pgsql: REPACK CONCURRENTLY: Initialize the range table more honestly

REPACK CONCURRENTLY: Initialize the range table more honestly

We were skipping a bunch of things that are mostly unnecessary for
REPACK. However, one thing that seems would be better to pass closer to
truth, is the updatedCols bitmapset in the range table entry for the
repacked table. Cons up an RTE and install it into the EState.

This only has an effect on btree indexes, because certain operations are
optimized in the case of unchanged columns; and even then, correctnesss
is not being compromised.

The values we pass after this commit are not fully trustworthy either,
because we simply say "all columns were updated" for all insert/updates,
regardless of whether their values were actually modified or not.
However, this way we err to the side of caution rather than to the
opposite direction as we were originally doing. This could be refined
in the future, but there's a trade-off: determining whether the column
was in fact updated could be expensive.

Author: Antonin Houska <ah(at)cybertec(dot)at>
Reviewed-by: Ewan Young <kdbase(dot)hack(at)gmail(dot)com>
Backpatch-through: 19
Discussion: https://postgr.es/m/18222.1782126731@localhost

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5ee9d7c299f2fe2f29db18c6448f798950efe22e

Modified Files
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src/backend/commands/repack.c | 57 +++++++++++++++++++++++++++++++++++++++++--
1 file changed, 55 insertions(+), 2 deletions(-)