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Append-Only Tables

Append-Only Tables is a table feature that forbids deleting data files that could be a result of the following:

Append-Only Tables is enabled on a delta table using delta.appendOnly table property (indirectly, through AppendOnlyTableFeature that is a FeatureAutomaticallyEnabledByMetadata and uses this table property).

Demo

Create a delta table with delta.appendOnly table property enabled.

CREATE TABLE tbl(a int)
USING delta
TBLPROPERTIES (
  'delta.appendOnly' = 'true'
)

Describe the detail of the delta table using DESCRIBE DETAIL command.

sql("desc detail tbl")
  .select("name", "properties", "minReaderVersion", "minWriterVersion", "tableFeatures")
  .show(truncate = false)

+-------------------------+--------------------------+----------------+----------------+------------------------+
|name                     |properties                |minReaderVersion|minWriterVersion|tableFeatures           |
+-------------------------+--------------------------+----------------+----------------+------------------------+
|spark_catalog.default.tbl|{delta.appendOnly -> true}|1               |2               |[appendOnly, invariants]|
+-------------------------+--------------------------+----------------+----------------+------------------------+

Insert a record.

INSERT INTO tbl
VALUES (1)

Delete a record. It should fail.

DELETE FROM tbl
WHERE a = 1

And it did 👍

org.apache.spark.sql.delta.DeltaUnsupportedOperationException: This table is configured to only allow appends. If you would like to permit updates or deletes, use 'ALTER TABLE null SET TBLPROPERTIES (delta.appendOnly=false)'.
  at org.apache.spark.sql.delta.DeltaErrorsBase.modifyAppendOnlyTableException(DeltaErrors.scala:890)
  at org.apache.spark.sql.delta.DeltaErrorsBase.modifyAppendOnlyTableException$(DeltaErrors.scala:886)
  at org.apache.spark.sql.delta.DeltaErrors$.modifyAppendOnlyTableException(DeltaErrors.scala:2884)
  at org.apache.spark.sql.delta.DeltaLog$.assertRemovable(DeltaLog.scala:947)
  at org.apache.spark.sql.delta.commands.DeleteCommand.$anonfun$run$2(DeleteCommand.scala:115)
  at org.apache.spark.sql.delta.commands.DeleteCommand.$anonfun$run$2$adapted(DeleteCommand.scala:114)
  at org.apache.spark.sql.delta.DeltaLog.withNewTransaction(DeltaLog.scala:216)
  at org.apache.spark.sql.delta.commands.DeleteCommand.$anonfun$run$1(DeleteCommand.scala:114)
  ...