Re: Making all nbtree entries unique by having heap TIDs participate in comparisons

On Sat, Mar 16, 2019 at 2:01 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
>
> On Sat, Mar 16, 2019 at 1:47 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> > I agree that it's always true that the high key is also in the parent,
> > and we could cross-check that within the child. Actually, I should
> > probably figure out a way of arranging for the Bloom filter used
> > within bt_relocate_from_root() (which has been around since PG v11) to
> > include the key itself when fingerprinting. That would probably
> > necessitate that we don't truncate "negative infinity" items (it was
> > actually that way about 18 years ago), just for the benefit of
> > verification.
>
> Clarification: You'd fingerprint an entire pivot tuple -- key, block
> number, everything. Then, you'd probe the Bloom filter for the high
> key one level down, with the downlink block in the high key set to
> point to the current sibling on the same level (the child level). As I
> said, I think that the only reason that that cannot be done at present
> is because of the micro-optimization of truncating the first item on
> the right page to zero attributes during an internal page split. (We
> can retain the key without getting rid of the hard-coded logic for
> negative infinity within _bt_compare()).
>
> bt_relocate_from_root() already has smarts around interrupted page
> splits (with the incomplete split bit set).

Clarification to my clarification: I meant
bt_downlink_missing_check(), not bt_relocate_from_root(). The former
really has been around since v11, unlike the latter, which is part of
this new amcheck patch we're discussing.

--
Peter Geoghegan