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 …

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 …

While working in Support, I noticed that probably at least once a week I have to use or mention lsof utility in some context. This week, for example, we had a customer trying to find out if his mysqld process running is linked with tcmalloc library. He started it different ways, using LD_PRELOAD directly and --malloc-lib option of mysqld_safe script etc, but wanted to verify that his attempts really worked as expected. My immediate comment in the internal chat was: "Just let them run lsof -p `pidof mysqld` | grep mall and check!" My MariaDB 10.2 instance uses jemalloc and this can be checked exactly the same way:
openxs@ao756:~/dbs/maria10.2$ ps aux | grep mysqld...
openxs    4619  0.0  0.0   4452   804 pts/2    S    …

While MySQL 8.0.x hardly has much impact on my regular work, recent MySQL 5.7.20 release is something to check carefully. MySQL 5.7 is widely used in production, as a base for Percona Server 5.7, some features may be merged into MariaDB 10.x etc. So, here is my review of some community reported bugs that were fixed in recently released MySQL 5.7.20, based on the release notes.

Usually I start with InnoDB bug fixes, but in 5.7.20 several related fixes were made only to bugs reported internally. So, this time I have to start with partitioning:

• Bug #86255 - First one to write about, and the bug report is …

This week is special and full of anniversaries for me. This week 5 years ago I left Oracle behind and joined Percona... Same week 5 years ago I had written something about MySQL in this blog for the first time in my life. 5 years ago I've created my Facebook account that I actively (ab)use for discussing work-related issues. So, to summarize, it's a five years anniversary of my coming out as a MySQL Entomologist, somebody who writes and speaks about MySQL and bugs in MySQL in public! These 5 years were mostly awesome.

I decided to celebrate with yet another post in this relatively new series and summarize in short what interesting things I studied, …

In part 1 and part 2 of this blog series, I showed how a DBA could configure MySQL or MariaDB to automatically drop old partitions. Some readers mentioned that they would also like for new partitions to be automatically created. In this blog post, I will show a stored procedure that can automatically create new partitions, and I will tie ... Read More

In a previous blog post, I showed how a DBA could configure MySQL or MariaDB to automatically drop old partitions. Some readers provided some feedback on some issues that they’ve run into while doing similar operations. Specifically: It can sometimes help to maintain an empty first partition when partitioning by dates, since partition pruning cannot always eliminate the first partition. ... Read More

A MariaDB Support customer recently asked how they could automatically drop old partitions after 6 months. MariaDB and MySQL do not have a mechanism to do this automatically out-of-the-box, but it is not too difficult to create a custom stored procedure and an event to call the procedure on the desired schedule. In this blog post, I will show one ... Read More

In this blog, we’ll quickly look at MySQL partitioning.

Partitioning is a way in which a database (MySQL in this case) splits its actual data down into separate tables, but still get treated as a single table by the SQL layer.

When partitioning, it’s a good idea to find a natural partition key. You want to ensure that table lookups go to the correct partition or group of partitions. This means that all SELECT, UPDATE, DELETE should include that column in the WHERE clause. Otherwise, the storage engine does a scatter-gather, and queries ALL partitions in a UNION that is not concurrent.

Generally, you must add the partition key into the primary key along with the auto increment, i.e., PRIMARY KEY (part_id,id). If you …

Sometimes MySQL surprises you in ways you would have never imagined.

Would you think that the order in which the indexes appear in a table matters?
It does. Mind you, not the order of the columns - the order of the indexes.
MySQL optimizer can, in specific circumstances, take different paths, sometimes with nefarious effects.


Please consider the following table:

CREATE TABLE `mypartitionedtable ` (
  `HASH_ID` char(64) NOT NULL,
  `RAW_DATA` mediumblob NOT NULL,
  `EXPIRE_DATE` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  KEY `EXPIRE_DATE_IX` (`EXPIRE_DATE`),
  KEY `HASH_ID_IX` (`HASH_ID`)
) ENGINE=TokuDB DEFAULT CHARSET=latin1 ROW_FORMAT=TOKUDB_UNCOMPRESSED
/*!50100 PARTITION BY RANGE (UNIX_TIMESTAMP(EXPIRE_DATE))
(PARTITION p2005 VALUES LESS THAN (1487847600) ENGINE = …