From 9bcdf5d7460e4475d1a5cbe7e547c574e00e603b Mon Sep 17 00:00:00 2001
From: Dmitry Konstantinov <netudima@gmail.com>
Date: Mon, 6 Apr 2026 21:16:25 +0100
Subject: [PATCH] Avoid Cell iterator for alive rows in MetricsRecording
 transformation of ReadCommand

patch by Dmitry Konstantinov; reviewed by Francisco Guerrero for CASSANDRA-21288
---
 CHANGES.txt                                   |  1 +
 .../org/apache/cassandra/db/ReadCommand.java  | 19 ++++++++++++-------
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/CHANGES.txt b/CHANGES.txt
index b1451a0cdd..9be07b3a2b 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,4 +1,5 @@
 6.0-alpha2
+ * Avoid Cell iterator for alive rows in MetricsRecording transformation of ReadCommand (CASSANDRA-21288)
  * Reuse a single TrackedDataInputPlus instance per UnfilteredSerializer (CASSANDRA-21296)
  * In-tree docs are included in binary artifacts (tarball, deb, rpm) as html and man pages (CASSANDRA-17260)
  * Add tooling to repair system peers and peers_v2 if inconsistent with cluster metadata (CASSANDRA-21187)
diff --git a/src/java/org/apache/cassandra/db/ReadCommand.java b/src/java/org/apache/cassandra/db/ReadCommand.java
index f5f9105602..bc918e9f3e 100644
--- a/src/java/org/apache/cassandra/db/ReadCommand.java
+++ b/src/java/org/apache/cassandra/db/ReadCommand.java
@@ -644,19 +644,24 @@ public abstract class ReadCommand extends AbstractReadQuery
             public Row applyToRow(Row row)
             {
                 boolean hasTombstones = false;
-                for (Cell<?> cell : row.cells())
+                final long nowInSec = ReadCommand.this.nowInSec();
+                final boolean rowHasDeletion = row.hasDeletion(nowInSec);
+                if (rowHasDeletion) // perf optimization, to avoid iteration if all cells are alive
                 {
-                    if (!cell.isLive(ReadCommand.this.nowInSec()))
+                    for (Cell<?> cell : row.cells())
                     {
-                        countTombstone(row.clustering());
-                        hasTombstones = true; // allows to avoid counting an extra tombstone if the whole row expired
+                        if (!cell.isLive(nowInSec))
+                        {
+                            countTombstone(row.clustering());
+                            hasTombstones = true; // allows to avoid counting an extra tombstone if the whole row expired
+                        }
                     }
                 }
 
-                if (row.hasLiveData(ReadCommand.this.nowInSec(), enforceStrictLiveness))
+                if (row.hasLiveData(nowInSec, enforceStrictLiveness))
                     ++liveRows;
-                else if (!row.primaryKeyLivenessInfo().isLive(ReadCommand.this.nowInSec())
-                        && row.hasDeletion(ReadCommand.this.nowInSec())
+                else if (!row.primaryKeyLivenessInfo().isLive(nowInSec)
+                        && rowHasDeletion
                         && !hasTombstones)
                 {
                     // We're counting primary key deletions only here.