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Displaying posts with tag: information_schema (reset)
MySQL & InnoDB Disk Space

Yesterday, Bhuvanesh published an article about how to verify the difference between allocated diskspace for a tablespace and the the data in it.

I commented with an old post explaining how to get some similar info only using SQL in case you don’t have filesystem access.

And finally, my friend Bill Karwin, commented how this info is not always accurate. Which, of course, I agree with.

This is why, I checked …

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MySQL: CPU information from SQL

Do you know that it’s possible to get information from the CPUs of your MySQL Server from SQL ?

If you enable the status for the  INNODB_METRICS table in INFORMATION_SCHEMA, you will be able to query CPU information.

First, check if those status are enabled:

MySQL> SELECT name, subsystem, status 
FROM INFORMATION_SCHEMA.INNODB_METRICS where NAME like 'cpu%';
+---------------+-----------+----------+
| name | subsystem | status |
+---------------+-----------+----------+
| cpu_utime_abs | cpu | disabled |
| cpu_stime_abs | cpu | disabled |
| cpu_utime_pct | cpu | disabled |
| cpu_stime_pct | cpu | disabled |
| cpu_n | cpu | disabled |
+---------------+-----------+----------+
5 rows in set (0.00 sec)
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How to grant privileges to users in MySQL 8.0

It seems, that this is a question that regularly shows up in forums or stackoverflow.

To start, let’s highlight the fact that in MySQL 8.0 it’s not any more possible to create a user directly from the GRANT command (ERROR 1410 (42000): You are not allowed to create a user with GRANT).

This means that to grant some privileges, the user must be created first.

Let’s create a user ‘user1‘ with ‘ChangeMe‘ as password that the user will have to change:

mysql> create user 'user1' identified by 'ChangeMe' password expire;
Query OK, 0 rows affected (1.35 sec)

Let’s try to connect to MySQL using that new created user:

 $ mysql -u …
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MySQL 8.0 and keywords

As you know, MySQL uses some keywords and some of them are also reserved.

Let’s have a look how to deal with that:

mysql> create table WRITE (id int auto_increment primary key, varying varchar(10), than int);
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your
MySQL server version for the right syntax to use near 'WRITE (id int auto_increment primary key,
varying varchar(10), than int)' at line 1

OK, it seems WRITE is a keyword I cannot use as table name. I’ve then two choices:

  • rename the table to something else like WRITE_TBL
  • use back-ticks (`) around the table like `WRITE`

Let’s use the first option:

mysql> create table WRITE_TBL (id int auto_increment primary key, varying varchar(10), than …
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pre-FOSDEM MySQL Day 2019

For the third year in a row, we will take advantage of the mass presence of our MySQL Engineers during FOSDEM to organize the pre-FOSDEM MySQL Day.

The program of this 3rd edition is already on track, thank you to all the speakers who already confirmed their participation.

Start End Event Speaker Company Topic
Friday 1st February
09:30 10:00 MySQL Community Team Welcome
10:00
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MySQL: size of your tables – tricks and tips

Many of you already know how to retrieve the size of your dataset, schemas and tables in MySQL.

To summarize, below are the different queries you can run:

Dataset Size

I the past I was using something like this :

But now with sys schema being installed by default, I encourage you to use some of the formatting functions provided with it. The query to calculate the dataset is now:

SELECT sys.format_bytes(sum(data_length)) DATA,
       sys.format_bytes(sum(index_length)) INDEXES,
       sys.format_bytes(sum(data_length + index_length)) 'TOTAL SIZE'
FROM information_schema.TABLES ORDER  BY data_length + index_length;

Let’s see an example:

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Basic Internal Troubleshooting Tools for MySQL Server Webinar: Q & A

In this blog, I will provide answers to the Q & A for the Basic Internal Troubleshooting Tools for MySQL Server webinar.

First, I want to thank everybody for attending my February 15, 2018, webinar on troubleshooting tools for MySQL. The recording and slides for the webinar are available here. Below is the list of your questions that I was unable to answer fully during the webinar.

Q: How do we prevent the schema prefix from appearing in the show create view. This is causing issue with restore on another server with a different DB. See the issue …

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MySQL 8.0: Improvements to Information_schema

Coinciding with the new native data dictionary in MySQL 8.0, we have made a number of useful enhancements to our INFORMATION_SCHEMA subsystem design in MySQL 8.0. In this post I will first go through our legacy implementation as it has stood since MySQL 5.1, and then cover what’s changed.…

Useful queries on MySQL information_schema

MySQL information_schema comes with useful information about the database instance, status, … etc. which is needed for daily DBA work.
There are some simple queries on the information_schema that I use on my daily basis in which I’m writing this post for my reference and maybe a good reference for someone else too …

Finding tables without Primary or Unique Keys:

PKs are so important, especially, for InnoDB tables as MySQL uses PKs as a clustered index and having no PKs might lead to severe performance problems.

Also having no PKs is one of the main causes of slave lagging problems mainly when using RBR (Row-Based Replication), e.g. if a delete statement on the master will delete 1 million rows on a table without PK, a full table scan will take place. This “might” not be a problem on the master but on the slave 1 million full table scan will take place – because changes to the individual rows are being …

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Checking table definition consistency with mysqldiff

Data inconsistencies in replication environments are a pretty common. There are lots of posts that explain how to fix those using pt-table-checksum and pt-table-sync. Usually we only care about the data but from time to time we receive this question in support:

How can I check the table definition consistency between servers?

Replication also allow us to have different table definition between master and slaves. For example, there are some cases that you need some indexes on slaves for querying purposes but are not really needed on the master. There are some other cases where those differences are just a mistake that needs to be fixed.

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