From 2a400a0ad0201ea10c735adc0fe12487ac5552c3 Mon Sep 17 00:00:00 2001
From: Andy Grove <agrove@apache.org>
Date: Wed, 30 Sep 2026 06:24:23 -0600
Subject: [PATCH] fix: describe CometInMemoryTableScan by the scan it replaces
 in EXPLAIN

CometInMemoryTableScanExec printed every constructor field in its plan
string, among them the CachedRDDBuilder with the whole cached plan, physical
and logical, inline and with its raw newlines. That broke the tree of every
plan that read the cache, in EXPLAIN and EXPLAIN FORMATTED alike.

Print the Spark InMemoryTableScanExec it replaces instead, which shows the
table's name when it has one, the attributes read and any pruning predicates.
---
 .../comet/CometInMemoryTableScanExec.scala    |  6 +++
 .../comet/exec/CometInMemoryCacheSuite.scala  | 37 +++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/spark/src/main/scala/org/apache/spark/sql/comet/CometInMemoryTableScanExec.scala b/spark/src/main/scala/org/apache/spark/sql/comet/CometInMemoryTableScanExec.scala
index 103f95f2e53..7af36cac667 100644
--- a/spark/src/main/scala/org/apache/spark/sql/comet/CometInMemoryTableScanExec.scala
+++ b/spark/src/main/scala/org/apache/spark/sql/comet/CometInMemoryTableScanExec.scala
@@ -73,6 +73,12 @@ case class CometInMemoryTableScanExec(
   // for instance -- then reads the wrong column.
   override def output: Seq[Attribute] = originalPlan.output
 
+  // Described by the Spark scan it replaces: the table's name when it has one, the attributes it
+  // reads and any pruning predicates. The default would print every constructor field, among them
+  // the CachedRDDBuilder with the whole cached plan, physical and logical, inline and with its raw
+  // newlines, which breaks the tree of every plan that reads the cache.
+  override def stringArgs: Iterator[Any] = Iterator(originalPlan)
+
   // `originalPlan` is a plan-typed field rather than a child, so QueryPlan's canonicalization
   // walks straight past it: its attributes and predicates keep the expression IDs of whichever
   // occurrence of the cached relation produced them. Two scans of one cache then compare unequal,
diff --git a/spark/src/test/scala/org/apache/comet/exec/CometInMemoryCacheSuite.scala b/spark/src/test/scala/org/apache/comet/exec/CometInMemoryCacheSuite.scala
index ed3d518d3ce..d82f6c021bc 100644
--- a/spark/src/test/scala/org/apache/comet/exec/CometInMemoryCacheSuite.scala
+++ b/spark/src/test/scala/org/apache/comet/exec/CometInMemoryCacheSuite.scala
@@ -324,6 +324,43 @@ class CometInMemoryCacheSuite extends CometTestBase {
     }
   }
 
+  test("CometInMemoryTableScan is described by the Spark scan it replaces") {
+    // With every constructor field printed, the node dumped its CachedRDDBuilder, the whole cached
+    // plan both physical and logical, into the middle of every plan that read the cache, raw
+    // newlines and all, in the tree string and in EXPLAIN FORMATTED alike.
+    withSQLConf(
+      SQLConf.ADAPTIVE_EXECUTION_ENABLED.key -> "false",
+      CometConf.COMET_EXEC_IN_MEMORY_CACHE_ENABLED.key -> "true") {
+      spark.catalog.clearCache()
+      spark
+        .range(1000)
+        .selectExpr("id AS key", "id % 8 AS value")
+        .createOrReplaceTempView("explain_cache")
+      spark.catalog.cacheTable("explain_cache")
+      try {
+        val df = spark.sql("SELECT key FROM explain_cache WHERE value = 3")
+        df.collect()
+        val plan = df.queryExecution.executedPlan
+        val scans = collect(plan) { case s: CometInMemoryTableScanExec => s }
+        assert(scans.size == 1)
+        val line = scans.head.simpleString(SQLConf.get.maxToStringFields)
+        assert(
+          line.startsWith("CometInMemoryTableScan Scan In-memory table explain_cache ["),
+          line)
+        assert(line.contains("= 3)"), s"the pruning predicates should be shown: $line")
+        Seq(
+          plan.treeString,
+          df.queryExecution.explainString(org.apache.spark.sql.execution.FormattedMode))
+          .foreach { text =>
+            assert(!text.contains("CachedRDDBuilder"), text)
+            assert(!text.contains(classOf[ArrowCachedBatchSerializer].getName), text)
+          }
+      } finally {
+        spark.catalog.clearCache()
+      }
+    }
+  }
+
   test("Comet in-memory cache disabled keeps SparkToColumnar fallback path") {
     withSQLConf(
       SQLConf.ADAPTIVE_EXECUTION_ENABLED.key -> "false",