Currently i don't have allocation size set in my @SequenceGenerator annotation. So the default value is 50
int allocationSize() default 50;
As expected there is gap in ids of the correspoding table.
Now i want to change the allocationSize to 1. Is there any chance of id collision then?
I did some experiments to exactly know what will be happening if suddenly someone change the allocationSize from default one.
Short answer to my question is - Yes there will be duplicacy in Id generation.
Before changing allocation size in my application allocationSize = 50 (default)
when sequence value is 4 in db, hibernate start generating id from 4*5 = 200
DEBUG AbstractSaveEventListener - Generated identifier: 200, using strategy: org.hibernate.id.SequenceHiLoGenerator
Which is expected behavior of Hilo generator with this default allocationSize
Then when i change my allocationSize = 1 and deploy my application again.
Now,
Hilo generator start id generation from currentSequenceVal * allocationSize as it did before, for currentSequenceValue = 5, it will generate id 6, 7, 8 ....
which will eventually lead it to duplicate id generation.
Now the solution is to drop the sequence and create the sequence again with starting value currently used maximum id.
