Michael Paquier <michael.paquier@gmail.com> writes:
> On Thu, Sep 21, 2017 at 8:18 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> "Bossart, Nathan" <bossartn@amazon.com> writes:
>>> I agree that the patch might be simpler without this, but the user-visible
>>> behavior is the reason I had included it. In short, my goal was to avoid
>>> errors halfway through a long-running VACUUM statement because the user
>>> misspelled a relation/column name or the relation/column was dropped.
>> I don't particularly buy that argument, because it's not the case that
>> the preceding processing was wasted when that happens. We've done and
>> committed the vacuuming work for the earlier relations.
> I think that the problem can be seen differently though: the next
> relations on the list would not be processed as well. For example in
> parallel of a manual VACUUM triggered by a cron job, say that a rogue
> admin removes a column for a relation to be VACUUM-ed. The relations
> processed before the relation redefined would have been vacuumed and
> the transaction doing the vacuum committed, but the ones listed after
> would not have been updated in this nightly VACUUM.
Um ... so? With Nathan's proposed behavior, there are two cases depending
on just when the unexpected schema change happens:
1. *None* of the work gets done.
2. The work before the troublesome relation gets done, and the work after
doesn't.
I think it'll be much easier to understand if the behavior is always (2).
And I don't see any particular advantage to (1) anyway, especially not
for an unattended vacuum script.
Keep in mind that there were not-entirely-unjustified complaints upthread
about whether we needed to add any complexity here at all. I'd just as
soon keep the added complexity to a minimum, especially when it's in
service of behaviors that are not clearly improvements.
regards, tom lane
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