# FAQ & Troubleshooting

When in doubt try flushing the cache, you'd be surprised how often this resolves issues. Welcome to WordPress ✌️

- [HELP! My site is down!1!!11!!11](#help-my-site-is-down11111)
- [Plugin is incompatible with OtherPlugin](#plugin-is-incompatible-with-otherplugin)
- [How can I ignore a cache group?](#how-can-i-ignore-a-cache-group)
- [How can I exclude a page from the cache?](#how-can-i-exclude-a-page-from-the-cache)
- [Status: <code>Not connected</code>](#status-not-connected)
- [<code>connection timed out</code> and <code>read error on connection</code>](#connection-timed-out-and-read-error-on-connection)
- [My site is getting redirected another domain](#my-site-is-getting-redirected-another-domain)
- [Are transients stored in Redis?](#are-transients-stored-in-redis)
- [I'm getting <code>404</code> errors](#im-getting-404-errors)
- [WordPress is slower with Redis Object Cache enabled](#wordpress-is-slower-with-redis-object-cache-enabled)
- [<code>NOAUTH Authentication required</code>](#noauth-authentication-required)
- [<code>Allowed memory size of 1337 bytes exhausted</code>](#allowed-memory-size-of-1337-bytes-exhausted)
- [<code>OOM command not allowed</code>](#oom-command-not-allowed)
- [<code>Flushing the cache causes timeout</code>](#flushing-the-cache-causes-timeout)
- [Unable to flush the cache](#unable-to-flush-the-cache)
- [Cache is flushed constantly](#cache-is-flushed-constantly)
- [Flushing the cache regularly](#flushing-the-cache-regularly)
- [How can I uninstall the cache?](#how-can-i-uninstall-the-cache)

## HELP! My site is down!1!!11!!11

The easiest way to to disable Redis on your site is deleting the `wp-content/object-cache.php` drop-in file. Alternatively, you can set the `WP_REDIS_DISABLED` constant to `true` to bypass loading it.

## Plugin is incompatible with OtherPlugin

Unfortunately many plugin authors don't bother testing their plugins with a persistent object cache. If you’re experiencing a compatibility issue with another plugin in combination with Redis Object Cache, please contact the support team of the **other plugin** regarding the issue.

This plugin is **not the issue**, it's just providing WordPress with `wp_cache_*()` functions for persistent caching.

## How can I ignore a cache group?

Some plugins don’t play nicely with a persistent object cache in WordPress and either cause stale cache data, or straight up break functionality. In such scenarios you might be able to exclude the faulty plugin's cache groups:

```php
define( 'WP_REDIS_IGNORED_GROUPS', [
    'wpseo', // just an example
] );
```

## How can I exclude a page from the cache?

Object caching caches only **objects**, not **pages**. You cannot exclude a page from using the object cache, because object caching is not URL-centric. You also cannot exclude the WordPress admin dashboard from using object caching, because then you risk the cache going stale and even loosing data.

If you’re experiencing a compatibility issue with another plugin in combination with Redis Object Cache, please contact the support team of the plugin regarding the issue and ask them to ensure it's compatible with persistent object cache backends, like Redis.

## Status: <code>Not connected</code>

This means that either [Redis Server](https://redis.io) is not installed and running, or the plugin is not configured correctly. 
    
First, make sure you followed the [installation instructions](https://github.com/rhubarbgroup/redis-cache/blob/develop/INSTALL.md) and that Redis Server is up and running:

```bash
redis-cli PING

# or specify a custom host/port
redis-cli -h 127.0.0.1 -p 6379 PING
```

If Redis Server is not installed and running, follow the installation instructions, or ask your hosting company for assistance.

Next, make sure confirm the `wp-config.php` file contains the correct `WP_REDIS_*` constants and configuration constants are defined high up in the `wp-config.php` **above the lines**:

```php
/* That's all, stop editing! Happy publishing. */
require_once(ABSPATH . 'wp-settings.php');
```

If you moved all constants above those lines and the plugin still shows `Not Connected`, double check your [connection options](https://github.com/rhubarbgroup/redis-cache#connections), or ask your hosting provider for assistance.

## <code>connection timed out</code> and <code>read error on connection</code>
If the error occurs rarely, ignore it, Redis Server is having a hiccup. If it persists, read the answer to "Status: <code>Not connected</code>".

## My site is getting redirected another domain

That happens when the same `WP_REDIS_DATABASE` index is used for multiple WordPress installations. You **MUST** set a separate `WP_REDIS_DATABASE` and `WP_REDIS_PREFIX` for each domain to avoid data collision.

Once your site is being redirected, you **MUST** flush the entire Redis Server using the `FLUSHALL` command to recover from this error:

```bash
redis-cli -h 127.0.01 -p 6379 FLUSHALL
```

## Are transients stored in Redis?

Yes. The WordPress [Transients API](https://developer.wordpress.org/apis/transients/) will use Redis to store transients and not the `options` table.

After enabling Redis Object Cache, consider deleting all database transients:

```bash
wp transient delete-all
```

```sql
DELETE FROM `wp_options`
WHERE `option_name` LIKE '_transient_%'
OR `option_name` LIKE '_site_transient_%';
```

## I'm getting <code>404</code> errors

This may be an issue with WordPress 6.1's [query caching](https://make.wordpress.org/core/2022/10/07/improvements-to-wp_query-performance-in-6-1/) feature, which you can disable by creating your own [Must Use Plugin](https://wordpress.org/documentation/article/must-use-plugins/) containing this snippet:

```php
add_action( 'parse_query', function ( $wp_query ) {
    $wp_query->query_vars[ 'cache_results' ] = false;
} );
```

## WordPress is slower with Redis Object Cache enabled

This should never always means **something is broken**.

1. Does the plugin show "Connected"?
2. Is Redis Server responding too slowly? Run `redis-cli --latency-history` to find out.
3. Is Redis Server maxing out it's RAM or CPU?

## <code>NOAUTH Authentication required</code>

You either need to add the `WP_REDIS_PASSWORD` constant to your `wp-config.php` file, or move the constant above higher up in your `wp-config.php` file, above these lines:

```php
/* That's all, stop editing! Happy publishing. */
require_once(ABSPATH . 'wp-settings.php');
```

## <code>Allowed memory size of 1337 bytes exhausted</code>

This can happen when using a persistent object cache. Increase PHP's memory limit.

- <https://wordpress.org/documentation/article/common-wordpress-errors/#allowed-memory-size-exhausted>
- <https://woocommerce.com/document/increasing-the-wordpress-memory-limit/>

## <code>OOM command not allowed</code>

This can happen when Redis Server runs out of memory and no `maxmemory-policy` was set in the `redis.conf`.

- <https://aws.amazon.com/premiumsupport/knowledge-center/oom-command-not-allowed-redis/>

Alternatively, you can set the `WP_REDIS_MAXTTL` constant to something relatively low (like `3600` seconds) and flush the cache.

## <code>Flushing the cache causes timeout</code>

This can happen when the dataset in Redis Server is quite large. Consider increasing `WP_REDIS_READ_TIMEOUT` and `WP_REDIS_FLUSH_TIMEOUT` to 5-10 seconds.

Alternatively, starting with Redis 6.2, setting the `lazyfree-lazy-user-flush` in the `redis.conf` configuration directive to `yes` changes the default flush mode to be asynchronous.

## Unable to flush the cache

If your site is unreachable, you can flush the cache without access to the WordPress dashboard. 

Try running `wp cache flush`, or using `redis-cli` directly:

```bash
redis-cli -h 127.0.01 -p 6379 FLUSHALL
```

Alternatively, you can use a desktop client like [Medis](https://getmedis.com) or [RedisInsight](https://redis.com/redis-enterprise/redis-insight/) to connect to your Redis Server and flush it by executing `FLUSHALL`.

## Cache is flushed constantly

If you don't see metrics building up, or your site is not getting faster, you might have an active plugin that flushes the object cache frequently. To diagnose this issue you can use the following snippet to find the source of the cache flush:

```php
add_action( 'redis_object_cache_flush', function( $results ) {
    ob_start();
    echo date( 'c' ) . PHP_EOL;
    var_dump( $results );
    debug_print_backtrace();
    error_log( ob_get_clean(), 3, ABSPATH . '/redis-cache-flush.log' );
}, 10, 5 );
```

Once you found the plugin responsible by checking `redis-cache-flush.log`, you can contact the plugin author(s) and reporting the issue.

## Flushing the cache regularly

It's considered a bad practise to flush the frequently, but sometimes 3rd party plugins and themes just don't play nice with persistent object caches. When the plugin/theme authors refuse to fix their code you can use [WP Cron](https://developer.wordpress.org/plugins/cron/) to flush the Redis object cache frequently.

```php
if ( ! wp_next_scheduled( 'flush_redis_cache' ) ) {
    wp_schedule_event( time(), 'hourly', 'flush_redis_cache' );
}

add_action( 'flush_redis_cache', 'wp_cache_flush' );
```

## How can I uninstall the cache?

Before [uninstalling the plugin](https://wordpress.org/documentation/article/manage-plugins/#uninstalling-plugins-1), be sure to disable the cache via `WordPress -> Settings -> Redis`.

If you already removed the plugin before doing so, you can delete the `object-cache.php` file in your `/wp-content/` directly.