AWS Autodiscovery not working

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March 10, 2021 at 12:32 pm #34832
Mike
Guest
I have premium W3TC license and have elastic cache autodiscovery client installed.

In object/database cache settings I have entered the configuration endpoint and ticked box for auto discovery. If I click the test button it gives me a green pass tick.

Now if I view the source code of a page I get the following:
```

Notice: Undefined variable: s in /wpfiles/htdocs/wp-content/plugins/w3-total-cache/DbCache_WpdbInjection_QueryCaching.php on line 748

Notice: Undefined variable: d in /wpfiles/htdocs/wp-content/plugins/w3-total-cache/DbCache_WpdbInjection_QueryCaching.php on line 748

Notice: Undefined variable: s in /wpfiles/htdocs/wp-content/plugins/w3-total-cache/DbCache_WpdbInjection_QueryCaching.php on line 749

Notice: Undefined variable: d in /wpfiles/htdocs/wp-content/plugins/w3-total-cache/DbCache_WpdbInjection_QueryCaching.php on line 749

Notice: Undefined variable: s in /wpfiles/htdocs/wp-content/plugins/w3-total-cache/DbCache_WpdbInjection_QueryCaching.php on line 750
```
If I specify the node endpoint directly then it works but I need the autodiscovery to work as we have a cache cluster and adjust the number of nodes.

Why is it not working?
March 10, 2021 at 6:29 pm #34863
Marko Vasiljevic
Keymaster
Hello Mike,

Thank you for your inquiry and I am happy to assist you with this.

There is a possible issue in /wp-content/plugins/w3-total-cache/DbCache_WpdbInjection_QueryCaching.php lines 742-744.
Change the double-quotes to single:
```
$strings[] = sprintf( "%s%d", str_pad( 'Total queries: ', 20 ), $this->query_total );
$strings[] = sprintf( "%s%d", str_pad( 'Cached queries: ', 20 ), $this->query_hits );
$strings[] = sprintf( "%s%.4f", str_pad( 'Total query time: ', 20 ), $this->time_total
);
```
to
```
$strings[] = sprintf( '%s%d', str_pad( 'Total queries: ', 20 ), $this->query_total );
$strings[] = sprintf( '%s%d', str_pad( 'Cached queries: ', 20 ), $this->query_hits );
$strings[] = sprintf( '%s%.4f', str_pad( 'Total query time: ', 20 ), $this->time_total );
```
Try this out and let me know if this helps!

Thanks!
March 11, 2021 at 10:53 am #34869

Mike
Guest

Hi Marko,

Thanks for the reply. Adding the ‘ removed the notice but the issue still remains,

With normal php memcached client I am able to hit nodes directly and it will cache objects./

With aws discovery client using configuration endpoint it always has 0 cache hits but no actual errors.

March 11, 2021 at 12:33 pm #34893

Marko Vasiljevic
Keymaster

Hello Mike,

Thank you for the information.

Does this always happen when logged in or have you checked when logged out from the wp-admin?

Thanks!

March 12, 2021 at 11:30 am #34896

Mike
Guest

I have checked in incognito mode and it is missing cache. Switching back to regular memcached client I can see the hits testing same way.

March 12, 2021 at 11:37 am #34929
Marko Vasiljevic
Keymaster
Hello Mike.

Looking at your website I see
```
Object Caching 419/23626 objects using Memcached
Page Caching using Memcached 
Content Delivery Network via Amazon Web Services: S3: mvpproshop-media.s3.amazonaws.com
Database Caching 2/4883 queries in 14.265 seconds using Memcached (Request-wide modification query)
Served from: localhost @ 2021-03-12 10:06:23 by W3 Total Cache
```
Have you switched to a regular Memcached client and not autodiscovery?
If you check this article you need to Install the Memcached Client
That requires a PHP module amazon-elasticache-cluster-client.so
https://docs.aws.amazon.com/AmazonElastiCache/latest/mem-ug/AutoDiscovery.HowAutoDiscoveryWorks.html
There are the module for:
https://elasticache-downloads.s3.amazonaws.com/ClusterClient/PHP-7.3/latest-64bit
https://elasticache-downloads.s3.amazonaws.com/ClusterClient/PHP-7.2/latest-64bit
https://elasticache-downloads.s3.amazonaws.com/ClusterClient/PHP-7.0/latest-64bit
https://elasticache-downloads.s3.amazonaws.com/ClusterClient/PHP-5.6/latest-64bit
https://elasticache-downloads.s3.amazonaws.com/ClusterClient/PHP-5.5/latest-64bit
https://elasticache-downloads.s3.amazonaws.com/ClusterClient/PHP-5.4/latest-64bit
https://elasticache-downloads.s3.amazonaws.com/ClusterClient/PHP-5.3/latest-64bit
5:15
No 7.4 or 8.0 yet. No 7.1.

Thanks!
March 12, 2021 at 2:26 pm #34932

Mike
Guest

Yes, the production site is using regular memcached client.

I had created a separate environment in AWS for testing and I did downloaded and installed the aws autodiscovery client. This is what I have been discussing. I am pretty sure I have followed all correct procedure for installing it.

The regular PHP memcached client works fine, I haven’t had any issues with this.

AWS autodiscovery client always has 0 cache hits. Your code recognises the autodiscovery client as it allows me to select the autodiscovery checkbox. The test button gives a passing test when I add the configuration endpoint in as address.

There is always 0 cache hits with the AWS autodiscovery client. I have no problems with the regular memcached client.

March 15, 2021 at 8:01 am #34933

Mike
Guest

Sorry, I am just re-reading what you wrote. There is a 7.4 client, it is what I am using but AWS don’t make the link public anymore. To get it you have to go to ElastiCache in AWS and in left menu last option there is a link to download it.

I can email/upload this to you if it helps.

March 15, 2021 at 8:02 am #34969

Mike
Guest

I have realised that with the regular memcached client I am also not getting many hits. It makes ~1600 calls over 10 seconds and gets ~5 hits.

I have contacted AWS and they say they can’t see anything wrong with ElastiCache. I tried upgrading to 16 core elasticache instance but it didn’t make any difference.

I think maybe the issue is with all network memcached calls?

I tried running exact same site with local memcached installed and it get 100% cache hits.

March 15, 2021 at 8:02 am #34989

Mike
Guest

One think I have noticed. If I put exact same site & code locally or on a server with memcached installed locally it will say something like 690/700 object cache hits. When having it on AWS with ElastiCache it will say something like 10/3900 cache hits. Also when memcached on same server it completes in a fraction of a second. With ElastiCache it take 10+ seconds.

AWS are insisting there isn’t anything wrong with ElastiCache but something is obviously wrong.

The site works way better without any cache. As soon as I enable cache the site slows down to a crawl and it can’t handle as much load.

Unfortunately using a single server with memcached locally is not an option for me as during promotions we need to scale up to multiple servers.

Any idea what is wrong?
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