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Displaying posts with tag: storage engine (reset)
MySQL 101: Tuning MySQL After Upgrading Memory

In this post, we will discuss what to do when you add more memory to your instance. Adding memory to a server where MySQL is running is common practice when scaling resources.

First, Some Context

Scaling resources is just adding more resources to your environment, and this can be split in two main ways: vertical scaling and horizontal scaling.

Vertical scaling is increasing hardware capacity for a given instance, thus having a more powerful server, while horizontal scaling is adding more servers, a pretty standard approach for load balancing and sharding.

As traffic grows, working datasets are getting bigger, and thus we start to suffer because the data that doesn’t fit into memory has to be retrieved from disk. This is a costly operation, even with modern NVME drives, so at some point, we will need to deal with either of the scaling solutions we mentioned.

In this case, we will discuss adding more …

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MySQL ERROR 1034: Incorrect Key File on InnoDB Table

Sometimes, you may experience “ERROR 1034: Incorrect key file” while running the ALTER TABLE or CREATE INDEX command:

mysql> alter table ontime add key(FlightDate);
ERROR 1034 (HY000): Incorrect key file for table 'ontime'; try to repair it

As the error message mentions key file, it is reasonable to assume we’re dealing with the MyISAM storage engine (the legacy storage engine which used to have such a thing), but no, we can clearly see this table is InnoDB!

When the error message in MySQL is confusing or otherwise unhelpful, it is a good idea to check the MySQL error log:

2019-02-24T02:02:26.100600Z 9 [Warning] [MY-012637] [InnoDB] 1048576 bytes should have been written. Only 696320 bytes written. Retrying for the remaining bytes.
2019-02-24T02:02:26.100884Z 9 [Warning] [MY-012638] [InnoDB] Retry attempts for writing partial data failed.
2019-02-24T02:02:26.100894Z 9 [ERROR] [MY-012639] [InnoDB] Write to file …
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InnoDB Flushing in Action for Percona Server for MySQL

As the second part of the earlier post Give Love to Your SSDs – Reduce innodb_io_capacity_max! we wanted to put together some concepts on how InnoDB flushing works in recent Percona Server for MySQL versions (8.0.x prior to 8.0.19, or 5.7.x). It is important to understand this aspect of InnoDB in order to tune it correctly. This post is a bit long and complex as it goes very deep into some InnoDB internals.

InnoDB internally handles flush operations in the background to remove dirty pages from the buffer pool. A dirty page is a page that is modified in memory but not yet flushed to disk. This is done to lower the write load and the latency of the transactions. Let’s explore the various sources of flushing inside InnoDB.

Idle Flushing

We already discussed the idle flushing in the previous post …

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Examining MySQL InnoDB Persistent Statistics

A few days ago I wrote about how grossly outdated statistics returned through MySQL’s Information_Schema can be. In that post, Øystein Grøvlen suggested taking a look at mysql.innodb_table_stats and mysql.innodb_index_stats as a better source of information. Let’s do just that!

Let’s start with the good news. Unlike MySQL Data Dictionary Tables (mysql.table_stats, etc),  mysql.innodb_table_stats and mysql.innodb_index_stats can be queried by the user. They also contain a lot of interesting statistics. Before we get to that though, let’s examine where those tables come from in more detail.

As the manual tells us, these tables are storing …

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Using Referential Constraints with Partitioned Tables in InnoDB

One of our support customers approached us with the following problem the other day:

mysql> CREATE TABLE child_table (
`id` int unsigned auto_increment,
`column1` varchar(64) NOT NULL,
parent_id int unsigned NOT NULL,
PRIMARY KEY (`id`),
CONSTRAINT FOREIGN KEY (parent_id) REFERENCES parent_table (id));
ERROR 1215 (HY000): Cannot add foreign key constraint

They could not create a table with an FK relation! So, of course, we asked to see the parent table definition, which was:

CREATE TABLE `parent_table` (
  `id` int unsigned auto_increment, 
  `column1` varchar(64) COLLATE utf8_bin NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  
PARTITION BY HASH (id) 
PARTITIONS 4;

The parent table is partitioned!  This immediately explained the problem; partitioned tables can not be part of an FK relationship, as described (in point 10) here – …

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Contention in MySQL InnoDB: Useful Info From the Semaphores Section

In a high concurrency world, where more and more users->connections->threads are used, contention is a given. But how do we identify the contention point easily?

Different approaches had been discussed previously, like the one using Perf and Flame graphs to track down the function taking way more time than expected. That method is great but how can we do it with what one normally has, like the MySQL Client? Enter: the SEMAPHORES section from the SHOW ENGINE INNODB STATUS command output.

SEMAPHORES

The SEMAPHORES section displays all the metrics related to InnoDB mechanics on waits. This section is your best friend if you have a high concurrency workload. In short, it contains 2 kinds of data: …

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Give Love to Your SSDs – Reduce innodb_io_capacity_max!

The innodb_io_capacity and innodb_io_capacity_max are often misunderstood InnoDB parameters. As consultants, we see, at least every month, people setting this variable based on the top IO write specifications of their storage. Is this a correct choice? Is it an optimal value for performance? What about the SSD/Flash wear leveling?

Innodb_io_capacity 101

Let’s begin with what the manual has to say about innodb_io_capacity:

The innodb_io_capacity variable defines the number of I/O operations per second (IOPS) available to InnoDB background tasks, such as flushing pages from the buffer pool and merging data from the change buffer.

What does this mean exactly? …

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Which Indexes are Cached? Discover with PMM.

One of the great things about working at Percona is the constant innovation that occurs as a result of a deep level of technical expertise. A more recent conversation about the Information Schema table: innodb_cached_indexes led to the desire to produce this information in an easy to digest and useful format. Enter PMM.

Our goal with creating this dashboard was to help bring further insight into how your MySQL database cache is being used. Why is this important? Data is accessed significantly faster when it is cached, so indexes that are cached will allow for an increase in query performance. Until now there has not been an easy way to see which indexes are cached and which are not. We want to take the …

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Experimental Build of MyRocks with Percona Server for MySQL

We have been working on bringing out a build of MyRocks with Percona Server for MySQL.

MyRocks is a RocksDB-based storage engine. You can find more information about MyRocks here.

While there is still a lot of work to do, I want to share an experimental build of Percona Server for MySQL with MyRocks, which you can use to evaluate and test this engine

(WARNING: in NO WAY is this build supposed to be for production usage! Consider this ALPHA quality.)

The tar.gz binaries are available from our …

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New MariaDB Dashboard in Percona Monitoring and Management Metrics Monitor

In honor of the upcoming MariaDB M17 conference in New York City on April 11-12, we have enhanced Percona Monitoring and Management (PMM) Metrics Monitor with a new MariaDB Dashboard and multiple new graphs!

The Percona Monitoring and Management MariaDB Dashboard builds on the efforts of the MariaDB development team to instrument the Aria Storage Engine Status Variables related to Aria Pagecache and Aria Transaction Log activity, the tracking of Index Condition Pushdown (ICP), InnoDB Online DDL when using ALTER TABLE ... ALGORITHM=INPLACE, InnoDB Deadlocks …

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