Horton

Re: Optimizing nbtree ScalarArrayOp execution, allowing multi-column ordered scans, skip scan

Peter Geoghegan <pg@bowt.ie>

View thread
From: Peter Geoghegan <pg@bowt.ie>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Jeff Davis <pgsql@j-davis.com>, benoit <benoit@hopsandfork.com>, Alexander Korotkov <aekorotkov@gmail.com>
Date: 2024-04-08T01:36:17Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Move nbtree preprocessing into new .c file.

  2. Fix nbtree lookahead overflow bug.

  3. Remove unneeded nbtree array preprocessing assert.

  4. Don't try to fix eliminated nbtree array scan keys.

  5. Remove redundant nbtree preprocessing assertions.

  6. Avoid extra lookups with nbtree array inequalities.

  7. Enhance nbtree ScalarArrayOp execution.

  8. Improvements and fixes for e0b1ee17dc

  9. Skip checking of scan keys required for directional scan in B-tree

  10. Fix btmarkpos/btrestrpos array key wraparound bug.

  11. Add nbtree high key "continuescan" optimization.

  12. Consider secondary factors during nbtree splits.

  13. Make heap TID a tiebreaker nbtree index column.

  14. Fix planning of btree index scans using ScalarArrayOpExpr quals.

  15. Fix btree stop-at-nulls logic properly.

  16. Teach btree to handle ScalarArrayOpExpr quals natively.

On Sun, Apr 7, 2024 at 9:25 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Perhaps this'd help:
>
> -                        Assert(xform[j].ikey == array->scan_key);
> +                        Assert(array && xform[j].ikey == array->scan_key);
>
> If that doesn't silence it, I'd be prepared to just dismiss the
> warning.

The assertions in question are arguably redundant. There are very
similar assertions just a little earlier on, as we initially set up
the array stuff (right before _bt_compare_scankey_args is called).
I'll just remove the "Assert(xform[j].ikey == array->scan_key)"
assertion that Coverity doesn't like, in addition to the
"Assert(!array || array->scan_key == i)" assertion, on the grounds
that they're redundant.

> Some work in the comment to explain why we must have an array here
> wouldn't be out of place either, perhaps.

There is a comment block about this right above the assertion in question:

/*
 * Both scan keys might have arrays, in which case we'll
 * arbitrarily pass only one of the arrays.  That won't
 * matter, since _bt_compare_scankey_args is aware that two
 * SEARCHARRAY scan keys mean that _bt_preprocess_array_keys
 * failed to eliminate redundant arrays through array merging.
 * _bt_compare_scankey_args just returns false when it sees
 * this; it won't even try to examine either array.
 */

Do you think it needs more work?

-- 
Peter Geoghegan