Our website crashing with this error.

Warning: mysqli_real_connect(): (42000/1226): User 'USER' has exceeded the 'max_user_connections' resource (current value: 25) in /home/PATH/wp-includes/wp-db.php on line 1626

20515788 DATABASE localhost USER Query 8570 Waiting for table metadata lock ALTER TABLE wp_wpdatatables_columns MODIFY COLUMN column_type 

These show up in SQL processlist as:

| 21094556 | DATABASE | localhost | USER| Query | 4890 | Waiting for table level lock | UPDATE `wp_wpdatatables_columns` SET `column_type` = 'masterdetail' WHERE `orig_header` = 'master | 0.000 |

Please advise why this is happening - we are not working on wpdatatables when this occurs and crashes site.

Whatever this is seems to relate to masterdetail addon. When the processlist was cleared allowing us back into website, all 12 databases had master detail functionality turned on in admin, but it was not present on frontend. When we toggled the masterdetail status, it came back.

No, this is not resolved. It still happens.
No, we did not make changes to the tables before the problem.
Please understand we are not using wpdatatables when this problem occurs.

We have much more detail on this now however;

We have further narrowed the trigger

• these spam queries regards masterdetail occur when a WooCommerce product is updated. 
• It does not occur when a page or post is updated.

6 queries are created, for each product update. 

These queries time out. That means if enough products are updated in a short period ()only around 4 or so), the WordPress database user hits max_user_connections.

15 seconds after updating one WooCommerce product, here are the queries on the server:

Here is my processlist query, we expect that:

    -> | 22522955 | lxuqyepr_bafhs | localhost | lxuqyepr_bafhs | Query   |    0 | Init                            | show full processlist                                                                                                                                                               |    0.000 |

Then masterdetail related queries, one like this:

    -> | 22524175 | lxuqyepr_bafhs | localhost | lxuqyepr_bafhs | Query   |   15 | Waiting for table level lock    | UPDATE `hdgtf_wpdatatables_columns` SET `column_type` = 'masterdetail' WHERE `orig_header` = 'masterdetail'                                                                         |    0.000 |

Then 5 like this:

    -> | 22524176 | lxuqyepr_bafhs | localhost | lxuqyepr_bafhs | Query   |   15 | Waiting for table metadata lock | ALTER TABLE hdgtf_wpdatatables_columns MODIFY COLUMN column_type ENUM('autodetect','string','int','float','date','link','email','image','formula','datetime','time','masterdetail') |    0.000 |
    -> | 22524177 | lxuqyepr_bafhs | localhost | lxuqyepr_bafhs | Query   |   15 | Waiting for table metadata lock | ALTER TABLE hdgtf_wpdatatables_columns MODIFY COLUMN column_type ENUM('autodetect','string','int','float','date','link','email','image','formula','datetime','time','masterdetail') |    0.000 |
    -> | 22524178 | lxuqyepr_bafhs | localhost | lxuqyepr_bafhs | Query   |   15 | Waiting for table metadata lock | ALTER TABLE hdgtf_wpdatatables_columns MODIFY COLUMN column_type ENUM('autodetect','string','int','float','date','link','email','image','formula','datetime','time','masterdetail') |    0.000 |
    -> | 22524179 | lxuqyepr_bafhs | localhost | lxuqyepr_bafhs | Query   |   15 | Waiting for table metadata lock | ALTER TABLE hdgtf_wpdatatables_columns MODIFY COLUMN column_type ENUM('autodetect','string','int','float','date','link','email','image','formula','datetime','time','masterdetail') |    0.000 |
    -> | 22524291 | lxuqyepr_bafhs | localhost | lxuqyepr_bafhs | Query   |    0 | Waiting for table metadata lock | ALTER TABLE hdgtf_wpdatatables_columns MODIFY COLUMN column_type ENUM('autodetect','string','int','float','date','link','email','image','formula','datetime','time','masterdetail') |    0.000 |

Clearly these queries shouldnt be happening!