Anyone familiar with Oracle performance tuning knows about ASH , aka active session history. ASH saves a history of every session that is active every collection, which by default is once per second. Once per second is fast enough to give a clear view of database load.

The ASH data comes from v$session which is a structure that contains information on every connection and shows which connections are active, what SQL they are running (SQL_ID) and if they are runnable on CPU or waiting on a wait_event for some resource like an I/O to complete or a lock or latch. It’s a pretty simple select query on v$session to select who is active,  their wait_event and SQL_ID.

On Oracle that gives us a query like:

select sid||':'||serial# session_id,
       username,
       s.sql_id||':'||sql_child_number sqlid,
       decode(state, 'WAITING', wait_class||':'||event, 'CPU') event
from v$session s
where   (( s.wait_time != 0  /* on CPU  */ …

On 22nd March 2022 08:43 UTC, we became aware of the issue affecting Okta, a third-party identity provider that Percona uses for https://id.percona.com. Initially, there was no statement from Okta, so our Security Operations team reviewed the information available from LAPSUS$ and other public sources.

Based on the public information available about the issue, we evaluated the potential exposure to Percona and determined that the impact was minimal. Percona uses Okta integrations so https://id.percona.com can be used to authenticate against Percona’s deployments of:

• forums.percona.com (Discourse)
• percona.service-now.com (ServiceNow) 
• portal.percona.com (Dashboard portal interface where users & clients can add their PMM integration). 

Integrations of …

How does one use  NESTING_EVENT_ID?

Below I’ve selected from  events_waits_history_long for a single thread, but none of the  NESTING_EVENT_ID values show up in EVENT_ID or END_EVENT_ID.

To simplify things , I’m just showing the data for one THREAD_ID listed in order of TIMER_START.

mysql>  select 
            THREAD_ID,
            EVENT_ID,
            END_EVENT_ID,
            NESTING_EVENT_ID,
            NESTING_EVENT_TYPE,
            EVENT_NAME,
            SOURCE,
            TIMER_WAIT,
            SPINS,
            OBJECT_SCHEMA,
            OBJECT_NAME,
            INDEX_NAME,
            OBJECT_TYPE,
            OBJECT_TYPE,
            OBJECT_INSTANCE_BEGIN,
            OPERATION,
            NUMBER_OF_BYTES,
            FLAGS 
 from 
           performance_schema.events_waits_history_long 
 where 
            THREAD_ID in ( select max(thread_id) from performance_schema.events_waits_history_long where …

A short introduction to the new MySQL Shell for VS Code extension.

PlanetScale Rewind is the world’s first data migration time machine. Revert changes to your database after a migration with no downtime and zero data loss.

Read the full story

Learn how we used VReplication to allow for migration reverts with data retention.

Read the full story

For a very long part of its history, MySQL replication has been limited in terms of performance. Because there was no way of knowing if transactions or updates were independent, the updates had to be executed on a replica following the exact same sequence of operations as on the primary server. The only way to guarantee the same sequence of operations on the replica was to use a single thread. In this post, we’ll do a dive into the MySQL multi-threaded replication (MTR) implementation and explore the available tuning options.

MTR is the culmination of the evolution in the development of parallel replication which followed the path:

1. Single-threaded replication
2. Per-database replication
3. Logical clock replication

We’ll leave aside, for now, the recent dependency tracking feature.

Context

Before we discuss the multi-threaded implementation, let’s review in …

I record this for posteriority without much comment.

The error message “Truncated incorrect DOUBLE value” when issued by MySQL can be a confused parser, and masks unintended barely legal syntax:

kris@localhost [kris]> select * from testtable;
+----+------+
| id | d    |
+----+------+
|  1 | eins |
|  2 | zwei |
|  3 | drei |
+----+------+
3 rows in set (0.00 sec)
 
kris@localhost [kris]> update testtable set d="vier" and id = 4 where id = 3;
ERROR 1292 (22007): Truncated incorrect DOUBLE value: 'vier'

The actual problem here is the incorrect use of and in the set-clause of the update statement when a comma was intended.

kris@localhost [kris]> update testtable set d="vier", id = 4 where id = 3;
Query OK, 1 row affected (0.02 sec)
Rows matched: 1  Changed: 1  Warnings: 0

Technically, an and is possible and legal, if you …

When using MySQL with Python, you may want to use the mysqlclient library, which is what most people do and which will work just fine. Or you are using the official MySQL 8 Connector/Python package, which will behave slightly differently, but maybe supports the unique MySQL 8 feature already that is not in mysqlclient, yet.

Your SQL may be hand-writtten, or it may be generated using SQL Alchemy, Django or some other package. If the latter is the case, it may be useful to be able to see the actual SQL string that has been sent to the database in order to facilitate interactive debugging.

Using mysqlclient

If you are using mysqlclient with Python, the class internally sends the SQL to the server in a method _query(self, q) in the Cursor class ( …

In MySQL, the @@sql_mode parameter should generally use ONLY_FULL_GROUP_BY. If it doesn’t include it and you don’t have the ability to change the database parameters, you can use a MySQL PSM (Persistent Stored Module), like:

Create the set_full_group_by procedure:

-- Drop procedure conditionally on whether it exists already.
DROP PROCEDURE IF EXISTS set_full_group_by;

-- Reset delimter to allow semicolons to terminate statements.
DELIMITER $$

-- Create a procedure to verify and set connection parameter.
CREATE PROCEDURE set_full_group_by()
  LANGUAGE SQL
  NOT DETERMINISTIC
  SQL SECURITY DEFINER
  COMMENT 'Set connection parameter when not set.'
BEGIN

  /* Check whether full group by is set in the connection and
     if unset, set it in the scope of the connection. */
  IF NOT EXISTS
    (SELECT NULL
     WHERE  REGEXP_LIKE(@@SQL_MODE,'ONLY_FULL_GROUP_BY'))
  THEN
    SET SQL_MODE=(SELECT CONCAT(@@sql_mode,',ONLY_FULL_GROUP_BY'));
  END IF; …