I'm getting an error executing batch inserts with a constraint violation exception, which to me makes no sense.

I'm getting a list of users from a table and then looking for entries of those users in an auditing table. If not there, insert them. Because I'm dealing with a lot of users, I batch up the data to be inserted, creating a list of objects and then using *saveAll(list)* to batch them up.

I'm using Spring Boot 2.1.4 and HikariCP 3.3.1. The primary key of the table getting the inserts is the ID field that is auto-generated. So how I could be getting duplicate entry errors is unclear, unless perhaps this is a timing issue.

I'm batching 1000 objects/statements at a time. It works for at least 1 set of 1000 before it barfs. I'm assuming that the "managed flush" error is a side effect of the duplicate entry error.

My entity is:

@Data
@Entity
@Table(name = "event_state", schema = "subscription")
public class EventState

Here is the application.properties file:

spring.output.ansi.enabled=ALWAYS

1. logging
   logging.file=/tmp/activeusers.log

#HikariCP config
subscription.datasource.url=jdbc:mysql://mysqlhost:3306/subscription
subscription.datasource.username=USER
subscription.datasource.password=PASS
subscription.datasource.driverClassName=com.mysql.cj.jdbc.Driver
subscription.datasource.hikari.connection-timeout=60000
subscription.datasource.hikari.maximum-pool-size=6
subscription.datasource.hikari.idle-timeout=300000
subscription.datasource.hikari.max-lifetime=1800000
subscription.datasource.hikari.minimum-idle=6
subscription.datasource.hikari.auto-commit=false
subscription.datasource.hikari.validation-timeout=15000
subscription.datasource.cachePrepStmts=true
subscription.datasource.prepStmtCacheSize=250
subscription.datasource.prepStmtCacheSqlLimit=2048
subscription.datasource.useServerPrepStmts=false
subscription.datasource.useLocalSessionState=true
subscription.datasource.rewriteBatchedStatements=true
subscription.datasource.cacheResultSetMetadata=true
subscription.datasource.cacheServerConfiguration=true
subscription.datasource.elideSetAutoCommits=false
subscription.datasource.maintainTimeStats=false
subscription.datasource.hikari.pool-name=SubscriptionPool

#HikariCP config
activity.datasource.url=jdbc:mysql://mysqlhost:3306/activity
activity.datasource.username=USER
activity.datasource.password=PASS
activity.datasource.driverClassName=com.mysql.cj.jdbc.Driver
activity.datasource.hikari.connection-timeout=60000
activity.datasource.hikari.maximum-pool-size=6
activity.datasource.hikari.idle-timeout=300000
activity.datasource.hikari.max-lifetime=1800000
activity.datasource.hikari.minimum-idle=6
activity.datasource.hikari.auto-commit=true
activity.datasource.hikari.validation-timeout=15000
activity.datasource.cachePrepStmts=true
activity.datasource.prepStmtCacheSize=250
activity.datasource.prepStmtCacheSqlLimit=2048
activity.datasource.useServerPrepStmts=true
activity.datasource.useLocalSessionState=true
activity.datasource.rewriteBatchedStatements=true
activity.datasource.cacheResultSetMetadata=true
activity.datasource.cacheServerConfiguration=true
activity.datasource.elideSetAutoCommits=true
activity.datasource.maintainTimeStats=false
activity.datasource.hikari.pool-name=ActivityPool

spring.jpa.properties.hibernate.jdbc.batch_size=500
spring.jpa.properties.hibernate.order_inserts=true
spring.jpa.properties.hibernate.order_updates=true

I had batch_size set at 1000 originally, then changed it to 100.

UPD 1: tried changing from using *saveAll* to *save* in a loop. Same problem.
UPD 2: tried switching to the MariaDB driver, but had the same problem.

I don't know if there is a config issue with HikariCP or a Hibernate issue or both. The problem is on the subscription DB, and only one thread does the *saveAll*.