Let me start with a little story. You sit in your house near the fireplace in the living room and need a book from the library… Eh, no, sorry, wrong century. You’re building a robotic arm that will open your beer or brew your coffee or supply you with whatever other drinks of your choice… while you’ll be building the next robotic arm. So, you — soldering iron in one hand and Arduino in another — ask your little brother to bring a box with specific resistors (that you unexpectedly run out of) from the cellar. The problem — your brother is small and cannot tell a resistor from a respirator. …

Continue reading “MariaDB 10.1.1: engine_condition_pushdown flag deprecated”

I don’t think it’ll surprise anybody if I say that MariaDB or MySQL server knows a lot more about server system variables, then just their values. Indeed, every variable can be session or global only, read-only or writable, it has an associated help text (that is printed on mysqld –help –verbose), certain variables only accept values from a given set of strings (this set of allowed values is also printed in mysqld –help –verbose since MariaDB 10.1.0), numeric variables have lower and upper range boundaries of valid values (that are never printed anywhere), and so on. I always thought it’s kind of a waste that there is no way to query this information. …

Continue reading “MariaDB 10.1.1: system variables and their metadata”

Introduction

When you e.g. delete rows, these rows are just marked as deleted not really physically deleted from indexes and free space introduced is not returned to operating system for later reuse. Purge thread will physically delete index keys and rows, but still free space introduced is not returned to operating system and this operation can lead holes on page. If you have variable length rows, this could lead to situation where this free space can’t be used for new rows (if these rows are larger than old ones). User may use OPTIMIZE TABLE or ALTER TABLE <table> …

Continue reading “MariaDB 10.1.1: Defragmenting unused space on InnoDB tablespace”

Introduction

Online DDL is a new feature in MariaDB 10.0. Online DDL is processed through below 4 tasks in sequence.

InnoDB::ha_prepare_inplace_alter_table(..)
InnoDB::ha_inplace_alter_table(..)
InnoDB::ha_commit_inplace_alter_table(..)
mysql_rename_table(..)

InnoDB storage engine allocates temporal memory buffer for transaction logging in phase 1 where row changes during this phase are logged. Size of this buffer is at start sort_buffer_size and it can be grown up to innodb_online_alter_log_max size. During phase 2 thread processing the ALTER statement will copy old table’s rows to a new altered table. After this MariaDB will take exclusive lock for target table and applies row log buffer to the new altered table. …

Continue reading “MariaDB 10.1.1: Monitoring progress and temporal memory usage of Online DDL in InnoDB”

One of the most popular plugin types both in MariaDB and MySQL is INFORMATION_SCHEMA plugin type. INFORMATION_SCHEMA plugins add new tables to the INFORMATION_SCHEMA. There are lots of INFORMATION_SCHEMA plugins, because they can be used to show just anything to the user and are very easy to write.

MariaDB 10.1.1 comes with nine INFORMATION_SCHEMA plugin:

Feedback — shows the anonymised server usage information and can optionally send it to the configured url.
Locales — lists compiled-in server locales, implemented by Roberto Spadim
METADATA_LOCK_INFO — Lists metadata locks in the server.

…

Continue reading “MariaDB 10.1.1: FLUSH and SHOW for plugins”

The MariaDB Team will have the following presentations at Percona Live London:

Engine Independent Table Statistics in MariaDB: Let the optimizer know your data by Sergei Golubchik
MySQL in the Hosted Cloud by Colin Charles

We’ll also be at the community meetups and all around the conference during those couple of days. Don’t forget that if you haven’t already registered, you can use discount code ‘PLUK14CC’ for a £20 discount.

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Continue reading “Meet some of the MariaDB Team at Percona Live London”

Every now and then there is a need to execute certain SQL statements conditionally. Easy, if you do it from your PHP (or Java or whatever) application. But if all you have is pure SQL? There are two techniques that MariaDB and MySQL use in the mysql_fix_privilege_tables.sql script (applied by mysql_upgrade tool).

Create a stored procedure with IF statements inside, call it once and drop it. This requires the user to have the CREATE ROUTINE privilege and mysql.proc table must exist and be usable (which is not necessarily true — we’re doing it from mysql_upgrade, right?).
Use dynamic SQL, like
SET @str = IF (@have_csv = ‘YES’,
‘CREATE TABLE IF NOT EXISTS general_log (
event_time TIMESTAMP(6) NOT NULL,
user_host MEDIUMTEXT NOT NULL,
thread_id BIGINT(21) UNSIGNED NOT NULL,
server_id INTEGER UNSIGNED NOT NULL,
command_type VARCHAR(64) NOT NULL,
argument MEDIUMTEXT NOT NULL
) engine=CSV CHARACTER SET utf8 comment=”General log”‘,
‘SET @dummy = 0’);

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Continue reading “MariaDB 10.1.1: Compound statements”

Yes! In MariaDB 10.1.1 tables in PERFORMANCE_SCHEMA do not use .frm files. These files are not created, not read — in fact, PERFORMANCE_SCHEMA tables never touch the disk at all.

This became possible due to a lesser-known feature of MariaDB — new table discovery (“old table discovery” was implemented in MySQL for NDB Cluster in 2004), implemented in MariaDB 10.0.2. Instead of reading and parsing .frm files, MariaDB simply asks PERFORMANCE_SCHEMA table, what structure it has, and because these tables always have a fixed structure, the table directly returns it to MariaDB with no need for any external data dictionary. …

Continue reading “MariaDB 10.1.1: no more .frm’s for performance_schema tables”