Fixing holes/gaps in numbers generated by Postgres

问题:

I have a postgres database that uses sequences extensively to generate primary keys of tables. After a lot of usage of this database i.e. Adding/Update/Delete operation the columns that uses sequences for primary keys now have a lot holes/gaps in them and the sequence value itself is very high.

My question is: Are there any ways in which we can fix these gaps in Primary Keys? which should inturn bring down the max value of the number in that columns and then reset the sequence?

Note: A lot of these columns are also referenced by other columns as ForeignKeys.

回答1:

If you feel the need to fill gaps in auto-generated Posgresql sequence numbers, I have the feeling you need another field in your table, like some kind of "number" you increment programmatically, either in your code, or in a trigger.

回答2:

It is possible to solve this problem, but is expensive for the database to do (especially IO) and is guaranteed to reoccur. I would not worry about this problem. If you get close to 4B, upgrade your primary and foreign keys to BIGSERIAL and BIGINT. If you're getting close to 2^64... well... I'd be interested in hearing more about your application. :~]

回答3:

Postgres allows you to update PKs, although a lot of people think it's bad practice. So you could lock the table, and UPDATE. (You can make an oldkey, newkey table all sorts of ways, e.g., window function.) All the FK relationships have to be marked to cascade. Then you can reset the currval of the id sequence.

Personally, I would just use a BIGSERIAL. If you have so many updates and deletes that you may run out even so, maybe there is some composite PK based on (say) a timestamp and id that would help you.