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From "Qifan Chen (Code Review)" <>
Subject [Impala-ASF-CR] IMPALA-9744: Treat corrupt table stats as missing to avoid bad plans
Date Sat, 11 Jul 2020 04:09:53 GMT
Qifan Chen has uploaded a new patch set (#17). ( )

Change subject: IMPALA-9744: Treat corrupt table stats as missing to avoid bad plans

IMPALA-9744: Treat corrupt table stats as missing to avoid bad plans

This work addresses the current limitation in computing the total row
count for a Hive table in a scan. The row count can be incorrectly
computed as 0, even though there exists data in the Hive table. This
is the stats corruption at table level. Similar stats corruption
exists for a partition. The row count of a table or a partition
sometime can also be -1 which indicates a missing stats situation.

In the fix, as long as no partition in a Hive table exhibits any
missing or corrupt stats, the total row count for the table is computed
from the row counts in all partitions. Otherwise, Impala looks at
the table level stats particularly the table row count.

In addition, if the table stats is missing or corrupted, Impala
estimates a row count for the table, if feasible. This row count is
the sum of the row count from the partitions with good stats, and
an estimation of the number of rows in the partitions with missing or
corrupt stats. Such estimation also applies when some partition
has missing or corrupt stats.

One way to observe the fix is through the explain of queries scanning
Hive tables with missing or corrupted stats. The cardinality for any
full scan should be a positive value (i.e. the estimated row count),
instead of 'unavailable'.  At the beginning of the explain output,
that table is still listed in the WARNING section for potentially
corrupt table statistics.

1. Ran unit tests with queries documented in the case against Hive
   tables with the following configrations:
   a. No stats corruption in any partitions
   b. Stats corruption in some partitions
   c. Stats corruption in all partitions
2. Added two new tests in
   a. test_corrupted_stats_in_partitioned_Hive_tables
   b. test_corrupted_stats_in_unpartitioned_Hive_tables
3. Fixed failures in corrupt-stats.test
4. Ran "core" test

Change-Id: I9f4c64616ff7c0b6d5a48f2b5331325feeff3576
M fe/src/main/java/org/apache/impala/planner/
M testdata/workloads/functional-query/queries/QueryTest/corrupt-stats.test
M tests/metadata/
3 files changed, 173 insertions(+), 32 deletions(-)

  git pull ssh:// refs/changes/98/16098/17
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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I9f4c64616ff7c0b6d5a48f2b5331325feeff3576
Gerrit-Change-Number: 16098
Gerrit-PatchSet: 17
Gerrit-Owner: Qifan Chen <>
Gerrit-Reviewer: Aman Sinha <>
Gerrit-Reviewer: Impala Public Jenkins <>
Gerrit-Reviewer: Qifan Chen <>
Gerrit-Reviewer: Sahil Takiar <>
Gerrit-Reviewer: Tim Armstrong <>

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