From 841d59ef81b2eb9018e43fd9e8ae5b1adce3dc31 Mon Sep 17 00:00:00 2001
From: Colin Mollenhour <colin@mollenhour.com>
Date: Thu, 29 Dec 2022 14:46:03 -0500
Subject: [PATCH] Handle LOADING exception during read. (#171)

Handle LOADING state when reading from slave by reading from master and when reading from master by retrying after 1 second wait.
---
 Cm/Cache/Backend/Redis.php | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/Cm/Cache/Backend/Redis.php b/Cm/Cache/Backend/Redis.php
index 5e39b70..b620775 100644
--- a/Cm/Cache/Backend/Redis.php
+++ b/Cm/Cache/Backend/Redis.php
@@ -480,16 +480,35 @@ protected function _setupReadWriteCluster($options)
     public function load($id, $doNotTestCacheValidity = false)
     {
         if ($this->_slave) {
-            $data = $this->_slave->hGet(self::PREFIX_KEY.$id, self::FIELD_DATA);
+            try {
+                $data = $this->_slave->hGet(self::PREFIX_KEY.$id, self::FIELD_DATA);
 
-            // Prevent compounded effect of cache flood on asynchronously replicating master/slave setup
-            if ($this->_retryReadsOnMaster && $data === false) {
-                $data = $this->_redis->hGet(self::PREFIX_KEY.$id, self::FIELD_DATA);
+                // Prevent compounded effect of cache flood on asynchronously replicating master/slave setup
+                if ($this->_retryReadsOnMaster && $data === false) {
+                    $data = $this->_redis->hGet(self::PREFIX_KEY.$id, self::FIELD_DATA);
+                }
+            } catch (CredisException $e) {
+                // Always retry reads on master when dataset is loading on slave
+                if ($e->getMessage() === 'LOADING Redis is loading the dataset in memory') {
+                    $data = $this->_redis->hGet(self::PREFIX_KEY.$id, self::FIELD_DATA);
+                } else {
+                    throw $e;
+                }
             }
         } else {
-            $data = $this->_redis->hGet(self::PREFIX_KEY.$id, self::FIELD_DATA);
+            try {
+                $data = $this->_redis->hGet(self::PREFIX_KEY.$id, self::FIELD_DATA);
+            } catch (CredisException $e) {
+                // Retry once after 1 second when dataset is loading
+                if ($e->getMessage() === 'LOADING Redis is loading the dataset in memory') {
+                    sleep(1);
+                    $data = $this->_redis->hGet(self::PREFIX_KEY.$id, self::FIELD_DATA);
+                } else {
+                    throw $e;
+                }
+            }
         }
-        if ($data === NULL || is_object($data)) {
+        if ($data === NULL || $data === FALSE || is_object($data)) {
             return FALSE;
         }