feat(small): Support <slt:ignore> marker in sqllogictest for non-deterministic expected parts

datafusion/sqllogictest/README.md

@@ -142,6 +142,17 @@ select substr('Andrew Lamb', 1, 6), '|'
 Andrew |
 ```
 
+## Cookbook: Ignoring volatile output
+
+Sometimes parts of a result change every run (timestamps, counters, etc). To keep the rest of the snapshot checked in, replace those fragments with the `<slt:ignore>` marker inside the expected block. During validation the marker acts like a wildcard, so only the surrounding text must match.
+
+```text
+query TT
+EXPLAIN ANALYZE SELECT * FROM generate_series(100);
+----
+Plan with Metrics LazyMemoryExec: partitions=1, batch_generators=[generate_series: start=0, end=100, batch_size=8192], metrics=[output_rows=101, elapsed_compute=<slt:ignore>, output_bytes=<slt:ignore>]
+```
+
 # Reference
 
 ## Running tests: Validation Mode

datafusion/sqllogictest/src/util.rs

@@ -82,13 +82,36 @@ pub fn df_value_validator(
     actual: &[Vec<String>],
     expected: &[String],
 ) -> bool {
+    // Support ignore marker <slt:ignore> to skip volatile parts of output.
+    const IGNORE_MARKER: &str = "<slt:ignore>";
+    let contains_ignore_marker = expected.iter().any(|line| line.contains(IGNORE_MARKER));
+
     let normalized_expected = expected.iter().map(normalizer).collect::<Vec<_>>();
     let normalized_actual = actual
         .iter()
         .map(|strs| strs.iter().join(" "))
         .map(|str| str.trim_end().to_string())
         .collect_vec();
 
+    // If ignore marker present, perform fragment-based matching on the full snapshot.
+    if contains_ignore_marker {
+        let expected_snapshot = normalized_expected.join("\n");
+        let actual_snapshot = normalized_actual.join("\n");
+        let fragments: Vec<&str> = expected_snapshot.split(IGNORE_MARKER).collect();
+        let mut pos = 0;
+        for frag in fragments {
+            if frag.is_empty() {
+                continue;
+            }
+            if let Some(idx) = actual_snapshot[pos..].find(frag) {
+                pos += idx + frag.len();
+            } else {
+                return false;
+            }
+        }
+        return true;
+    }
+
     if log_enabled!(Warn) && normalized_actual != normalized_expected {
         warn!("df validation failed. actual vs expected:");
         for i in 0..normalized_actual.len() {

datafusion/sqllogictest/test_files/explain_analyze.slt

@@ -0,0 +1,27 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+statement ok
+set datafusion.explain.analyze_level = summary;
+
+query TT
+EXPLAIN ANALYZE SELECT * FROM generate_series(100);
+----
+Plan with Metrics LazyMemoryExec: partitions=1, batch_generators=[generate_series: start=0, end=100, batch_size=8192], metrics=[output_rows=101, elapsed_compute=<slt:ignore>, output_bytes=<slt:ignore>]
+
+statement ok
+reset datafusion.explain.analyze_level;