| parent | RECORD | S,REC_NOT_GAP | 3 | GRANTED | | parent | RECORD | X,REC_NOT_GAP | 1, 1 | GRANTED | If we look at the trigger in the where section This makes reads consistent and therefore makes the replication between servers consistent. When we run the same query twice, we get the same result, regardless other session modifications on that table. What does a gap lock mean? A gap lock is a lock on a gap between index records, or a lock on the gap before the first or after the last index record. We want to read the records that are not touched by the second session. | parent | RECORD | S | supremum pseudo-record | GRANTED | | id | parent_name | child_id | child_name | Mysql> select * from parent where id1 for share Session one locks two rows in the parent table, one of which is a gap lock. | parent | RECORD | X,GAP | 2, 2 | GRANTED | | parent | RECORD | X,REC_NOT_GAP | 1 | GRANTED | | child | RECORD | X,REC_NOT_GAP | 1 | GRANTED | ![]() | parent | RECORD | X,REC_NOT_GAP | 1 | WAITING | | object_name | lock_type | lock_mode | lock_data | lock_status | Mysql> SELECT object_name, lock_type, lock_mode, lock_data, lock_status FROM performance_schema.data_locks Mysql> update parent set parent_name='parent2' where id=1 ![]() We’re gonna add a column to the parent table. Please check this article in order to prepare your setup. So now that we found a valid case for using triggers, let’s see what we need to be careful when using them. And in the same time we don’t want to work on the monolith to add more code which would support this migration, so the obvious choice would be to use database triggers. Of course in order to do this we need to synchronise the data. We want to keep the monolith working but in the same time prepare the new services so that we can do a canary release at some point. So, we’re not going with a bing bang approach but with incremental changes. One case for this would be refactoring your monolith to microservices and part of that is this database migration. Or you could break one table in multiple tables, in order to separate domain concepts. Let’s say that part of the migration you create new separate schema which you plan to use it for the new version. But if you plan to do a database migration you may find them handy. Who uses triggers you may wonder? That’s a valid question. ![]() We look for both the 2 lock struct(s) and the ACTIVE 21 sec messages.We are in 2019. MySQL thread id 217, OS thread handle 0x2aef097700, query id 1177 1.3.5.7 mpsp cleaning up In our TRANSACTIONS section we also see the following: -TRANSACTION 644793773, ACTIVE 21 secĢ lock struct(s), heap size 360, 1 row lock(s) This worked on AWS MySQL RDS as well as local MySQL. To kill it you need to execute by using the "thread id #" specified - in this case: kill 12505095 MySQL thread id 12505095, query id 909492789 129.54įor us it was the # lock struct(s) that indicated a stuck lock. In your output the relevant problem seems to be: 3 lock struct(s), heap size 1248, 2 row lock(s) The relevant section is in the TRANSACTIONS section. This spits out a crap-ton of information. We found the locks by combing trough the output from: show engine innodb status We were seeing Java hibernate issues causing stuck locks. Using 'show engine innodb status' I see that wordpress has two deadlocks. RECORD LOCKS space id 4951009 page no 4 n bits 384 index `option_name` of table `wordpress_work`.`wp_options` trx id 9FBA0995 lock_mode X waiting *** (2) WAITING FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 4951009 page no 4 n bits 384 index `option_name` of table `wordpress_work`.`wp_options` trx id 9FBA0995 lock_mode X locks rec but not gap TRANSACTION 9FBA0995, ACTIVE 0 sec, process no 14207, OS thread id 1230031168 starting index readģ lock struct(s), heap size 1248, 2 row lock(s) RECORD LOCKS space id 4951009 page no 4 n bits 384 index `option_name` of table `wordpress_work`.`wp_options` trx id 9FBA099E lock_mode X waiting *** (1) WAITING FOR THIS LOCK TO BE GRANTED: MySQL thread id 12505112, query id 909492800 129.54 wordpress_user updatingĭELETE FROM wp_options WHERE option_name = ''_site_transient_timeout_theme_roots'' LOCK WAIT 2 lock struct(s), heap size 376, 1 row lock(s) TRANSACTION 9FBA099E, ACTIVE 0 sec, process no 14207, OS thread id 1228433728 starting index read I can see thread ids, query ids, etc but nothing that I can use to stop either job.ĮDIT: Here's the (relevant?) portion of the status:. I'd like to clear these up but I don't see an active process for either of these cmds (IE something to 'kill' and hopefully force a rollback).
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