Re: WIP: pre-upgrade page reservation

Heikki Linnakangas napsal(a):
> Zdenek Kotala wrote:
>> Heikki Linnakangas napsal(a):
>>> Zdenek Kotala wrote:
>>>> BTree space reservation is more complicated.
>>>
>>> Do you need to pre-reserve the space for b-tree? I think you can just
>>> split it at upgrade, in the new version. The problem with doing that
>>> for heaps is that to move a heap tuple you need to update the index
>>> pointers, but for indexes there's no such restriction.
>>
>> The problem is that I need to know parent and modify parent as well.
>> But you don't know what is your parent node. You need to know root and
>> go from root.
>> It is why I think that it is not doable online.
>
> Oh, you're planning to walk the B-tree in index order, not physical
> order, so that you always have the stack for inserting the parents?

Yes, it was a idea.

> You
> don't necessarily need the stack, if you're not worried about
> performance. _bt_insert_parent will scan the next level up to find the
> parent in that case. That's slow, but so is walking the B-tree, and I'd
> expect it to be rare that you need to split b-tree pages at upgrade anyway.

Cool. I overlooked it.

> (I still think you're distracted, BTW. There's zero evidence that we'll
> need any of this for the 8.4->8.5 upgrade. And if we do, we don't know
> for sure that this will solve the problem, whatever the problem is.)

We made a decision in a previous thread that we need space reservation when we
want to have CRC field in page header to prevent space expansion problem in page
conversion during upgrade. I think that currently we know what is necessary for
8.2->8.3/4 upgrade. What problems we can expect. We don't know if these kind of
changes happen in future or not. We know only about CRC at this moment. But I
supposed to prepare PostgreSQL to deal with all this issues. I'm not much happy
with idea to backport a lot of code to older version.

IIRC, we don't plan to backport space reservation back into 8.2, because ...
Why it should be accepted for 8.4 when 8.5 will be released?

Maybe I miss something or maybe I have lost in mailing thread and opinions ...

Zdenek