysqld(+0xb3b817)[0x7f6475ebc817] /home/openxs/dbs/maria10.2/bin/mysqld(+0xb3b9e6)[0x7f6475ebc9e6] /home/openxs/dbs/maria10.2/bin/mysqld(+0xb3bb8a)[0x7f6475ebcb8a] /home/openxs/dbs/maria10.2/bin/mysqld(lf_hash_delete+0x61)[0x7f6475ebcfa1] /home/openxs/dbs/maria10.2/bin/mysqld(+0x601eed)[0x7f6475982eed] include/my_atomic.h:298(my_atomic_storeptr)[0x7f6475983464] sql/table_cache.cc:534(tdc_delete_share_from_hash)[0x7f6475811f17] sql/table_cache.cc:708(tdc_purge(bool))[0x7f64759351ea] sql/sql_base.cc:376(close_cached_tables(THD*, TABLE_LIST*, bool, unsigned long))[0x7f64757c9ec7] nptl/pthread_create.c:312(start_thread)[0x7f647387f184] /lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7f6472d8c03d] The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains information that should help you find out what is causing the crash.
I was not able so far top find the exact some backtrace in any known MariaDB bug, so one day I'll have to try to reproduce this crash as well.
I try to check some MariaDB ColumnStore issues from time ot time, for a change, and this week I ended up reading this KB page while trying to understand how much we can control placement of data there.
Finally, for the records, this is the way to "fix" InnoDB statistics if needed (and the need is real as you can find out from Bug #95507 - "innodb_stats_method is not honored when innodb_stats_persistent=ON" reported by my colleague Sergei Petrunia):
update mysql.innodb_index_stats set last_update=now(), stat_value=445000000 where database_name='test' and table_name='t1' and index_name='i1' and stat_name='n_diff_pfx01';
I like to return to familiar nice places and topics, like Regent's Canal or MySQL bugs...
The last bug not the least, MySQL bugs. This week I've subscribed to the following (already "Verified") interesting bug reports (besides the one mentioned above):
Bug #95484 - "EXCHANGE PARTITION works wrong/weird with different ROW_FORMAT.". Jean-François Gagné found out that there is a way to have partitions with different row_format values in the same InnoDB table, at least in MySQL 5.7. So why is this not supported officially? See also his Bug #95478 - "CREATE TABLE LIKE does not honour ROW_FORMAT.". It's a week of ROW_FORMAT studies for me, for sure!
Bug #95462 - "Data comparison broke in MySQL 8.0.16". It's common knowledge how much I like regression bugs. MySQL 8.0.16 introduced a new one, reported by Raman Haran, probably based on some good and valid intentions. But undocumented changes in behavior in GA versions are hardly acceptable, no matter what are the intentions.
That's all for now. Some more links to MySQL bugs from me are always available on Twitter.
Let me start with a short summary and then proceed with a long story, code snippets, hexdumps, links and awk functions converted from the source code of MariaDB server. This blog post can be summarized as follows:
One can find row_format used to create table explicitly in the .frm file (or the outputs of SHOW CREATE TABLE or SHOW TABLE STATUS). Internals manual may help to find out where is it stored and source code reading helps to find the way to interpret the values.
For InnoDB tables created without specifying the row_format explicitly neither logical backup nor .frm file itself contains the information about the row format used. There are 4 of them (Redundant, Compact, Dynamic and Compressed). The one used implicitly is defined by current value of the innodb_default_row_format that may change dynamically.
At the .ibd file level there is no (easy) way to distinguish Redundant from Compact, this detail should come from elsewhere. If the source table's row format had NOT changed you can find it from the information_schema.innodb_sys_tables (or innodb_tables in case of MySQL 8), or from the output of SHOW TABL STATUS.
There is an easy enough way to check tablespace level flags in the .ibd file (sample awk functions/script are presented below) and this helps to find out that the row format was Compressed or Dynamic.
So far in basic cases (encryption etc aside) individual .ibd files for InnoDB tables from MariaDB (even 10.3.x) and MySQL 8.0.x are compatible enough.
You have to take all the above into account while importing individual tables to do partial restore or copy/move tablespaces from one database to the other.
Some useful additional reading and links may be found in MariaDB bug reports MDEV-19523 and MDEV-15049. Yes, reading MariaDB MDEVs may help MySQL DBAs to understand some things better!
Now the real story.
I miss London, so I am going to be there on June 13 to partcipate in Open Databases Meetup. Should I speak about importing InnoDB tablespaces there?
* * *
This is a long enough blog post about a "research" I had to make while working in Support recently. It all started with a question like this in a support issue earlier in May:
"Is it somehow possible to extract ROW_FORMAT used from a table in a backup in XtraBackup format?"
The context was importing tablespace for InnoDB table and error 1808, "Schema mismatch", and customer had a hope to find out proper format without attempts to import, in some way that can be scripted easily. When one tries to import .ibd file with a format that does not match .frm file or data dictionary content, she gets a very clear message in MariaDB (that still presents all thee details) due to the fix in MDEV-16851, but the idea was to avoid trial and error path entirely.
There were several ideas on how to proceed. Given the .frm, one could use mysqlfrm utility (you can still find MySQL Utilities that are only under Sustaining Support by Oracle here) to get full CREATE TABLE from the .frm. But I was sure that just checking ROW_FORMAT should be easier than that. (Later test of latest mysqlfrm I could get running on Fedora 29 proved that it was a good idea to avoid it due to some problems I may write about one day.) Fine MySQL Internals Manual clearly describes .frm file format and shows that at offset 0x28 in the header section we have row_type encoded as one byte:
Quick search in source code ended up with the following defined in sql/handler.h (links refer to MariaDB code, but the idea is clear and same for MySQL as well):
The rest looked clear at the moment. We should see decimal values from 2 to 5 at offset 0x28 (decimal 40) from the beginning of the .frm file representing row formats supported by InnoDB. I quickly created a set of tables with different row formats:
But in real customer case there was no problem with tables created with explicit row_format set (assuming the correct .frm was in place). The problem was with table like ti5 above, those created with the default row format:
MariaDB [test]> show variables like 'innodb%format'; +---------------------------+---------+ | Variable_name | Value | +---------------------------+---------+ | innodb_default_row_format | dynamic | | innodb_file_format | | +---------------------------+---------+ 2 rows in set (0.001 sec)
In .frm file (and in SHOW CREATE TABLE output) the format is NOT set, it's default, 0 (or 0x00 in hex). The problem happens when we try to import such a table into an instance with different innodb_default_row_format. Consider the following test case:
[openxs@fc29 maria10.3]$ bin/mysql --socket=/tmp/mariadb.sock -uroot test Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A
Welcome to the MariaDB monitor. Commands end with ; or \g. Your MariaDB connection id is 9 Server version: 10.3.15-MariaDB Source distribution
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
In this test we create a new table, ti0, in other database, test2, that has ROW_TYPE_DEFAULT (0) in the .frm file, same as the test.ti5 table created above. But if we try to import t5 tablespace by first exporting it properly in another session:
MariaDB [test2]> \! cp data/test/ti5.cfg data/test2/ti0.cfg MariaDB [test2]> \! cp data/test/ti5.ibd data/test2/ti0.ibd MariaDB [test2]> alter table ti0 import tablespace; ERROR 1808 (HY000): Schema mismatch (Table flags don't match, server table has 0x1 and the meta-data file has 0x21; .cfg file uses ROW_FORMAT=DYNAMIC)
we fail with error 1808 (that has all the details about the original's table row format, DYNAMIC, and hex information about some flags in hex that are different). We failed because now innodb_default_row_format is different, it's COMPACT!
We can not fool the target server by removing (or not copying) non-mandatory .cfg file:
Now we see a bit different text, but the same error 1808. Real row format of InnoDB table is stored somewhere in .ibd file. As you can guess, copying .frm file (as it may when we copy back files from Xtrabackup- or mariabackup-based backup to do partial restore) also does not help - the files had the same row_format anyway and we verified that. So, real row format of InnoDB table is stored somewhere in InnoDB (data dictionary). When it does not match the one we see in .ibd file we get error 1808.
How to resolve this error? There are two ideas to explore (assuming we found the real format in .ibd file somehow):
Try to create target table with proper row_format and then import.
Set innodb_default_row_format properly and create target table without explicit row format set, and then import.
The first one works, as one can find out (but will end up with different .frm file than the original table had, surely). Check these:
MariaDB [test2]> select * from test.ti5; +----+------+ | id | c1 | +----+------+ | 5 | 5 | +----+------+ 1 row in set (0,001 sec)
MariaDB [test2]> \! cp data/test/ti5.ibd data/test2/ti0.ibd MariaDB [test2]> alter table ti0 import tablespace; ERROR 1808 (HY000): Schema mismatch (Expected FSP_SPACE_FLAGS=0x0, .ibd file contains 0x21.) MariaDB [test2]> \! cp data/test/ti5.cfg data/test2/ti0.cfg MariaDB [test2]> alter table ti0 import tablespace; ERROR 1808 (HY000): Schema mismatch (Table flags don't match, server table has 0x1 and the meta-data file has 0x21; .cfg file uses ROW_FORMAT=DYNAMIC) MariaDB [test2]> drop table ti0; Query OK, 0 rows affected (0,168 sec)
So, if you care to understand the flags (we'll work on that below) or care to copy .cfg file as well, you surely can get the row format of the table. Now let's re-create ti0 with explicitly defined Dynamic row format and try to import again:
MariaDB [test2]> show warnings\G *************************** 1. row *************************** Level: Warning Code: 1810 Message: IO Read error: (2, No such file or directory) Error opening './test2/ti0.cfg', will attempt to import without schema verification 1 row in set (0,000 sec)
MariaDB [test2]> select * from ti0; +----+------+ | id | c1 | +----+------+ | 5 | 5 | +----+------+ 1 row in set (0,001 sec)
We see that copying .cfg file is not really mandatory and that explicit setting of ROW_FORMAT (assuming that .frm file is NOT copied) works.
The second idea also surely works (and customer in his trial and error attempts just tried with all possible formats until import was successful). Lucky from the first error we'll know the original format used for sure:
MariaDB [test2]> select * from ti0; +----+------+ | id | c1 | +----+------+ | 5 | 5 | +----+------+ 1 row in set (0.000 sec)
MariaDB [test2]> show create table ti0\G *************************** 1. row *************************** Table: ti0 Create Table: CREATE TABLE `ti0` ( `id` int(11) NOT NULL, `c1` int(11) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 1 row in set (0.000 sec)
Now we can proceed with UNLOCK TABLES in that another session where we flushed test.ti5 for export.
How could we find out the row format to use without trial and error, now that we know in one specific case .frm file (or even CREATE TABLE statement shown by server or mysqldump) misses it?
First of all we could try to save this information (select @@innodb_default_file_format) alone with the backup. But that would show the value of this variable at the moment of asking, and it could be different when specific table was created. Does not work in general case.
We could use SHOW TABLE STATUS also, as follows:
MariaDB [test]> show create table ti5\G *************************** 1. row *************************** Table: ti5 Create Table: CREATE TABLE `ti5` ( `id` int(11) NOT NULL, `c1` int(11) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 1 row in set (0.001 sec)
MariaDB [test]> show table status like 'ti5'\G *************************** 1. row *************************** Name: ti5 Engine: InnoDB Version: 10 Row_format: Dynamic ...
In the example above that table was created without setting row_format explicitly, but we see the real one used in the output of SHOW TABLE STATUS. So, if we cared enough, this kind of output could be saved when the data were backed up or exported.
Then we could try to get it for each table from the InnoDB data dictionary of the system we get .ibd files from. In older MySQL versions we'd have to dig into the real data dictionary tables on disk probably, but in any recent MySQL (up to 5.7, 8.0 may be somewhat different due to a new data dictionary) or MariaDB we have a convenient, SQL-based way to get this information. There are two INFORMATION_SCHEMA tables to consider: INNODB_SYS_TABLESPACES and INNODB_SYS_TABLES. The first one is not good enough, as it considers Compact and Redundant row formats the same (even though fine MySQL Manual does not say this):
In the table above I was wondering about the exact values in FLAG column (note 33, 0x21 in hex, looks familiar from the error message in previous examples). MySQL Manual says just this:
"A numeric value that represents bit-level information about tablespace format and storage characteristics."
MariaDB's KB page is now way more detailed after my bug report, MDEV-19523, was closed. See the link for the details, or check the code of the i_s_dict_fill_sys_tables() function if you want to interpret the data properly:
/opt/mysql/product/5.7.26/bin/mysqldump --user=dba --host=migzm96i --port=3306 --all-databases --quick --single-transaction --flush-logs --triggers --routines --hex-blob --events | tee >(md5sum --binary >/tmp/checksum.23357.md5) | gzip -1
to Destination: /var/mysql/dumps/mysql96i/daily/bck_mysql96i_full_2019-05-22_06-50-01.sql.gz
ERROR: /opt/mysql/product/5.7.26/bin/mysqldump command failed (rc=253).
mysqldump: [Warning] Using a password on the command line interface can be insecure.
Error: Couldn't read status information for table m_report_builder_cache_157_20190521035354 ()mysqldump: Couldn't execute 'show create table `m_report_builder_cache_157_20190521035354`': Table 'totara.m_report_builder_cache_157_20190521035354' doesn't exist (1146)
There are various strategies to work around this problem:
If the table is only temporary create it with the CREATE command as a TEMPORARY TABLE instead of a normal table. This workaround would not work in this case because the table is a caching table which must be available for other connections as well.
Try to schedule your application job or your bman job in the way they do not collide. With bman that is quite easy but sometimes not with the application.
Try to create the table in its own schema (e.g. cache) which is excluded from bman backup. So you can easily do a bman backup without the cache schema. For example like this:
If this strategy also does not work (because you cannot change the application behaviour) try to ignore the table. The underlying command mysqldump knows the option --ignore-table:
--ignore-table=name Do not dump the specified table. To specify more than one
table to ignore, use the directive multiple times, once
for each table. Each table must be specified with both
database and table names, e.g.,
This option can be used in bman as well. Options to the underlying application are passed through FromDual Backup Manager as follows:
The problem here is, that this table contains a timestamp in its table name (20190521035354). So the table name is changing all the time. To pass through wildcards with --ignore-table is not possible with mysqldump. The tool mysqldump does not support (yet) this feature. The only solution we have in this case is, to ignore the error message with the risk that possible other error messages are also ignored. This is achieved again with the --pass-through option:
My previous post from this series was published more than 1.5 years ago. I had never planned to stop writing about my everyday work on a regular basis, but sometimes it's not easy to pick up something really interesting for wider MySQL audience and when in doubts I always prefer to write about MySQL bugs...
In any case, any long way starts from the first step, so I decided to write one post in this series per week and try to summarize in it whatever findings, questions, discussions, bugs and links I've collected over the week. My work experience differs week after week, so some of these posts may be boring or less useful, but I still want to try to create them on a regular basis.
I was working on (upcoming) blog post (inspired by one customer issue) on the impact of innodb_default_row_format setting for importing tablespaces (and related checking of the row format really used in both .frm and .ibd files) and found FSP Header description in this old post by Jeremy Cole useful for further checks in the InnoDB source code. MySQL manual is not very informative (and MariaDB KB page is just wrong/incomplete) when describing flags for the table or tablespace, unfortunately, so I've reported MDEV-19523 to get this improved.
If you ever wonder what MariaDB plans to do with InnoDB in the future, please, check MDEV-11633 among other sources.
This week we in Support got customer (on MySQL 8.0.x) complaining that they can not start server any more on Windows 10 after moving datadir to other drive. Check this blog post by my colleague Nil on the reason, explanations and way to fix/prevent this from happening. One of those cases when MySQL Forums give useful hint.
If you build MariaDB (and MySQL) from source on a regular basis (as I do), you may wonder at times how to disable some storage engine plugin at build time (for example, NOT to be affected by some temporary bugs in it when you do not really need it for testing or production use). Save this as hint:
This is what you have to add to cmake command line to prevent building Mroonga, for example. Same approach applies to TokuDB etc. See this KB page also for more details.
I never noted before that "Explain Analyzer" service exists at mariadb.org, but it seems some customers use it and even prefer to share its output instead of plain text EXPLAIN. Just copy/paste any EXPLAIN ...\G there and decide if the result is useful. For Support purposes and queries accessing less than 10 tables or so I'd prefer usual text output.
Yet another public service at mariadb.org I noted this week by pure chance is "MariaDB CI" page with buildbot status and ways to check what is building now, what failed etc. MariaDB Foundation works in a true open manner at all levels.
If you ever cares to find out what exact versions of MariaDB (or MySQL) contain specific commit you can find out using git tag --contains commit_hash command.
I still do not care about Kubernetes at all, but it seems customers start to use it in production, so here is the hint for myself on how run specific command in a running container:
kubectl exec -it <pod> --container <container> -- vi grastate.dat
I may have to write or speak about some details of MySQL and MariaDB architecture soon, so I was looking for related pictures and texts. I found useful details in the following places:
If you are interested in different storage engines and efficiency of indexing, check this blog post by Mark Callaghan.
The last but not the least, I've nominated the following bugs:
Bug #95269 - "binlog_row_image=minimal causes assertion failure". I really wonder why this combination was missed in any regular testing of debug builds (that I hope Oracle does).
Bug #90681 - "MySQL 8.0 fails to install and start from Oracle .debs on debian 9 x86_64". It seems proper documentation is missing for users to know what conflicting packages to remove, what paths to clean up (if any) etc. Maybe this is no longer a concern (I do no use Oracle .deb packages, so I don't know), but in any case having this bug just "Open" helps nobody.
Bug #87312 - "Test main.events_time_zone is fundamentally unstable". It's even more strange to see this bug report about unstable test case "Open" for more than 2 years. Is it really hard to run MTR many times or check the code and improve, or just agree to disable it?
Bug #95411 - "LATERAL produces wrong results (values instead of NULLs) on 8.0.16". This regression bug in optimizer of 8.0.16 (vs 8.0.14) leads to wrong results, but so far nobody cared to verify it (even though it has simple and clear "How to repeat" instructions). This is sad.
for bug of the day on Twitter this week. I've also participated in a discussion there. As a result I ended up reading some recent MEB 8.0 manual pages (and more here). MySQL Enterprise Backup really provides a lot of potentially useful options that mariabackup may benefit from one day...
I spent first two weeks of May properly last year, on vacation in UK. Battersea Park here.
That's more or less all I had written down for further review this week that I am ready top share. Stay tuned for what may come up next week!
Less than one month left until Percona Live. This time the Committee work was a bit unusual. Instead of having one big committee for the whole conference we had a few mini-committees, each responsible for a track. Each independent mini-committee, in turn, had a leader who was responsible for the whole process. I led the MariaDB track. In this post, I want to explain how we worked, which topics we have chosen, and why.
For MariaDB, we had seven slots: five for 50-minutes talks, two for 25-minutes talks and 19 submissions. We had to reject two out of three proposals. We also had to decide how many topics the program should cover. My aim here was to use the MariaDB track to demonstrate as many MariaDB unique features as possible. I also wanted to have as many speakers as possible, considering the number of slots we had available.
The committee agreed, and we tried our best for the program to cover the various topics. If someone sent us two or more proposals, we choose only one to allow more speakers to attend.
We also looked to identify gaps in submitted sessions. For example, if we wanted for a topic to be covered and no one sent a proposal with such a subject, we invited potential speakers and asked them to submit with that topic in mind. Or we asked those who already submitted similar talks to improve them.
In the end, we have five 50-minutes sessions, one MariaDB session in the MySQL track, two 25-minutes sessions, one tutorial, and one keynote. All of them are by different speakers.
Colin started his MySQL career as a Community Engineer back in the MySQL AB times. He worked on numerous MySQL events, both big and small, including Percona Live’s predecessor, O’Reilly’s MySQL Conference and Expo. Colin joined Monty Program Ab, and MariaDB Corporation as a Chief Evangelist, then spent two years as Chief Evangelist at Percona. Now he is an independent consultant at his own company GrokOpen.
Colin will not only talk about unique MariaDB features up to version 10.4, but will also help you try all of them out. This tutorial is a must-attend for everyone interested in MariaDB.
Next day: Wednesday, May 29 – the first conference day – will be the MariaDB Track day.
MariaDB talks will start from the keynote by Vicentiu Ciorbaru about new MariaDB features in version 10.4. He will highlight all the significant additions in this version.
Vicentiu started his career at MariaDB Foundation as a very talented Google Summer of Code student. His first project was Roles. Then he worked a lot on MariaDB Optimizer, bug fixes, and code maintenance. At the same time, he discovered a talent for public speaking, and now he is the face of MariaDB Foundation.
We at the committee had a hard choice: either to accept his 50-minutes session proposal or ask him to make a keynote. This decision was not easy, because a keynote is shorter than 50 minutes. At the same time, though, everyone at the conference will be able to see it. Brand new features of version 10.4 are a very important topic. Therefore, we decided that it would be best to have Vicentiu as a keynote speaker.
Sessions will start with a talk by Alexander Rubin“Opensource Column Store Databases: MariaDB ColumnStore vs. ClickHouse” Alex began his MySQL career as a web developer, then joined MySQL AB as a consultant. He then moved to Percona as Principal Architect. It was our loss when he left Percona to start applying his recommendations himself on behalf of a medical startup VirtualHealth! During his career as a MySQL consultant, he tried all the sexiest database products, loaded terabytes of data into them, ran the deadly intensive loads. He is the one who knows best about database strengths and weaknesses. I would recommend his session to everyone who is considering a column store solution.
Next talk is “Galera Cluster New Features” by Seppo Jaakola. This session is about the long-awaited Galera 4 library. Seppo is one of three founders of Codership Oy: the company which brought us Galera library. Before the year 2007, when the Galera library was first released, MySQL users had to choose between asynchronous replication and asynchronous replication (that’s not a typo). Seppo brought us a solution which allowed us to continue using InnoDB in the style we were used to using while writing to all nodes. The Galera library looks after the data consistency. After more than ten years the product is mature and leaving its competitors far behind. The new version brings us streaming replication technology and other improvements which relax usage limitations and make Galera Cluster more stable. I recommend this session for everyone who looks forward to a synchronous replication future.
At 4:15 pm we will have two MariaDB topics in parallel
“MariaDB and MySQL – What Statistics Optimizer Needs Or When and How Not to Use Indexes” by Sergei Golubchik – a Member of the MariaDB Foundation Board – discovers optimization techniques which are often ignored in favor of indexes. Sergei worked on MySQL, and then on MariaDB, from their very first days. I’ve known him since 2006 when I joined the MySQL team. Each time when I am in trouble to find out how a particular piece of code works, just a couple of words from Sergei help to solve the issue! He has an encyclopedic knowledge on both MariaDB and MySQL databases. In this session, Sergei will explain which statistics optimizer we can use in addition to indexes. While he will focus on specific MariaDB features he will cover MySQL too. Spoiler: these are not only histograms!
Backups in the MySQL track…
In the parallel MySQL track, Iwo Panowicz and Juan Pablo Arruti will speak about backups in their “Percona XtraBackup vs. Mariabackup vs. MySQL Enterprise Backup” Iwo and Juan Pablo are Support Engineers at Percona. Iwo joined Percona two years ago, and now he is one of the most senior engineers in the EMEA team. Linux, PMM, analyzing core files, engineering best practices: Iwo is well equipped to answer all these and many more questions. Juan Pablo works in the American Support team for everything around MariaDB and MySQL: replication, backup, performance issues, data corruption… Through their support work, Iwo and Juan Pablo have had plenty of chances to find out strengths and weaknesses of different backup solutions.
Three tools, which they will cover in the talk, can be used to make a physical backup of MySQL and MariaDB databases, and this is the fastest and best recommended way to work with an actively used server. But what is the difference? When and why should you prefer one instrument over another? Iwo and Juan Pablo will answer these questions.
At the end of the day we will have two 25-minute sessions
Jim Tommaney will present “Tips and Tricks with MariaDB ColumnStore”. Unlike Alex Rubin, who is an end user of ColumnStore databases, Jim is from another side: development. Thus his insights into MariaDB ColumnStore could be fascinating. If you are considering ColumnStore: this topic is a must-go!
Daniel Black will close the day with his talk “Squash That Old Bug”. This topic is the one I personally am looking forward to the most! Not only because I stick with bugs. But, well… the lists of accepted patches which Daniel’s posts to MariaDB and to MySQL servers are impressive. Especially when you know how strict is the quality control for external patches in MariaDB and MySQL! In his talk, Daniel is going to help you to start contributing yourself. And to do it successfully, so your patches are accepted. This session is very important for anyone who has asked themselves why one or another MariaDB or MySQL bug has not been fixed for a long time. I do not know a single user who has not asked that question!
This blog about MariaDB track at Percona Live covers eight sessions, one keynote, one tutorial, 12 speakers, seven mini-committee members – two of whom are also speakers. We worked hard, and continue to work hard, to bring you great MariaDB program.
We have a public holiday here today and it's raining outside for a third day in a row already, so I hardly have anything better to do than writing yet another review of public MySQL bug reports that I've subscribed to recently.
Not sure if these reviews are really considered useful by anyone but few of my readers, but I am still going to try in a hope to end up with some useful conclusions. Last time I've stopped on Bug #94903, so let me continue with the next bug in my list:
Bug #94912 - "O_DIRECT_NO_FSYNC possible write hole". In this bug report Janet Campbell shared some concerns related to the way O_DIRECT_NO_FSYNC (and O_DIRECT) settings for innodb_flush_method work. Check comments, including those by Sunny Bains, where he agrees that "...this will cause problems where the redo and data are on separate devices.". Useful reading for anyone interested in InnoDB internals or using innodb_dedicated_server setting in MySQL 8.0.14+.
Bug #94971 - "Incorrect key file error during log apply table stage in online DDL". Monty Solomon reported yet another case when "online' ALTER for InnoDB table fails in a weird way. The bug is still "Open" and there is no clear test case to just copy/paste, but both the problem and potential solutions (make sure you have "big enough" innodb_online_alter_log_max_size or better use pt-online-schema-change or gh-ost tools) were already discussed here.
Bug #94973 - "Wrong result with subquery in where clause and order by". Yet another wrong results bug with subquery on MySQL 5.7.25 was reported by Andreas Kohlbecker. We can only guess if MySQL 8 is also affected (MariaDB 10.3.7 is not, based on my test results shared below) as Oracle engineer who verified the bug had NOT card to check or share the results of this check. What can be easier than running this (a bit modified) test case on every MySQL major version and copy pasting the results:
MariaDB [test]> SELECT hex(bitField) from ReferenceB where id in (select id as y0_ from ReferenceB where refType='JOU') order by externalLink asc; +---------------+ | hex(bitField) | +---------------+ | 0 | | 0 | +---------------+ 2 rows in set (0.028 sec)
But we do not see anything like that in the bug report... This is sad.
Bug #94994 - "Memory leak detect on temptable storage engine". Yet another memory leak (found with ASan) reported by Zhao Jianwei, who had also suggested a patch.
Bug #95008 - "applying binary log doesn't work with blackhole engine tables". This bug was reported by Thomas Benkert. It seems there is a problem to apply row-based events to BLACKHOLE table and this prevents some nice recovery tricks from working.
Bug #95020 - "select no rows return but check profile process Creating sort index". Interesting finding from cui jacky. I can reproduce this with MariaDB as well. It seems we either have to define some new stage or define "Creating sort index" better than in the current manual. This:
The thread is processing a SELECT that is resolved using an internal temporary table.
is plain wrong in the case shown in the bug report IMHO.
Bug #95040 - "Duplicately remove locks from lock_sys->prdt_page_hash in btr_compress". One of those rare cases when Zhai Weixiang does not provide the patch, just suggests the fix based on code review :)
Bug #95045 - "Data Truncation error occurred on a write of column 0Data was 0 bytes long and". This really weird regression bug in MySQL 8.0.14+ was reported by Adarshdeep Cheema. MariaDB 10.3 is surely not affected.
Bug #95049 - "Modified rows are not locked after rolling back to savepoint". Bug reporter, John Lin, found that fine MySQL manual does not describe the real current implementation. Surprise!
Bug #95058 - "Index not used for column with IS TRUE or IS FALSE operators". Take extra care when using BOOLEAN columns in MySQL. As it was noted by Monty Solomon, proper index is NOT used when you try to check BOOLEAN values as manual suggests, using IS TRUE or IS FALSE conditions. Roy Lyseng explained how such queries are threated internally, but surely there is a better way. MariaDB 10.3.7 is also affected, unfortunately.
Bug #95064 - "slave server may has gaps in Executed_Gtid_Set when a special case happen ". Nice bug report from yoga yoga, who had also contributed a patch. Parallel slave can easily get out of sync with master in case of lock wait timeout and failed retries. Again, we do NOT see any check if MySQL 8 is affected, unfortunately.
Bug #95065 - "Strange memory management when using full-text indexes". We all know that InnoDB FULLTEXT indexes implementation is far from perfect. Now, thanks to Yura Sorokin, we know also about a verified memory leak bug there that may lead to OOM killing of MySQL server.
Bug #95070 - "INSERT .. VALUES ( .., (SELECT ..), ..) takes shared lock with READ-COMMITTED". Seunguck Lee found yet another case of InnoDB locking behavior that MySQL manual does not explain. The bug is still "Open" for some reason.
Bug #95115 - "mysqld deadlock of all client threads originating from 3-way deadlock". It took some efforts for bug reporter, Sandeep Dube, and other community users (mostly Jacek Cencek) to attract proper attention to this bug from proper Oracle developer, Dmitry Lenev, until it ended up "Verified" based on code review. We still can not be sure if MySQL 8 is also affected.
That's all for now. I have few more new bug reports that I monitor, but I do not plan to continue with this kind of reviews in upcoming few months in this blog. I hope I'll get a reason soon to write different kind of posts, with more in depth study of various topics...
In any case you may follow me on Twitter for anything related to recent interesting or wrongly handled MySQL bug reports.
This view of Chelsea from our apartment at Chelsea Cloisters reminds me that last year I spent spring holiday season properly - no time was devoted to MySQL bugs :)
Do not use O_DIRECT_NO_FSYNC value for innodb_flush_method if your redo logs are located on different device than your data files. Just don't.
Some Oracle engineers who process bugs still do not care to check if all supported major versions are affected and/or share the results of such checks in public.
There are still many details of InnoDB locking to study, document properly and maybe fix.
I am really concerned with the state of MySQL optimizer. We see all kinds of weird bugs (including regressions) and very few fixes in each maintenance release.
Oracle released minor MySQL Server versions in all supported branches on April 25, 2019. MySQL 5.7.26 is just one of them, but recently I prefer to ignore MySQL 8 releases (after checking that I can build them from source code at least somewhere, even if it takes 18G+ of disk space and that they work in basic tests), as there are more chances for MySQL 5.7 bug fixes to affect me (and customers I care about) directly.
So, in this yet another boring blog post (that would never be a reason for any award) I plan to concentrate on bugs reported in public MySQL bugs database and fixed in MySQL 5.7.26. As usual I name bug reporters explicitly and give links to their remaining currently active bug reports, if any. This time the list is short enough, so I do not even split it by categories:
Bug #93164 - "Memory leak in innochecksum utility detected by ASan". This bug was reported by Yura Sorokin from Percona, who also had contributed a patch (for some reason this is not mentioned in the official release notes).
Bug #90402 - "innodb async io error handling in io_event". Wei Zhao found yet another case when wrong data type was used in the code and I/O error was not handled, and this could lead even to crashes. He had submitted a patch.
Bug #89126 - "create table panic on innobase_parse_hint_from_comment". Nice bug report with a patch from Yan Huang. Note also detailed analysis and test case provided by Marcelo Altmann in the comment. It's a great example of cooperation of all sides: Oracle MySQL developers, bugs verification team, bug reporter and other community users.
Bug #92241 - "alter partitioned table add auto_increment diff result depending on algorithm". Yet another great finding from Shane Bester himself!
Bug #94247 - "Contribution: Fix fractional timeout values used with WAIT_FOR_EXECUTED_GTI ...". This bug report was created based on pull request from Dirkjan Bussink, who had suggested a patch to fix the problem. Note the comment from Shlomi Noach that refers to Bug #94311 (still private).
Bug #85158 - "heartbeats/fakerotate cause a forced sync_master_info". Note MTR test case contributed by Sveta Smirnova and code analysis in a comment from Vlad Lesin (both from Percona at that time) in this bug report from Trey Raymond.
Bug #92690 - "Group Replication split brain with faulty network". I do not care about group replication (I have enough Galera in my life instead), but I could not skip this report by Przemyslaw Malkowski from Percona, with detailed steps on how to reproduce. Note comments from other community members. Yet another case to show that good bug reports attract community feedback and are fixed relatively fast.
Bug #93750 - "Escaping of column names for GRANT statements does not persist in binary logs". Clear and simple bug report from Andrii Ustymenko. I wonder why it was not found by internal testing/QA. Quick test shows that MariaDB 10.3.7, for example, is not affected:
c:\Program Files\MariaDB 10.3\bin>mysql -uroot -proot -P3316 test Welcome to the MariaDB monitor. Commands end with ; or \g. Your MariaDB connection id is 9 Server version: 10.3.7-MariaDB-log mariadb.org binary distribution
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
Bug #73936 - "If the storage engine supports RBR, unsafe SQL statementes end up in binlog". Nice bug report with MTR test case by Santosh Praneeth Banda. Note that last comment about the fix mentions only MySQL 8.0.15, not a single work about the fix in MySQL 5.7.26 (or anything about MySQL 5.6.x while the bug was reported for 5.6).
Bug #93341 - "Check for tirpc needs improvement". The need for improvement of CMake check was noted by Terje Røsten.
Bug #91803 - "mysqladmin shutdown does not wait for MySQL to shut down anymore". This regression bug (without a "regression" tag) was reported by Christian Roser.
Bug #91541 - ""Flush status" statement adds twice to global values ". Yura Sorokin contributed a detailed anlysis, MTR test case and a patch in this bug reported by Carlos Tutte.
Bug #90351 - "GLOBAL STATUS variables drift after rollback". Zsolt Parragi contibuted a patch to this bug found and reported by Iwo P. For some reason this contribution is not highlighted in the release notes.
Bug #81441 - "Warning about localhost when using skip-name-resolve". One of many bug reports from Monty Solomon in which he (and other community members like Jean-François Gagné) had to spend a lot of efforts and fight with a member of bugs verification team to get the bug accepted as a real code bug and then get it fixed in all versions affected.
Bug #90902 - "Select Query With Complex Joins Leaks File Handles". This bug was reported by James Wilson. I still wonder if MySQL 5.6 was affected. Bug reports says nothing about this (while I expect all supported GA versions to be checked when the bug is verified, and the results of such check clearly documented).
The future looks bright for MySQL 5.7
Consider upgrade to 5.7.26 if you use complex joins, partitioned tables with auto_increment columns or rely on InnoDB or replication a lot.
It's good to see crashing bugs that do not end up as hidden/"security", maybe because they are reported with patches...
It's good to see examples of cooperation of several community users contributing to the same bug report!
Percona engineers contribute a lot to MySQL, both in form of bug reports, patches and by helping other community users to make their point and get their bugs fixed fast.
There are still things to improve in a way Oracle egnineers handle bugs verification, IMHO.
It's also a bit strange to see only one optimizer-related fix in this release. It means that either MySQL optimizer is already near perfect and there are no bugs to fix (check yourself, but I see 123 bugs here), or that nobody cares that much about MySQL optimizer in 5.7 these days.
It seems for some bugs fixed in previous MySQL 8.0.x minor release there is no extra check/updates in public comments about the versions with the fix when it is released in MySQL 5.6 or 5.7.