Re: snapshot too old, configured by time

On Mon, Apr 4, 2016 at 8:38 PM, Peter Geoghegan <pg@heroku.com> wrote:
> On Sun, Apr 3, 2016 at 2:09 PM, Jeff Janes <jeff.janes@gmail.com> wrote:
>> Also, HOT-cleanup should stop the bloat increase once the snapshot
>> crosses the old_snapshot_threshold without even needing to wait until
>> the next autovac runs.
>>
>> Does the code intentionally only work for manual vacuums?  If so, that
>> seems quite surprising.  Or perhaps I am missing something else here.
>
> What proportion of the statements in your simulated workload were
> updates? Per my last mail to this thread, I'm interested in knowing if
> this was a delete heavy workload.

It was pgbench's built in  TPC-B-like, so 3 UPDATE, 1 SELECT, 1 INSERT
per transaction.

So I would say that it is ridiculously update heavy compared to almost
any real-world use patterns.

That is the active workload.  The long-term snapshot holder just does
a sum(abalance) at the repeatable read level in order to force a
snapshot to be taken and held, and then goes idle for a long time.

Cheers,

Jeff