Add number option to preserve in Iceberg expire_snapshots

plugin/trino-iceberg/src/main/java/io/trino/plugin/iceberg/IcebergMetadata.java

@@ -142,6 +142,7 @@
 import org.apache.iceberg.DataFiles;
 import org.apache.iceberg.DeleteFile;
 import org.apache.iceberg.DeleteFiles;
+import org.apache.iceberg.ExpireSnapshots;
 import org.apache.iceberg.FileFormat;
 import org.apache.iceberg.FileMetadata;
 import org.apache.iceberg.FileScanTask;
@@ -1707,12 +1708,13 @@ private Optional<ConnectorTableExecuteHandle> getTableHandleForDropExtendedStats
     private Optional<ConnectorTableExecuteHandle> getTableHandleForExpireSnapshots(ConnectorSession session, IcebergTableHandle tableHandle, Map<String, Object> executeProperties)
     {
         Duration retentionThreshold = (Duration) executeProperties.get(RETENTION_THRESHOLD);
+        Optional<Integer> retainLast = Optional.ofNullable((Integer) executeProperties.get("retain_last"));
         Table icebergTable = catalog.loadTable(session, tableHandle.getSchemaTableName());
 
         return Optional.of(new IcebergTableExecuteHandle(
                 tableHandle.getSchemaTableName(),
                 EXPIRE_SNAPSHOTS,
-                new IcebergExpireSnapshotsHandle(retentionThreshold),
+                new IcebergExpireSnapshotsHandle(retentionThreshold, retainLast),
                 icebergTable.location(),
                 icebergTable.io().properties()));
     }
@@ -2174,11 +2176,12 @@ private void executeExpireSnapshots(ConnectorSession session, IcebergTableExecut
             }
         };
 
+        ExpireSnapshots expireSnapshots = table.expireSnapshots()
+                .expireOlderThan(expireTimestampMillis)
+                .deleteWith(deleteFunction);
+        expireSnapshotsHandle.retainLast().ifPresent(expireSnapshots::retainLast);
         try {
-            table.expireSnapshots()
-                    .expireOlderThan(expireTimestampMillis)
-                    .deleteWith(deleteFunction)
-                    .commit();
+            expireSnapshots.commit();
 
             fileSystem.deleteFiles(pathsToDelete);
         }

plugin/trino-iceberg/src/main/java/io/trino/plugin/iceberg/procedure/ExpireSnapshotsTableProcedure.java

@@ -16,11 +16,14 @@
 import com.google.common.collect.ImmutableList;
 import com.google.inject.Provider;
 import io.airlift.units.Duration;
+import io.trino.spi.TrinoException;
 import io.trino.spi.connector.TableProcedureMetadata;
 
 import static io.trino.plugin.base.session.PropertyMetadataUtil.durationProperty;
 import static io.trino.plugin.iceberg.procedure.IcebergTableProcedureId.EXPIRE_SNAPSHOTS;
+import static io.trino.spi.StandardErrorCode.INVALID_PROCEDURE_ARGUMENT;
 import static io.trino.spi.connector.TableProcedureExecutionMode.coordinatorOnly;
+import static io.trino.spi.session.PropertyMetadata.integerProperty;
 
 public class ExpireSnapshotsTableProcedure
         implements Provider<TableProcedureMetadata>
@@ -36,6 +39,16 @@ public TableProcedureMetadata get()
                                 "retention_threshold",
                                 "Only snapshots older than threshold should be removed",
                                 Duration.valueOf("7d"),
+                                false),
+                        integerProperty(
+                                "retain_last",
+                                "Number of ancestor snapshots to preserve regardless of retention_threshold (defaults to 1)",
+                                null,
+                                value -> {
+                                    if (value < 1) {
+                                        throw new TrinoException(INVALID_PROCEDURE_ARGUMENT, "retain_last must be at least 1, cannot be: %s".formatted(value));
+                                    }
+                                },
                                 false)));
     }
 }

plugin/trino-iceberg/src/main/java/io/trino/plugin/iceberg/procedure/IcebergExpireSnapshotsHandle.java

@@ -13,15 +13,29 @@
  */
 package io.trino.plugin.iceberg.procedure;
 
+import com.google.common.base.MoreObjects;
 import io.airlift.units.Duration;
 
+import java.util.Optional;
+
 import static java.util.Objects.requireNonNull;
 
-public record IcebergExpireSnapshotsHandle(Duration retentionThreshold)
+public record IcebergExpireSnapshotsHandle(Duration retentionThreshold, Optional<Integer> retainLast)
         implements IcebergProcedureHandle
 {
     public IcebergExpireSnapshotsHandle
     {
         requireNonNull(retentionThreshold, "retentionThreshold is null");
+        requireNonNull(retainLast, "retainLast is null");
+    }
+
+    @Override
+    public String toString()
+    {
+        return MoreObjects.toStringHelper(this)
+                .omitEmptyValues()
+                .add("retentionThreshold", retentionThreshold)
+                .add("retainLast", retainLast)
+                .toString();
     }
 }

plugin/trino-iceberg/src/test/java/io/trino/plugin/iceberg/BaseIcebergConnectorTest.java

@@ -6473,6 +6473,32 @@ public void testExpireSnapshotsPartitionedTable()
         assertThat(updatedSnapshots.size()).isLessThan(initialSnapshots.size());
     }
 
+    @Test
+    public void testExpireSnapshotsRetainLast()
+            throws Exception
+    {
+        String tableName = "test_expiring_snapshots_" + randomNameSuffix();
+        Session sessionWithShortRetentionUnlocked = prepareCleanUpSession();
+        assertUpdate("CREATE TABLE " + tableName + " (key varchar, value integer)");
+        assertUpdate("INSERT INTO " + tableName + " VALUES ('one', 1)", 1);
+        assertUpdate("INSERT INTO " + tableName + " VALUES ('two', 2)", 1);
+        assertUpdate("INSERT INTO " + tableName + " VALUES ('three', 3)", 1);
+        assertThat(query("SELECT count(*) FROM " + tableName)).matches("VALUES BIGINT '3'");
+
+        List<Long> initialSnapshots = getSnapshotIds(tableName);
+        String tableLocation = getTableLocation(tableName);
+        List<String> initialFiles = getAllMetadataFilesFromTableDirectory(tableLocation);
+        assertQuerySucceeds(sessionWithShortRetentionUnlocked, "ALTER TABLE " + tableName + " EXECUTE expire_snapshots(retention_threshold => '0s', retain_last => 2)");
+
+        assertThat(query("SELECT count(*) FROM " + tableName)).matches("VALUES BIGINT '3'");
+        List<String> updatedFiles = getAllMetadataFilesFromTableDirectory(tableLocation);
+        List<Long> updatedSnapshots = getSnapshotIds(tableName);
+        assertThat(updatedFiles).hasSize(initialFiles.size() - 2);
+        assertThat(updatedSnapshots.size()).isLessThan(initialSnapshots.size());
+        assertThat(updatedSnapshots).hasSize(2);
+        assertThat(initialSnapshots).containsAll(updatedSnapshots);
+    }
+
     @Test
     public void testExpireSnapshotsOnSnapshot()
     {
@@ -6525,6 +6551,9 @@ public void testExpireSnapshotsParameterValidation()
         assertQueryFails(
                 "ALTER TABLE nation EXECUTE EXPIRE_SNAPSHOTS (retention_threshold => '33s')",
                 "\\QRetention specified (33.00s) is shorter than the minimum retention configured in the system (7.00d). Minimum retention can be changed with iceberg.expire-snapshots.min-retention configuration property or iceberg.expire_snapshots_min_retention session property");
+        assertQueryFails(
+                "ALTER TABLE nation EXECUTE EXPIRE_SNAPSHOTS (retention_threshold => '10d', retain_last => 0)",
+                ".* retain_last must be at least 1, cannot be: 0");
     }
 
     @Test