Horton

Re: WIP: Covering + unique indexes.

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Alexander Korotkov <a.korotkov@postgrespro.ru>
Cc: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2018-03-31T05:46:10Z
Lists: pgsql-hackers 
On Fri, Mar 30, 2018 at 10:39 PM, Peter Geoghegan <pg@bowt.ie> wrote:
> It's safe, although I admit that that's a bit hard to see.
> Specifically, look at this code in _bt_insert_parent():
>
>         /*
>          * Find the parent buffer and get the parent page.
>          *
>          * Oops - if we were moved right then we need to change stack item! We
>          * want to find parent pointing to where we are, right ?    - vadim
>          * 05/27/97
>          */
>         ItemPointerSet(&(stack->bts_btentry.t_tid), bknum, P_HIKEY);
>         pbuf = _bt_getstackbuf(rel, stack, BT_WRITE);
>
> Vadim doesn't seem too sure of why he did it that way. What's clear is
> that the offset on all internal pages is always P_HIKEY (that is, 1),
> because this is the one and only place where new IndexTuples get
> generated for internal pages. That's unambiguous. So how could
> BTEntrySame() truly need to care about offset? How could there ever be
> an internal page offset that wasn't just P_HIKEY? You can look
> yourself, using pg_hexedit or pageinspect.

Sorry, I meant this code, right before:

        /* form an index tuple that points at the new right page */
        new_item = CopyIndexTuple(ritem);
        ItemPointerSet(&(new_item->t_tid), rbknum, P_HIKEY);

-- 
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