[SPARK-28595][SQL] explain should not trigger partition listing #25328
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I agree that it was very hard to meet the condition. BTW, IIRC, the main reason for that optimization was to get the same result with
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Test build #108525 has finished for PR 25328 at commit
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I don't think a system needs to guarantee the output order of a SQL query without ORDER BY. But let me add a legacy config to keep this optimization, just in case. what do you think @dongjoon-hyun ? |
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Test build #108571 has finished for PR 25328 at commit
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Test build #108688 has finished for PR 25328 at commit
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sql/core/src/main/scala/org/apache/spark/sql/execution/DataSourceScanExec.scala
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retest this please |
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Test build #108699 has finished for PR 25328 at commit
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Test build #108700 has finished for PR 25328 at commit
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| protected override def afterAll(): Unit = { | ||
| spark.sessionState.conf.unsetConf(SQLConf.LEGACY_BUCKETED_TABLE_SCAN_OUTPUT_ORDERING) |
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Should we do a "store and recover the old conf" instead?
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In the test, we assume that every test suite will keep the shared SparkSession clean after tests are run. So the old conf should be the default conf here, and we only need to call unsetConf to restore the default config.
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LGTM except one minor comment https://github.com/apache/spark/pull/25328/files#r311096949. |
| sql("CREATE TABLE t USING json PARTITIONED BY (j) AS SELECT 1 i, 2 j") | ||
| assert(HiveCatalogMetrics.METRIC_PARTITIONS_FETCHED.getCount == 0) | ||
| spark.table("t").explain() | ||
| assert(HiveCatalogMetrics.METRIC_PARTITIONS_FETCHED.getCount == 0) |
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Add a test case that can return non-zero when spark.sql.legacy.bucketedTableScan.outputOrdering is set to true?
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LGTM except one comment. |
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Test build #108745 has finished for PR 25328 at commit
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Test build #108747 has finished for PR 25328 at commit
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retest this please |
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Test build #108753 has finished for PR 25328 at commit
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thanks for the review, merging to master! |
What changes were proposed in this pull request?
Sometimes when you explain a query, you will get stuck for a while. What's worse, you will get stuck again if you explain again.
This is caused by
FileSourceScanExec:toString, it needs to report the number of partitions it reads. This needs to query the hive metastore.outputOrdering, it needs to get all the files. This needs to query the hive metastore.This PR fixes by:
toStringdo not need to report the number of partitions it reads. We should report it via SQL metrics.outputOrderingis not very useful. We can only apply it if a) all the bucket columns are read. b) there is only one file in each bucket. This condition is really hard to meet, and even if we meet, sorting an already sorted file is pretty fast and avoiding the sort is not that useful. I think it's worth to give up this optimization so that explain don't need to get stuck.How was this patch tested?
existing tests