In the just-released MySQL 8.0.14 I added a feature called LATERAL derived tables.
The manual describes the syntax and has examples of how the feature can be used to find greatest values in tables. In the present post I’m going to consider a different problem solved by LATERAL: let’s say that we have a bunch of nodes, and want to make a “random graph”, by connecting every node to other nodes.…
A query plan uses loose index scan if “Using index for group-by” appears in the “Extra” column of the EXPLAIN output. In some plans though, “Using index for group-by (scanning)” appears. What does “(scanning)” mean and how is it different from the regular loose index scan?…
The Write Ahead Log (WAL) is one of the most important components of a database. All the changes to data files are logged in the WAL (called the redo log in InnoDB). This allows to postpone the moment when the modified pages are flushed to disk, still protecting from data losses.…
As of MySQL 8.0.3, you now have the ability to create histogram statistics in order to provide more statistics to the optimizer. In this blog post, we will have a look at how you can create histogram statistics, and we will explain when it might be useful to have histogram statistics.…
MySQL 8.0 introduces Common Table Expressions (CTE). My colleague Guilhem has written several blog posts on how to use CTEs , and you can also read about it in the MySQL 8.0 Reference Manual. In this blog post, I will focus on how using a CTE instead of a view or a derived table can improve performance.…
[Update of April 2017: the features discussed here are now also available in the official release 8.0.1 of MySQL. And this series of posts has been continued, here.]
Here is the third in a series of posts about CTEs, a new feature of MySQL 8.0, available in this Labs release.…
Starting with the 8.0 optimizer labs release the MySQL server now supports descending indexes. As I will detail in this post, this new feature can be used to eliminate the need for sorting results, and lead to performance improvements in a number of queries.…
One of the things we have been working on for MySQL 8, is speeding up scans that read multiple records from a table or an index. Such scans benefit from reading the records in batches, so that they don’t get the overhead of latching data pages and navigating in the B-tree for every single record that is read.…
In a previous post I took the new JSON datatype and functions for a test drive, using sample data provided by SF OpenData. Today I will extend that example to include indexing.
MySQL 5.7 introduces a new feature called generated columns.…