Details
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Improvement
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Status: Open
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Major
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Resolution: Unresolved
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None
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None
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None
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ghx-label-12
Description
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.
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 |
+--------------------------------------------------------------+