公式リポジトリでサポートされている最新バージョンのパッケージをどのように見つけますか？

yum 構成されたリポジトリー（デフォルトでは公式リポジトリーを含む）で利用できるものについて説明します。

$ yum search mariadb
======================================================= N/S matched: mariadb =======================================================
mariadb-bench.x86_64 : MariaDB benchmark scripts and data
mariadb-devel.i686 : Files for development of MariaDB/MySQL applications
mariadb-devel.x86_64 : Files for development of MariaDB/MySQL applications
mariadb-embedded.i686 : MariaDB as an embeddable library
mariadb-embedded.x86_64 : MariaDB as an embeddable library
mariadb-embedded-devel.i686 : Development files for MariaDB as an embeddable library
mariadb-embedded-devel.x86_64 : Development files for MariaDB as an embeddable library
mariadb-libs.i686 : The shared libraries required for MariaDB/MySQL clients
mariadb-libs.x86_64 : The shared libraries required for MariaDB/MySQL clients
mariadb-server.x86_64 : The MariaDB server and related files
mariadb.x86_64 : A community developed branch of MySQL
mariadb-test.x86_64 : The test suite distributed with MariaD

$ yum info mariadb
Available Packages
Name        : mariadb
Arch        : x86_64
Epoch       : 1
Version     : 5.5.65
Release     : 1.el7
Size        : 8.7 M
Repo        : base/7/x86_64
Summary     : A community developed branch of MySQL
URL         : http://mariadb.org
License     : GPLv2 with exceptions and LGPLv2 and BSD
Description : MariaDB is a community developed branch of MySQL.
            : MariaDB is a multi-user, multi-threaded SQL database server.
            : It is a client/server implementation consisting of a server daemon (mysqld)
            : and many different client programs and libraries. The base package
            : contains the standard MariaDB/MySQL client programs and generic MySQL files.

また、使用yum list可能なバージョンとそれらを提供するリポジトリの簡単な要約を取得するために使用することもできます。

Redisは公式のCentOSリポジトリでは利用できませんが、EPELでは利用できます。

$ sudo yum install -y epel-release
[...]

$ yum info redis
Available Packages
Name        : redis
Arch        : x86_64
Version     : 3.2.12
Release     : 2.el7
Size        : 544 k
Repo        : epel/x86_64
Summary     : A persistent key-value database
URL         : http://redis.io
License     : BSD
Description : Redis is an advanced key-value store. It is often referred to as a data
            : structure server since keys can contain strings, hashes, lists, sets and
            : sorted sets.
[...]

特定のパッケージの新しいバージョンの良い情報源はソフトウェアコレクションです。たとえば、MariaDB10.3はそこで利用できます。