rowexec: problem with an empty tuple during spilling to disk

[yuzefovich]

The following logic test will fail when run via the row-by-row engine:

# LogicTest: local-vec-off

statement ok
SET distsql_workmem = '2B'

query T
SELECT
  col
FROM
  (VALUES ((ARRAY[]::RECORD[])), ((ARRAY[()])))
    AS t(col)
ORDER BY
  col ASC
----
{}
{()}

The idea is that we're forcing the sort to spill to disk, so both array go through encoding/decoding process. We have arrays of tuple, and we need to use the key encoding. The key encoding for both tuples ends up being the same.

Jira issue: CRDB-14222

[yuzefovich]

@rafiss given your work in #70767, does this issue seem important enough that we'll ever want to fix it? I think probably not, so I'm putting it straight on backlog.

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