[spark] Make saveAsTable+overwrite behave as INSERT OVERWRITE#8225
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Previously, df.write.mode("overwrite").saveAsTable("t") produced a
ReplaceTableAsSelect plan which could drop+recreate the table if the
user did not re-specify partitionBy() and primary-key options.
Now on Spark 3.4+, saveAsTable+overwrite is rewritten to
OverwriteByExpression (or OverwritePartitionsDynamic when
partitionOverwriteMode=dynamic), preserving the existing table
definition (partitions, primary keys, properties). This aligns with
the behavior of INSERT OVERWRITE and is consistent with Delta Lake.
SQL CREATE OR REPLACE TABLE AS SELECT and V2 writeTo().replace()
are not affected.
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Purpose
Previously,
df.write.mode("overwrite").saveAsTable("t")produced aReplaceTableAsSelectplan, which could drop + recreate the table when the user did not re-specifypartitionBy()and primary-key options — silently losing the partition spec, primary keys, and table properties.This PR makes
saveAsTable+overwriteon an existing table (Spark 3.4+) be rewritten toOverwriteByExpression(orOverwritePartitionsDynamicwhenpartitionOverwriteMode=dynamic), preserving the existing table definition. This aligns with the behavior ofINSERT OVERWRITEand is consistent with Delta Lake.SQL
CREATE OR REPLACE TABLE AS SELECTand V2writeTo().replace()are not affected.Tests
Added cases in
DataFrameWriteTestBase:saveAsTable overwrite preserves table definition and snapshotssaveAsTable overwrite on non-partitioned tablesaveAsTable overwrite creates table when not existssaveAsTable overwrite respects dynamic partition overwrite mode