Re: COPY FREEZE and PD_ALL_VISIBLE

On Fri, Oct 23, 2015 at 6:29 AM, Simon Riggs <simon@2ndquadrant.com> wrote:

> On 21 October 2015 at 13:31, Jeff Janes <jeff.janes@gmail.com> wrote:
>
> Index-only scans will visit the heap for each tuple until the first VACUUM
>> is done.
>>
>> The first vacuum will read the entire table, but not need to write it
>> anymore.  And will create the _vm file.
>>
>> I think we really want to create _vm file as well as set PD_ALL_VISIBLE,
>> but I don't know the best way to do that.  Set a flag somewhere and then
>> create it in bulk at the end of the transaction?  Set it bit by bit as the
>> pages are extended and initialized?
>>
>
> Easy enough to do it at the end of the COPY FREEZE in one step.
>

Here, we might want to consider that setting bit in visibility map
will generate WAL log whereas Copy Freeze otherwise skip WAL
when wal_level is less than archive.  This can lead to extra disk
writes which can slow down Copy Freeze, but OTOH that might
be acceptable.


With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com