Qifan Chen created IMPALA-11647:
-----------------------------------
Summary: Row size for source tables in a cross join query is set
to 0 in query plan
Key: IMPALA-11647
URL: https://issues.apache.org/jira/browse/IMPALA-11647
Project: IMPALA
Issue Type: Improvement
Components: Frontend
Reporter: Qifan Chen
The row-size in the following explain output for both source tables is set to
0B. On paper, it is possible to apply the count star optimization for such
queries and therefore set the row-size correctly.
{code:java}
explain select count(*) from store_sales a, store_sales b limit 500
+--------------------------------------------------------------+
| Explain String |
+--------------------------------------------------------------+
| Max Per-Host Resource Reservation: Memory=256.00KB Threads=5 |
| Per-Host Resource Estimates: Memory=10MB |
| |
| PLAN-ROOT SINK |
| | |
| 06:AGGREGATE [FINALIZE] |
| | output: count:merge(*) |
| | limit: 500 |
| | row-size=8B cardinality=1 |
| | |
| 05:EXCHANGE [UNPARTITIONED] |
| | |
| 03:AGGREGATE |
| | output: count(*) |
| | row-size=8B cardinality=1 |
| | |
| 02:NESTED LOOP JOIN [CROSS JOIN, BROADCAST] |
| | row-size=0B cardinality=8.30T |
| | |
| |--04:EXCHANGE [BROADCAST] |
| | | |
| | 01:SCAN HDFS [tpcds_parquet.store_sales b] |
| | HDFS partitions=1824/1824 files=1824 size=199.83MB |
| | row-size=0B cardinality=2.88M |
| | |
| 00:SCAN HDFS [tpcds_parquet.store_sales a] |
| HDFS partitions=1824/1824 files=1824 size=199.83MB |
| row-size=0B cardinality=2.88M |
+--------------------------------------------------------------+
{code}
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