On Jul 10, 2007, at 3:09 PM, Tom Lane wrote:
"Harpreet Dhaliwal" <harpreet.dhaliwal01@xxxxxxxxx> 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?
