Horton

Re: WIP: Covering + unique indexes.

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Teodor Sigaev <teodor@sigaev.ru>
Cc: Alexander Korotkov <a.korotkov@postgrespro.ru>, Anastasia Lubennikova <a.lubennikova@postgrespro.ru>, Thomas Munro <thomas.munro@enterprisedb.com>, Andrey Borodin <x4mmm@yandex-team.ru>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Anastasia Lubennikova <lubennikovaav@gmail.com>
Date: 2018-03-27T22:46:33Z
Lists: pgsql-hackers 
On Tue, Mar 27, 2018 at 10:14 AM, Teodor Sigaev <teodor@sigaev.ru> wrote:
>> b) I don't like an idea to limiting usage of that field if we can do not
>> that. Future usage could use it, for example, for different compression
>> technics or something else.Or even removing t_tid from inner tuples to save
>> 2 bytes in IndexTupleData. Of
>
> course, I remember about aligment, but it could be subject to change too in
> future.

This is contradictory. You seem to be arguing that we need to preserve
on-disk compatibility for an optimization that throws out on-disk
compatibility.

Saving a single byte per internal IndexTuple is not worth it. We could
actually save 2 bytes in *all* nbtree pages, by halving the size of
ItemId for nbtree -- we don't need lp_len, which is redundant, and we
could reclaim one of the status bits too, to get back a full 16 bits.
Also, we could use suffix truncation to save at least one byte in
almost all cases, even with the thinnest possible
single-integer-attribute IndexTuples. What you describe just isn't
going to happen.

-- 
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