I started an application with Hibernate 3.2 and PostgreSQL 8.4. I have some byte[] fields that were mapped as @Basic (= PG bytea) and others that got mapped as @Lob (=PG Large Object). Why the inconsistency? Because I was a Hibernate noob.
Now, those fields are max 4 Kb (but average is 2-3 kb). The PostgreSQL documentation mentioned that the LOs are good when the fields are big, but I didn't see what 'big' meant.
I have upgraded to PostgreSQL 9.0 with Hibernate 3.6 and I was stuck to change the annotation to @Type(type="org.hibernate.type.PrimitiveByteArrayBlobType"). This bug has brought forward a potential compatibility issue, and I eventually found out that Large Objects are a pain to deal with, compared to a normal field.
So I am thinking of changing all of it to bytea. But I am concerned that bytea fields are encoded in Hex, so there is some overhead in encoding and decoding, and this would hurt the performance.
Are there good benchmarks about the performance of both of these? Anybody has made the switch and saw a difference?
Basically there are cases where each makes sense. bytea is simpler and generally preferred. The client libs give you the decoding so that's not an issue.
However LOBs have some neat features, such as an ability to seek within them and treat the LOB as a byte stream instead of a byte array.
"Big" means "Big enough you don't want to send it to the client all at once." Technically bytea is limited to 1GB compressed and a lob is limited to 2GB compressed, but really you hit the other limit first anyway. If it's big enough you don't want it directly in your result set and you don';t want to send it to the client all at once, use a LOB.