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When order of appearance of indexes matters in MySQL

Sometimes MySQL surprises you in ways you would have never imagined.

Would you think that the order in which the indexes appear in a table matters?
It does. Mind you, not the order of the columns - the order of the indexes.
MySQL optimizer can, in specific circumstances, take different paths, sometimes with nefarious effects.


Please consider the following table:

CREATE TABLE `mypartitionedtable ` (
  `HASH_ID` char(64) NOT NULL,
  `RAW_DATA` mediumblob NOT NULL,
  `EXPIRE_DATE` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  KEY `EXPIRE_DATE_IX` (`EXPIRE_DATE`),
  KEY `HASH_ID_IX` (`HASH_ID`)
) ENGINE=TokuDB DEFAULT CHARSET=latin1 ROW_FORMAT=TOKUDB_UNCOMPRESSED
/*!50100 PARTITION BY RANGE (UNIX_TIMESTAMP(EXPIRE_DATE))
(PARTITION p2005 VALUES LESS THAN (1487847600) ENGINE = …

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MySQL Group Replication: about ack from majority

The documentation states that “For a transaction to commit, the majority of the group have to agree on the order of a given transaction in the global sequence of transactions.

This means that as soon as the majority of nodes member of the group ack the writeset reception, certification can start. So, as a picture is worth a 1000 words, this is what it looks like if we take the illustrations from my previous post:

a group of 3 members

zoom in transaction deliverthe writer also acksmajority is reached, the system agreed on the orderack of the remaining node will come too but the order has been already decided

 

certification can startthe process then continues as usual

So theoretically, having 2 nodes in one DC and 1 node in another DC shouldn’t be affected …

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Converting comma separated fields to MySQL JSON – a case study

This post is a case study of a job I had to do in a legacy application, it doesn’t mean it will apply to you, but it might.

This is a table of contents:

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Webinar Thursday, February 23, 2017: Troubleshooting MySQL Access Privileges Issues

Please join Sveta Smirnova, Percona’s Principal Technical Services Engineer, as she presents Troubleshooting MySQL Access Privileges Issues on
February 23, 2017 at 11:00 am PST / 2:00 pm EST (UTC-8).

Do you have registered users who can’t connect to the MySQL server? Strangers modifying data to which they shouldn’t have access?

MySQL supports a rich set of user privilege options and allows you to fine tune access to every object in the server. The latest versions support authentication plugins that help to create more access patterns.

However, finding errors in …

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Percona XtraBackup 2.4.6 is Now Available

Percona announces the GA release of Percona XtraBackup 2.4.6 on February 22, 2017. You can download it from our download site and apt and yum repositories.

Percona XtraBackup enables MySQL backups without blocking user queries, making it ideal for companies with large data sets and mission-critical applications that cannot tolerate long periods of downtime. Offered free as an open source solution, Percona …

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Percona XtraBackup 2.3.7 is Now Available

Percona announces the release of Percona XtraBackup 2.3.7 on February 22, 2017. Downloads are available from our download site or Percona Software Repositories.

Percona XtraBackup enables MySQL backups without blocking user queries, making it ideal for companies with large data sets and mission-critical applications that cannot tolerate long periods of downtime. Offered free as an open source solution, Percona XtraBackup drives down backup costs while providing unique features for MySQL backups.

This release is the …

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MySQL Connector/NET 6.10.1 beta has been released

MySQL Connector/Net 6.10.1 beta is the second release which supports Scaffold-DbContext, that enables the creation of corresponding model classes from an existing database that are compatible with Entity Framework (EF) Core 1.1.

To download MySQL Connector/Net 6.10.1 beta, see the “Development Releases” tab at http://dev.mysql.com/downloads/connector/net/

Known limitations of this release

  • The output classes cannot exist prior to using the EF Core database first feature.
  • The target database must have a table with a primary key.
  • The target database cannot contain one or more views.
  • The JSON data exchange format is not supported by the EF Core database first feature.
  • No error message is provided when a table given as input does not exist in the database and a model context is …
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Log Buffer #505: A Carnival of the Vanities for DBAs

This Log Buffer Edition searches through various blogs of Oracle, SQL Server and MySQL and picks a few contemporary ones.

Oracle:

Comma separated search and search with check-boxes in Oracle APEX

Once you have defined your users for your Express Cloud Service, all users with the role of Database Developer or higher can access the database Service Console.

Big Data Lite 4.7.0 is now available on OTN!

Install and configure Oracle HTTP Server Standalone

Can I …

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Codeigniter 3 CRUDCreate Read Update and Delete using JQuery Ajax Bootstrap Models and MySQL

Today i am going to share with you how to create CRUD Application with pagination using JQuery Ajax in Codeigniter 3CRUD is a basic step of any Core Language or framework CRUD stand for Create Read Update and Delete So in this post we will learn insert update delete in codeigniter using jquery

Codeigniter 3 CRUDCreate Read Update and Delete using JQuery Ajax Bootstrap Models and MySQL

Today i am going to share with you how to create CRUD Application with pagination using JQuery Ajax in Codeigniter 3CRUD is a basic step of any Core Language or framework CRUD stand for Create Read Update and Delete So in this post we will learn insert update delete in codeigniter using jquery

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