> > "Harpreet Dhaliwal" < harpreet.dhaliwal01@gmail.com> writes: >> Transaction 1 started, saw max(dig_id) = 30 and inserted new >> dig_id=31. >> Now the time when Transaction 2 started and read max(dig_id) it >> was still 30 >> and by the time it tried to insert 31, 31 was already inserted by >> Transaction 1 and hence the unique key constraint error. > > This is exactly why you're recommended to use sequences (ie serial > columns) for generating IDs. Taking max()+1 does not work, unless > you're willing to lock the whole table and throw away vast amounts of > concurrency.
I wonder how SQL server is handling this? Are they locking the table? I realize it's off-topic, but I'm still curious.
Sequences are your friend. they come in INT and BIGINT flavors, but BIGINT is a lot of rows.
Can set set Sequences to automatically rollover back to zero?