Hervé Letourneur ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=712020%... ) *updated* an issue Hibernate ORM ( https://hibernate.atlassian.net/browse/HHH?atlOrigin=eyJpIjoiYzFlOTEwMDNl... ) / Improvement ( https://hibernate.atlassian.net/browse/HHH-16790?atlOrigin=eyJpIjoiYzFlOT... ) HHH-16790 ( https://hibernate.atlassian.net/browse/HHH-16790?atlOrigin=eyJpIjoiYzFlOT... ) Performance issue when retrieving a large bulk of entity in bidirectionnal association ( https://hibernate.atlassian.net/browse/HHH-16790?atlOrigin=eyJpIjoiYzFlOT... ) Change By: Hervé Letourneur ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=712020%... ) We have migrated from Hibernate 5 to 6. Since this migration, we have noticed a downgrade in performance when lazy loading a collection of entity. I have reproduced the issue with the attached entities. In a postgresql DB, we have 150 000 books and 750 000 pages. When we load all books and then via the association all pages linked to books (FetchType.LAZY and FetchMode.SUBSELECT) : * it takes several minutes with the 6.2.4 version of hibernate * it takes several seconds with the 5.6.15 version of hibernate After some analysis, we have noticed that we stay a lot of a time in {{ListResultsConsumer}}. When we aggregate the entities, it use the {{Results}} class and the addUnique method seem to have difficulties to handle a large bulk of entities to aggregate. It seems to be linked to [https://hibernate.atlassian.net/browse/HHH-15479|https://hibernate.atlass...] Do we need do something wrong in our mapping ? Do we have miss something during migration ? Thanks & Regards ( https://hibernate.atlassian.net/browse/HHH-16790#add-comment?atlOrigin=ey... ) Add Comment ( https://hibernate.atlassian.net/browse/HHH-16790#add-comment?atlOrigin=ey... ) Get Jira notifications on your phone! Download the Jira Cloud app for Android ( https://play.google.com/store/apps/details?id=com.atlassian.android.jira.... ) or iOS ( https://itunes.apple.com/app/apple-store/id1006972087?pt=696495&ct=Em... ) This message was sent by Atlassian Jira (v1001.0.0-SNAPSHOT#100226- sha1:1cc165e )