In this blog post, we’ll look at MySQL 8.0 general tablespaces.
Introduction
MySQL 8.0 (the DMR version is available now) has two great features (among others):
- The new data dictionary completely removed *.frm files, which is great
- The ability to create a tablespace and assign a group of tables to it (originally introduced in 5.7).
With those two options, we can use MySQL for creating multi-tenant environments with a “schema per customer” approach.
Schema per Customer with MySQL 8.0
Using schema per customer with older MySQL versions presents issues … namely the number of files. (I’ve described schema per customer approach in MySQL in an older blog post.) Let’s say you are hosting a Drupal-based site for your customers, and you create a new database (AKA “schema”) per each customer. You do not want to create one schema for all because each customer wants to extend Drupal and use plugins that will create their own unique set of tables. With tablespace per table and an FRM file, 10K customers will end up with:
- 65 tables per schema,
- Two files per table, and
- 10K schemas
. . . or a grand total of 1.3 million files!
With MySQL 8.0, we can create a tablespace file per each schema and place those tablespace files in a specific set of directories. For example, if we have demo, test and production accounts, we can create a set of directories (outside of the MySQL datadir) and place tablespaces inside them. With no FRM files, we will only have 10 thousands of files, evenly split across multiple locations.
Example:
mysql> create database if not exists drupal_customer_name; Query OK, 1 row affected (0.00 sec) mysql> CREATE TABLESPACE drupal_customer_name ADD DATAFILE '/var/lib/mysql_datafiles/drupal_demo/drupal_customer_name.ibd' Engine=InnoDB; Query OK, 0 rows affected (0.16 sec) mysql> use drupal_customer_name; Database changed mysql> create table t(i int) ENGINE=InnoDB TABLESPACE drupal_customer_name; Query OK, 0 rows affected (0.13 sec) mysql> create table t1(i int) ENGINE=InnoDB TABLESPACE drupal_customer_name; Query OK, 0 rows affected (0.00 sec)
Now let’s look at the directory:
ls -lah /var/lib/mysql_datafiles/drupal_demo/ -rw-r----- 1 mysql mysql 144K Sep 26 00:58 drupal_customer_name.ibd
The downside of this approach is that the “create tables” command should have the tablespace name in it. I’ve created a sample “deploy” script to create a new schema for a customer:
customer_name="my_drupal_customer"
mysql -f -vvv -e "create database if not exists $customer_name;
CREATE TABLESPACE $customer_name ADD DATAFILE '/var/lib/mysql_datafiles/drupal_demo/${customer_name}.ibd'
engine=InnoDB;"
cat drupal.sql | sed -e "s/ENGINE=InnoDB/ENGINE=InnoDB TABLESPACE $customer_name/g"|mysql $customer_nameSize and Timing
In the next post, I plan to benchmark the performance of millions of tables with MySQL 8.0 and tablespace file per database. Here, I’ve compared the create table performance between MySQL 5.7 (with FRM and file per table), MySQL 8.0 with a file per table (FRMs are gone) and MySQL 8.0 with a file per database. Time to create 1000 databases for Drupal (no data), 65 tables in each database:
- MySQL 5.7, file per table: 3m21.819s
- MySQL 8.0, file per table: 2m54.358s
- MySQL 8.0, file per database: 1m55.133s
What about the size on disk? It did not change much. Actually, the size on disk for the blank tables (no data) is more in MySQL 8.0:
- 8.0: 10M (10485760 bytes) per 65 blank tables (Drupal)
- 5.7: 9.2M (9280821 bytes) per 65 blank tables, including FRM files
With 10K schemas, it is 100G just to store tablespaces (schema overhead). At the same time, it is not 100% overhead: InnoDB creates 112K+ the tablespace file right away (it depends upon the table structure). When the data is loaded it will use this reserved space.
Tablespace supports compression as well: CREATE TABLESPACE … ADD DATAFILE ‘…’ FILE_BLOCK_SIZE = 8192 Engine=InnoDB; CREATE TABLE … ENGINE=InnoDB TABLESPACE … ROW_FORMAT=COMPRESSED;
New Data Dictionary
MySQL 8.0 uses a new transactional data dictionary.
MySQL Server 8.0 now incorporates a global data dictionary containing information about database objects in transactional tables. In previous MySQL releases, dictionary data was stored in metadata files and nontransactional system tables.
That also means that all old metadata files are gone: no .frm, .par, .trn, .trg files. In addition tables inside a MySQL database are not using MyISAM tables anymore. The new installation has no single MyISAM table, although the MyISAM engine is supported:
Welcome to the MySQL monitor. Commands end with ; or g. Your MySQL connection id is 2299 Server version: 8.0.0-dmr MySQL Community Server (GPL) Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type 'help;' or 'h' for help. Type 'c' to clear the current input statement. mysql> select count(*) from information_schema.tables where engine = 'MyISAM'; +----------+ | count(*) | +----------+ | 0 | +----------+ 1 row in set (0.03 sec) mysql> select count(*), engine from information_schema.tables where table_schema = 'mysql' group by engine; +----------+--------+ | count(*) | ENGINE | +----------+--------+ | 2 | CSV | | 30 | InnoDB | +----------+--------+ 2 rows in set (0.00 sec)
Conclusion
FRM free installation looks great (performance testing of it is my next step). I would also love to see some additional features in MySQL 8.0:
- Easier tablespace level manipulations, i.e. “optimize tablespace” to re-claim space in the general tablespace file; add “if exists / if not exists” to create/drop tablespace
- Much smaller “reserved” space: if the data dictionary is stored elsewhere, we can create a one-page file (16K) + table structure.
References
- MySQL 8.0 Manual
- Create general tablespace syntax in MySQL 8.0
- New data dictionary in MySQL 8.0 and data dictionary limitations
Please note: MySQL 8.0 is not production ready and only available for preview.