Horton

Re: WIP: Covering + unique indexes.

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2018-03-29T23:33:37Z
Lists: pgsql-hackers 
On Wed, Mar 28, 2018 at 7:59 AM, Anastasia Lubennikova
<a.lubennikova@postgrespro.ru> wrote:
> Here is the new version of the patch set.
> All patches are rebased to apply without conflicts.
>
> Besides, they contain following fixes:
> - pg_dump bug is fixed
> - index_truncate_tuple() now has 3rd argument new_indnatts.
> - new tests for amcheck, dblink and subscription/t/001_rep_changes.pl
> - info about opclass implementors and included columns is now in sgml doc

This only changes the arguments given to index_truncate_tuple(), which
is a superficial change. It does not actually change anything about
the on-disk representation, which is what I sought. Why is that a
problem? I don't think it's very complicated.

The patch needs a rebase, as Erik mentioned:

1 out of 19 hunks FAILED -- saving rejects to file
src/backend/utils/cache/relcache.c.rej
(Stripping trailing CRs from patch; use --binary to disable.)

I also noticed that you still haven't done anything differently with
this code in _bt_checksplitloc(), which I mentioned in April of last
year:

    /* Account for all the old tuples */
    leftfree = state->leftspace - olddataitemstoleft;
    rightfree = state->rightspace -
        (state->olddataitemstotal - olddataitemstoleft);

    /*
     * The first item on the right page becomes the high key of the left page;
     * therefore it counts against left space as well as right space.
     */
    leftfree -= firstrightitemsz;

    /* account for the new item */
    if (newitemonleft)
        leftfree -= (int) state->newitemsz;
    else
        rightfree -= (int) state->newitemsz;

With an extreme enough case, this could result in a failure to find a
split point. Or at least, if that isn't true then it's not clear why,
and I think it needs to be explained.

-- 
Peter Geoghegan

Commits

  1. Adjust INCLUDE index truncation comments and code.

  2. Add commentary explaining why MaxIndexTuplesPerPage calculation is safe.

  3. Indexes with INCLUDE columns and their support in B-tree

  4. Add amcheck verification of heap relations belonging to btree indexes.

  5. Doc: move info for btree opclass implementors into main documentation.

  6. Doc: mention that you can't PREPARE TRANSACTION after NOTIFY.

  7. Remove dedicated B-tree root-split record types.

  8. Restructure index access method API to hide most of it at the C level.

  9. Split _bt_insertonpg to two functions.

  10. Major overhaul of btree index code. Eliminate special BTP_CHAIN logic for