Revert MySQL default version back to 5.7.26

Author: AMecea

Changelog.md

@@ -49,7 +49,6 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
    output Stackdrive compatible format.
  * Decrease `MASTER_CONNECT_RETRY` interval from 10 to 1 second.
  * Deprecate `TmpfsSize` because can be handled using `ExtraVolumes` and `ExtraMySQLVolumesMounts`.
- * Set default mysql to `5.7.29`.
  * Update cron documentation
  * Set InnoDB buffer parameter: `innodb_buffer_pool_instances` to `min(resources.limit.cpu,
    floor(innodb_buffer_pool_size/1G))` (see #502)

pkg/util/constants/constants.go

@@ -78,13 +78,15 @@ const (
 
 var (
 	// MySQLDefaultVersion is the version for mysql that should be used
-	MySQLDefaultVersion = semver.MustParse("5.7.29")
+	MySQLDefaultVersion = semver.MustParse("5.7.26")
 	// MySQLTagsToSemVer maps simple version to semver versions
 	MySQLTagsToSemVer = map[string]string{
-		"5.7": "5.7.29",
+		"5.7": "5.7.26",
 	}
 	// MysqlImageVersions is a map of supported mysql version and their image
 	MysqlImageVersions = map[string]string{
+		// This version of mysql has a bug and doesn't work with the operator,
+		// see: https://github.com/presslabs/mysql-operator/issues/509
 		"5.7.29": "percona@sha256:d801123bbfaf750924f993f5c59189d144a93feb928b8aef95e541dd61c62881",
 		// Percona:5.7.26 CentOS based image
 		"5.7.26": "percona@sha256:713c1817615b333b17d0fbd252b0ccc53c48a665d4cfcb42178167435a957322",