core_output_cache

[Square Wheels]

What is this table used for?  It's wiping out one of my sites at 4+GB.

[Martin A.]

It's the ... output ... cache... 

It is used to cache the output for guests in order to reduce load time and server usage for guest traffic.

Quote

When enabled, the entire page output will be cached so if more than one guest is viewing the site, each page only needs to be generated once which can significantly decrease the resource usage of your site if you have lots of guests online at the same time.
The longer you cache pages for, the less often the cache will need to be refreshed (so less resources will be used) but the longer it will take for your site to be updated with the latest content. When a cached page is being shown, view counters also won't be updated.
If your site rarely has many guests online at the same time, it may take more resources to store the cache than is saved by it and so it may be better to disable it.
If you have a caching method configured that will be used, otherwise the cache is stored in the database.

The default time to store the cache is 30 seconds. If you've increased this the size of that table will drastically increase. If you're low on space you may consider turning it off.

Search for "guest cache" in the ACP search bar to find the setting.

Edited November 17, 2019 by Martin A.

[Square Wheels]

Thank you.  It's currently set to 30 seconds.

Yesterday that table was over 4GB, as of right now, it's at 177MB.  So far this month I've user about 45GB of bandwidth.  It's a small site.  https://www.pathlabtalk.com/forum/

Is it normal for that table to vary so wildly?

Thank you again

[Martin A.]

The size will of course vary with guest traffic. I guess you'll see an increase when a crawler is accessing your site. 

I've never monitored the size of that table, so can't tell you if what you're seeing is normal.

[bfarber]

Yes, it's impossible to tell you how big it "should" be. There are several factors:

• How long you cache guest pages for (you already said 30 seconds).
• How big your site is - is there a lot to cache?
• How much guest traffic you get - if you don't allow guests to access your site, that page will stay small by the nature of your traffic patterns.
• If you don't get much activity in general and aren't using cron, the task that clears the table may not be running enough.

You get the idea. Note that you can also store guest cached pages in Redis or in a remote MySQL database, or turn the feature off entirely. That said, it can improve performance quite dramatically for sites with any significant amount of guest traffic, especially during "surges" in traffic.

[maddog107_merged]

Mine is 

713G ibf_core_output_cache.ibd

 

Just in case someone is wondering how to fix. If you are using Innodb and a file per tablespace is turned on  you can do

 

MariaDB [bellazon_v4]> optimize table ibf_core_output_cache;
+-----------------------------------+----------+----------+-------------------------------------------------------------------+
| Table                             | Op       | Msg_type | Msg_text                                                          |
+-----------------------------------+----------+----------+-------------------------------------------------------------------+
| abc_v4.ibf_core_output_cache | optimize | note     | Table does not support optimize, doing recreate + analyze instead |
| abc_v4.ibf_core_output_cache | optimize | status   | OK                                                                |
+-----------------------------------+----------+----------+-------------------------------------------------------------------+
2 rows in set (12.177 sec)

 

It dropped down to 340 MB!!!!!

340M Dec  8 10:57 ibf_core_output_cache.ibd

 

 

 

Edited December 8, 2020 by maddog107_merged