Redis error: CROSSSLOT Keys in request don't hash to the same slot

[kiatng]

I am clueless on redis. We have a new OM instance running in AWS with ElasticCache, which was setup by a freelancer. Anyone has any idea on the following exception?

a:5:{i:0;s:98:"Error cleaning cache by mode matchingAnyTag: CROSSSLOT Keys in request don't hash to the same slot";i:1;s:1971:"#0 root/vendor/colinmollenhour/cache-backend-redis/Cm/Cache/Backend/Redis.php(1010): Zend_Cache::throwException()
#1 root/vendor/shardj/zf1-future/library/Zend/Cache/Core.php(466): Cm_Cache_Backend_Redis->clean()
#2 root/lib/Varien/Cache/Core.php(199): Zend_Cache_Core->clean()
#3 root/app/code/core/Mage/Core/Model/Cache.php(422): Varien_Cache_Core->clean()
#4 root/app/code/core/Mage/Core/Model/App.php(1234): Mage_Core_Model_Cache->clean()
#5 root/app/code/core/Mage/Core/Model/Abstract.php(496): Mage_Core_Model_App->cleanCache()
#6 root/app/code/core/Mage/Core/Model/Abstract.php(401): Mage_Core_Model_Abstract->cleanModelCache()
#7 root/app/code/core/Mage/Core/Model/Resource/Abstract.php(97): Mage_Core_Model_Abstract->afterCommitCallback()
#8 root/app/code/core/Mage/Core/Model/Abstract.php(383): Mage_Core_Model_Resource_Abstract->commit()
#9 root/app/code/local/Mage/Sales/Model/Quote.php(1970): Mage_Core_Model_Abstract->save()
#10 root/app/code/core/Mage/Checkout/Model/Cart.php(450): Mage_Sales_Model_Quote->save()
#11 root/app/code/core/Mage/Checkout/controllers/CartController.php(151): Mage_Checkout_Model_Cart->save()
#12 root/app/code/core/Mage/Core/Controller/Varien/Action.php(424): Mage_Checkout_CartController->indexAction()
#13 root/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(255): Mage_Core_Controller_Varien_Action->dispatch()
#14 root/app/code/core/Mage/Core/Controller/Varien/Front.php(181): Mage_Core_Controller_Varien_Router_Standard->match()
#15 root/app/code/core/Mage/Core/Model/App.php(358): Mage_Core_Controller_Varien_Front->dispatch()
#16 root/app/Mage.php(758): Mage_Core_Model_App->run()
#17 root/index.php(68): Mage::run()
#18 root/pub/storex_view/index.php(9): require('...')
#19 {main}";s:3:"url";s:15:"/checkout/cart/";s:11:"script_name";s:10:"/index.php";s:4:"skin";s:9:"storex_view";}

local.xml:

        <!-- @link https://github.com/colinmollenhour/Cm_RedisSession -->
        <session_save>db</session_save>
        <redis_session>
            <host>tls://xxx.serverless.apse1.cache.amazonaws.com</host>            <!-- Specify an absolute path if using a unix socket -->
            <port>6379</port>
            <password></password>             <!-- Specify if your Redis server requires authentication -->
            <timeout>2.5</timeout>            <!-- This is the Redis connection timeout, not the locking timeout -->
            <persistent></persistent>         <!-- Specify unique string to enable persistent connections. E.g.: sess-db0; bugs with phpredis and php-fpm are known: https://github.com/nicolasff/phpredis/issues/70 -->
            <db>0</db>                        <!-- Redis database number; protection from accidental loss is improved by using a unique DB number for sessions -->
            <compression_threshold>2048</compression_threshold>  <!-- Known bug with strings over 64k: https://github.com/colinmollenhour/Cm_Cache_Backend_Redis/issues/18 -->
            <compression_lib>gzip</compression_lib>              <!-- gzip, lzf, lz4, snappy or none to disable compression -->
            <log_level>1</log_level>               <!-- 0 (emergency: system is unusable), 4 (warning; additional information, recommended), 5 (notice: normal but significant condition), 6 (info: informational messages), 7 (debug: the most information for development/testing) -->
            <max_concurrency>6</max_concurrency>                 <!-- maximum number of processes that can wait for a lock on one session; for large production clusters, set this to at least 10% of the number of PHP processes -->
            <break_after_frontend>5</break_after_frontend>       <!-- seconds to wait for a session lock in the frontend; not as critical as admin -->
            <fail_after>10</fail_after>                          <!-- seconds after which we bail from attempting to obtain lock (in addition to break after time) -->
            <break_after_adminhtml>30</break_after_adminhtml>
            <first_lifetime>600</first_lifetime>                 <!-- Lifetime of session for non-bots on the first write. 0 to disable -->
            <bot_first_lifetime>60</bot_first_lifetime>          <!-- Lifetime of session for bots on the first write. 0 to disable -->
            <bot_lifetime>7200</bot_lifetime>                    <!-- Lifetime of session for bots on subsequent writes. 0 to disable -->
            <disable_locking>0</disable_locking>                 <!-- Disable session locking entirely. -->
            <min_lifetime>60</min_lifetime>                      <!-- Set the minimum session lifetime -->
            <max_lifetime>2592000</max_lifetime>                 <!-- Set the maximum session lifetime -->
            <log_exceptions>0</log_exceptions>                   <!-- Log connection failure and concurrent connection exceptions in exception.log. -->
        </redis_session>
        <!-- @see https://github.com/colinmollenhour/Cm_Cache_Backend_Redis -->
        <cache>
            <backend>Cm_Cache_Backend_Redis</backend>
            <backend_options>
                <server>tls://xxx.serverless.apse1.cache.amazonaws.com</server> <!-- or absolute path to unix socket -->
                <port>6379</port>
                <persistent></persistent> <!-- Specify unique string to enable persistent connections. E.g.: sess-db0; bugs with phpredis and php-fpm are known: https://github.com/nicolasff/phpredis/issues/70 -->
                <database>0</database> <!-- Redis database number; protection against accidental data loss is improved by not sharing databases -->
                <password></password> <!-- Specify if your Redis server requires authentication -->
                <force_standalone>0</force_standalone>  <!-- 0 for phpredis, 1 for standalone PHP -->
                <connect_retries>1</connect_retries>    <!-- Reduces errors due to random connection failures; a value of 1 will not retry after the first failure -->
                <read_timeout>10</read_timeout>         <!-- Set read timeout duration; phpredis does not currently support setting read timeouts -->
                <automatic_cleaning_factor>0</automatic_cleaning_factor> <!-- Disabled by default -->
                <compress_data>1</compress_data>  <!-- 0-9 for compression level, recommended: 0 or 1 -->
                <compress_tags>1</compress_tags>  <!-- 0-9 for compression level, recommended: 0 or 1 -->
                <compress_threshold>20480</compress_threshold>  <!-- Strings below this size will not be compressed -->
                <compression_lib>gzip</compression_lib> <!-- Supports gzip, lzf, lz4 (as l4z), snappy and zstd -->
                <use_lua>0</use_lua> <!-- Set to 1 if Lua scripts should be used for some operations (recommended) -->
            </backend_options>
        </cache>

[m-overlund]

cache and sessions shouldn't be in the same db

[kiatng]

I changed <db>0</db> to <db>1</db>. Now the error is

ERR SELECT is not allowed in cluster mode

#0 /var/web/edumsia/vendor/colinmollenhour/credis/Client.php(771): Credis_Client->__call()
#1 /var/web/edumsia/vendor/colinmollenhour/php-redis-session-abstract/src/Cm/RedisSession/Handler.php(455): Credis_Client->select()
#2 /var/web/edumsia/app/code/community/Cm/RedisSession/Model/Session.php(119): Cm\RedisSession\Handler->read()
#3 [internal function]: Cm_RedisSession_Model_Session->read()
#4 /var/web/edumsia/app/code/core/Mage/Core/Model/Session/Abstract/Varien.php(156): session_start()
#5 /var/web/edumsia/app/code/core/Mage/Core/Model/Session/Abstract/Varien.php(273): Mage_Core_Model_Session_Abstract_Varien->start()
#6 /var/web/edumsia/app/code/core/Mage/Core/Model/Session/Abstract.php(79): Mage_Core_Model_Session_Abstract_Varien->init()
#7 /var/web/edumsia/app/code/core/Mage/Core/Model/Session.php(43): Mage_Core_Model_Session_Abstract->init()
#8 /var/web/edumsia/app/code/core/Mage/Core/Model/Config.php(1478): Mage_Core_Model_Session->__construct()
#9 /var/web/edumsia/app/Mage.php(542): Mage_Core_Model_Config->getModelInstance()
#10 /var/web/edumsia/app/Mage.php(556): Mage::getModel()
#11 /var/web/edumsia/app/code/core/Mage/Core/Controller/Varien/Action.php(498): Mage::getSingleton()
#12 /var/web/edumsia/app/code/core/Mage/Core/Controller/Front/Action.php(57): Mage_Core_Controller_Varien_Action->preDispatch()
#13 /var/web/edumsia/app/code/core/Mage/Checkout/controllers/CartController.php(119): Mage_Core_Controller_Front_Action->preDispatch()
#14 /var/web/edumsia/app/code/core/Mage/Core/Controller/Varien/Action.php(413): Mage_Checkout_CartController->preDispatch()
#15 /var/web/edumsia/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(255): Mage_Core_Controller_Varien_Action->dispatch()
#16 /var/web/edumsia/app/code/core/Mage/Core/Controller/Varien/Front.php(181): Mage_Core_Controller_Varien_Router_Standard->match()
#17 /var/web/edumsia/app/code/core/Mage/Core/Model/App.php(358): Mage_Core_Controller_Varien_Front->dispatch()
#18 /var/web/edumsia/app/Mage.php(758): Mage_Core_Model_App->run()
#19 /var/web/edumsia/index.php(68): Mage::run()
#20 /var/web/edumsia/pub/visa_view/index.php(9): require('...')
#21 {main}

[kiatng]

Redis Cluster:

• In a Redis Cluster setup, you cannot configure multiple databases as you would in standalone Redis.
• Redis Cluster only supports a single logical database, which is database 0.
• The SELECT command (used to switch between databases) is not allowed in Redis Cluster.
• All keys and data reside within this single database.

Non-Clustered (Standalone) Redis:
In standalone Redis (non-clustered), you have more flexibility:

• By default, Redis supports 16 logical databases (numbered from 0 to 15).
• Each database is independent and isolated from the others.
• You can use the SELECT command to switch between databases (e.g., SELECT 1 for database 1).

[kiatng]

There are 3 possible options with ElasticCache in cluster mode:

1. Do not use redis for backend cache.
2. Disable cluster mode in ElasticCache.
3. Add a new instance of non-cluster ElasticCache for backend cache.