commit b03cfcf2ade6dea7fed10f4a3db5c58ddf2c6bd2
author Zoltan Borok-Nagy <boroknagyz@cloudera.com> Fri Mar 22 19:16:07 2024 +0100
committer Impala Public Jenkins <impala-public-jenkins@cloudera.com> Thu Mar 28 15:17:40 2024 +0000
tree ffedc647e0074fcb6fa9301e57f94c1f58bf2bb1
parent 73171cb7164573349bd53a996a51bb7058b778e0

IMPALA-12894: (part 2) Fix optimized count(*) for Iceberg tables with dangling delete files

Impala can return incorrect results if a table has dangling delete
files. Dangling delete files are delete files that are part of the
snapshot but they are not applicable to any of the data files. We can
have such delete files after Spark's rewrite_data_files action.

During analysis we check the existence of delete files based on the
snapshot summary. If there are no delete files in the table, we just
replace the count(*) expression with NumericLiteral($record_count).
If there are delete files in the table (based on the summary), we set
optimize_count_star_for_iceberg_v2 in the query context.

Without optimize_count_star_for_iceberg_v2 in the query context, the
IcebergScanPlanner would create the following plan.

    AGGREGATE
    COUNT(*)
        |
    UNION ALL
   /         \
  /           \
 /             \
SCAN all    ANTI JOIN
datafiles  /         \
without   /           \
deletes  SCAN         SCAN
         datafiles    deletes
         with deletes

With optimize_count_star_for_iceberg_v2 the final plan looks like
the following:

      ArithmeticExpr(ADD)
      /             \
     /               \
    /                 \
record_count       AGGREGATE
of all             COUNT(*)
datafiles              |
without            ANTI JOIN
deletes           /         \
                 /           \
                SCAN        SCAN
                datafiles   deletes
                with deletes

The ArithmeticExpr(ADD) and its left child (record_count) is created
by the analyzer, IcebergScanPlanner is responsible in creating the
plan under AGGREGATE COUNT(*). And if it has delete files and
optimize_count_star_for_iceberg_v2 is true, it knows it can omit
the original UNION ALL and its left child.

However, IcebergScanPlanner checks delete file existence based on the
result of planFiles(), hence dangling delete files are eliminated.
And if there are no delete files, IcebergScanPlanner assumes that
case is already handled by the Analyzer (i.e. it replaced count(*)
with NumericLiteral($record_count)). So it will incorrectly create a
normal SCAN plan of the table under COUNT(*), i.e. we end up
with this:

      ArithmeticExpr(ADD)
      /             \
     /               \
    /                 \
record_count       AGGREGATE
of all             COUNT(*)
datafiles              |
without              SCAN
deletes            datafiles
                   without
                   deletes

Which means Impala will yield $record_count * 2 as a result.

This patch fixes the FeIcebergTable.hasDeleteFiles() method, so it
also ignores dangling delete files. Therefore, the analyzer will just
substitute count(*) with NumericLiteral($record_count) if all deletes
are dangling, i.e. no need to involve the IcebergScanPlanner at all.

The patch also introduces a new query option,
"iceberg_disable_count_star_optimization", so users can completely
disable the statistic-based count(*)-optimization if necessary.

Testing:
 * e2e tests
 * planner tests

Change-Id: Ie3aca0b0a104f9ca4589cde9643f3f341d4ff99f
Reviewed-on: http://gerrit.cloudera.org:8080/21190
Reviewed-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>