From e396f853a06ddd5adb9a20f80d4020d072ea3b2b Mon Sep 17 00:00:00 2001
From: AlexYue <yj976240184@gmail.com>
Date: Thu, 25 Jul 2024 12:17:38 +0800
Subject: [PATCH] Pick "[enhance](Cooldown) Use config to control whether use
 cooldown replica for scanning first" (#38322)

## Proposed changes

<!--Describe your changes.-->

Same as master #37492
---
 .../java/org/apache/doris/common/Config.java  |  3 ++
 .../apache/doris/planner/OlapScanNode.java    | 42 ++++++++++---------
 2 files changed, 25 insertions(+), 20 deletions(-)

diff --git a/fe/fe-common/src/main/java/org/apache/doris/common/Config.java b/fe/fe-common/src/main/java/org/apache/doris/common/Config.java
index 5a811fddd6..441a6a7c46 100644
--- a/fe/fe-common/src/main/java/org/apache/doris/common/Config.java
+++ b/fe/fe-common/src/main/java/org/apache/doris/common/Config.java
@@ -2735,6 +2735,9 @@ public class Config extends ConfigBase {
             "Stream_Load When importing, the maximum length of label is limited"})
     public static int label_regex_length = 128;
 
+    @ConfField(mutable = true)
+    public static boolean enable_cooldown_replica_affinity = true;
+
     //==========================================================================
     //                      end of cloud config
     //==========================================================================
diff --git a/fe/fe-core/src/main/java/org/apache/doris/planner/OlapScanNode.java b/fe/fe-core/src/main/java/org/apache/doris/planner/OlapScanNode.java
index d312992bc8..52104f6e66 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/planner/OlapScanNode.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/planner/OlapScanNode.java
@@ -836,27 +836,29 @@ public class OlapScanNode extends ScanNode {
                 }
             }
 
-            final long coolDownReplicaId = tablet.getCooldownReplicaId();
-            // we prefer to query using cooldown replica to make sure the cache is fully utilized
-            // for example: consider there are 3BEs(A,B,C) and each has one replica for tablet X. and X
-            // is now under cooldown
-            // first time we choose BE A, and A will download data into cache while the other two's cache is empty
-            // second time we choose BE B, this time B will be cached, C is still empty
-            // third time we choose BE C, after this time all replica is cached
-            // but it means we will do 3 S3 IO to get the data which will bring 3 slow query
-            if (-1L != coolDownReplicaId) {
-                final Optional<Replica> replicaOptional = replicas.stream()
-                        .filter(r -> r.getId() == coolDownReplicaId).findAny();
-                replicaOptional.ifPresent(
-                        r -> {
-                            Backend backend = Env.getCurrentSystemInfo()
-                                    .getBackend(r.getBackendId());
-                            if (backend != null && backend.isAlive()) {
-                                replicas.clear();
-                                replicas.add(r);
+            if (Config.enable_cooldown_replica_affinity) {
+                final long coolDownReplicaId = tablet.getCooldownReplicaId();
+                // we prefer to query using cooldown replica to make sure the cache is fully utilized
+                // for example: consider there are 3BEs(A,B,C) and each has one replica for tablet X. and X
+                // is now under cooldown
+                // first time we choose BE A, and A will download data into cache while the other two's cache is empty
+                // second time we choose BE B, this time B will be cached, C is still empty
+                // third time we choose BE C, after this time all replica is cached
+                // but it means we will do 3 S3 IO to get the data which will bring 3 slow query
+                if (-1L != coolDownReplicaId) {
+                    final Optional<Replica> replicaOptional = replicas.stream()
+                            .filter(r -> r.getId() == coolDownReplicaId).findAny();
+                    replicaOptional.ifPresent(
+                            r -> {
+                                Backend backend = Env.getCurrentSystemInfo()
+                                        .getBackend(r.getBackendId());
+                                if (backend != null && backend.isAlive()) {
+                                    replicas.clear();
+                                    replicas.add(r);
+                                }
                             }
-                        }
-                );
+                    );
+                }
             }
             boolean tabletIsNull = true;
             boolean collectedStat = false;