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I'm trying to delete in the order of 1M rows from a MySQL InnoDB table, with a schema similar to:

CREATE TABLE `relations` (
  `id` bigint unsigned NOT NULL AUTO_INCREMENT,
  `relation_type_id` int unsigned DEFAULT NULL,
  `asset_id1` int unsigned DEFAULT NULL,
  `asset_id2` int unsigned DEFAULT NULL,
  `active` smallint unsigned NOT NULL,
  `comments` longtext,
  PRIMARY KEY (`id`),
  UNIQUE KEY `relation_type_id` (`relation_type_id`,`asset_id1`,`asset_id2`),
  KEY `asset_id1` (`asset_id1`),
  KEY `asset_id2` (`asset_id2`),
  CONSTRAINT `relation_ibfk_1` FOREIGN KEY (`relation_type_id`) REFERENCES `relation_type` (`id`),
  CONSTRAINT `relation_ibfk_2` FOREIGN KEY (`asset_id1`) REFERENCES `asset` (`id`),
  CONSTRAINT `relation_ibfk_3` FOREIGN KEY (`asset_id2`) REFERENCES `asset` (`id`)

This table has about 250M rows.

I need to delete every record where asset_id1 belongs to a set of about 1M size. I'm using SQLAlchemy in python, SQL queries constructed look like

DELETE FROM relations where asset_id1 IN (a0, a1, ... a1_000_000) 

No assumptions on the ordering, even if I sort the input set, the relation rows id column may have a whole different ordering.

I'm taking 20-30 minutes to do this - am I missing any optimization techniques?

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  • Do it in loops/batches. Queue up the full list of items to delete into a stage/temp table. Then loop through in batches of xxx thousand and do the deletes that way in batches. Even if it takes a while it will not completely block the table during the delete because you are doing it in batches/loops. Can even include a pause in each loop for 1 second or so to help ensure less blocking.
    – Brad
    Apr 3 at 17:17
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    i would create a temporary table and join it to find the wanted rows
    – nbk
    Apr 3 at 17:22
  • Thanks for the suggestions. Sadly, this is in the context of a longer transaction, so no implicit commits can be done, and the script does not have CREATE TEMPORARY TABLE privileges. Sorry for leaving that behind in the original problem statement. Apr 3 at 17:35

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