Re: Vacuum not deleting tuples when lockless

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> =?UTF-8?q?Mart=C3=ADn_Fern=C3=A1ndez?= <fmartin91(at)gmail(dot)com> writes:
>
>> We are experiencing some `vacuum` issues with a given table
>> (potentially more). When a manual vacuum runs on the given table it
>> seems that the `vacuum` process is not doing the expected cleanup.
>
>> DETAIL:  113257 dead row versions cannot be removed yet.
>
> Locks don't really have anything to do with that: what does matter is
> how old is the oldest open transaction, because that determines the
> "event horizon" that dead row versions have to fall below before they
> can be removed. That oldest transaction might not be holding any locks
> at the moment, but it doesn't matter, because in principle it could ask
> to read this table later --- and it should see the table's contents as
> of its snapshot.
>
> Serializable transactions are worse than repeatable-read transactions
> for this purpose, because the former will keep a snapshot as of their
> start time.
>
> As Jerry mentioned, replication slots can also act like open transactions
> for this purpose, though I don't recall how much of that behavior is
> present in 9.2.x.

Oops, didn't notice OP was on 9.2! Presume none, since I don't think we
got rep slots till 9.4 :-)

>
> regards, tom lane
>
>

--
Jerry Sievers
Postgres DBA/Development Consulting
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