Re: Autovacuum stuck for hours, blocking queries

On 02/17/2017 11:54 PM, Michael Paquier wrote:
> On Sat, Feb 18, 2017 at 1:32 PM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:
>> Yes it can. Truncate has been rollbackable for a while now.
>
> Per the docs:
> https://www.postgresql.org/docs/9.6/static/sql-truncate.html
> "TRUNCATE is transaction-safe with respect to the data in the tables:
> the truncation will be safely rolled back if the surrounding
> transaction does not commit."
> In short yes a transaction doing a truncate can be rollbacked.
>

I think the part that confuses people into thinking it can not be
rollbacked is this:

"TRUNCATE is not MVCC-safe. After truncation, the table will appear
empty to concurrent transactions, if they are using a snapshot taken
before the truncation occurred. See Section 13.5 for more details."

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com