Gather partial TopN results #21761
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Gather partial TopN results #21761
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Dith3r
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martint
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| import static io.trino.sql.planner.plan.TopNNode.Step.PARTIAL; | ||
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| /** | ||
| * Adds local round-robin and gathering exchange on top of partial TopN to limit the task output size. |
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How big of an issue is this? For a leaf task, the output is currently N * number_of_splits. With this change, it's N. But if N is small, this may not be such big of a deal in general.
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here are some numbers
trino:iceberg_small_files_tpch_sf1000_orc_part> explain analyze verbose select * from lineitem order by orderkey limit 10000;
Before
Output: 2947463228 rows (419.40GB)
...
CPU Time: 18061.8s total, 332K rows/s, 9.04MB/s, 45% active
Per Node: 9.9 parallelism, 3.29M rows/s, 89.6MB/s
Parallelism: 69.4
Peak Memory: 1.07GB
4:20 [6B rows, 159GB] [23.1M rows/s, 627MB/s]
After
Output: 60000 rows (8.75MB)
...
CPU Time: 17139.7s total, 350K rows/s, 9.53MB/s, 34% active
Per Node: 17.7 parallelism, 6.2M rows/s, 169MB/s
Parallelism: 123.9
Peak Memory: 1.62GB
2:18 [6B rows, 159GB] [43.4M rows/s, 1.15GB/s]
core/trino-main/src/main/java/io/trino/SystemSessionProperties.java
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raunaqmorarka
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May 2, 2024
Gathering TopN avoids unnecessary network overhead, especially when both the number of splits and the TopN limit are big. Co-authored-by: Kamil Endruszkiewicz <kamil.endruszkiewicz@starburstdata.com>
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Description
Gathering TopN avoids unnecessary network overhead, especially when both the number of splits and the TopN limit are big.
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