Horton

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

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Alexander Korotkov <a.korotkov@postgrespro.ru>, Thomas Munro <thomas.munro@enterprisedb.com>, Claudio Freire <klaussfreire@gmail.com>, Anastasia Lubennikova <a.lubennikova@postgrespro.ru>, "Andrey V. Lepikhov" <a.lepikhov@postgrespro.ru>
Date: 2019-03-07T08:40:36Z
Lists: pgsql-hackers 
On Thu, Mar 7, 2019 at 12:37 AM Peter Geoghegan <pg@bowt.ie> wrote:
> When I drew you that picture while we were in Lisbon, I mentioned to
> you that the patch sometimes used a sentinel scantid value that was
> greater than minus infinity, but less than any real scantid. This
> could be used to force an otherwise-equal-to-pivot search to go left
> rather than uselessly going right. I explained this about 30 minutes
> in, when I was drawing you a picture.

I meant the opposite: it could be used to go right, instead of going
left when descending the tree and unnecessarily moving right on the
leaf level.

As I said, moving right on the leaf level (rather than during the
descent) should only happen when it's necessary, such as when there is
a concurrent page split. It shouldn't happen reliably when searching
for the same value, unless there really are matches across multiple
leaf pages, and that's just what we have to do.

-- 
Peter Geoghegan

Commits

  1. Add "split after new tuple" nbtree optimization.

  2. Add nbtree high key "continuescan" optimization.

  3. Allow amcheck to re-find tuples using new search.

  4. Consider secondary factors during nbtree splits.

  5. Make heap TID a tiebreaker nbtree index column.

  6. Refactor nbtree insertion scankeys.

  7. Redesign the partition dependency mechanism.

  8. Avoid unnecessary palloc overhead in _bt_first(). The temporary