Re: Freeze avoidance of very large table.

On Mon, Jul 13, 2015 at 9:03 PM, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com> wrote:
> On Mon, Jul 13, 2015 at 7:46 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> On Mon, Jul 13, 2015 at 3:39 PM, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com>
>> wrote:
>>>
>>> On Tue, Jul 7, 2015 at 9:07 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>>> > On 6 July 2015 at 17:28, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>>> >
>>> >> I think we need something for pg_upgrade to rewrite existing VMs.
>>> >> Otherwise a large read only database would suddenly require a massive
>>> >> revacuum after upgrade, which seems bad. That can wait for now until we
>>> >> all
>>> >> agree this patch is sound.
>>> >
>>> >
>>> > Since we need to rewrite the "vm" map, I think we should call the new
>>> > map
>>> > "vfm"
>>> >
>>> > That way we will be able to easily check whether the rewrite has been
>>> > conducted on all relations.
>>> >
>>> > Since the maps are just bits there is no other way to tell that a map
>>> > has
>>> > been rewritten
>>>
>>> To avoid revacuum after upgrade, you meant that we need to rewrite
>>> each bit of vm to corresponding bits of vfm, if it's from
>>> not-supporting vfm version(i.g., 9.5 or earlier ). right?
>>> If so, we will need to do whole scanning table, which is expensive as
>>> well.
>>> Clearing vm and do revacuum would be nice, rather than doing in
>>> upgrading, I think.
>>>
>>
>> How will you ensure to have revacuum for all the tables after
>> upgrading?
>
> We use script file which are generated by pg_upgrade.

I haven't followed this thread closely, but I am sure you recall that
vacuumdb has a parallel mode.
--
Michael