Re: [PATCHES] TRUNCATE TABLE with IDENTITY - Mailing list pgsql-hackers

Alvaro Herrera <alvherre@commandprompt.com> writes:
> Tom Lane wrote:
>> 2. I had first dismissed Neil's idea of transactional sequence updates
>> as impossible, but on second look it could be done.  Suppose RESTART
>> IDENTITY does this for each sequence;
>>
>> * obtain AccessExclusiveLock;
>> * assign a new relfilenode;
>> * insert a sequence row with all parameters copied except
>> last_value copies start_value;
>> * hold AccessExclusiveLock till commit.

> Hmm, this kills the idea of moving sequence data to a single
> non-transactional catalog :-(

Well, there are a number of holes in our ideas of how to do that anyway.
But offhand I don't see why we couldn't distinguish regular heap_update
from update_in_place on single rows within a catalog.

            regards, tom lane