Database error

Someone does a search every ~20 minutes? That’s a normal Relevanssi database query.

What’s unusual about it is the duplicated taxonomy restriction, but other than that this is a very straightforward Relevanssi search query that should not cause any database problems on a healthy database.

I would recommend asking your hosting provider about this, perhaps they can offer some guidance on this.

That taxonomy restriction does look a bit odd, what kind of tax_query filtering you are using in the search?

You have this appear twice in the problem query:

AND  relevanssi.doc IN (
SELECT DISTINCT(tr.object_id)
FROM wp_term_relationships AS tr
WHERE tr.term_taxonomy_id IN (20,27,103,4329,4341,4395,4446,4450,4451,4452,4483,4484,4539,4569,4778,6067,6547,6664,6796,3184,4444,4445,4775,4912,7618,8708,4448,4449,4896,7899,8757,8758,4914,4543,7552,8815,6665,6667,8294,8295)
)

This adds a restriction that the search results must be within these 40 categories (or other taxonomies). This restriction appears twice. Why? Is it something that is done on purpose? Does this appear in normal searches that don’t exhaust the MySQL server?

If you install Query Monitor, you can use it to look at the Relevanssi query. If you check a working Relevanssi query with the Query Monitor, does the same taxonomy restriction appear there as well? If it does, then that’s not the problem, but if it doesn’t, that looks like the problem.

Your hosting provider should be able to help you figure out if these problem queries are related to specific action on your site. If these problem queries happen at certain intervals, perhaps there’s some bot that visits your site doing a problematic query that causes this? That’s one possibility.

Since it’s Google Bot, that should be easy: Google Bot listens to robots.txt, so if you tell it in your robots.txt that your search pages are out of bounds, it should not go there. That would be good, because Google isn’t supposed to index your search result pages in the first place.

You can look at the server access logs to see the exact URL the Google Bot is visiting: the taxonomy restrictions should appear in that URL. You can then probably block access to that URL completely.

You can also try adding this to your theme functions.php:

add_filter( 'relevanssi_search_ok', 'rlv_stop_google_bot' );
function rlv_stop_google_bot( $ok ) {
  if ( isset( $_SERVER['HTTP_USER_AGENT'] ) ) {
    if ( false !== stristr( $_SERVER['HTTP_USER_AGENT'], 'google' ) ) {
      $ok = false;
    }
    if ( false !== stristr( $_SERVER['HTTP_USER_AGENT'], 'bot' ) ) {
      $ok = false;
    }
  }
  return $ok;
}

This will look for the user agent value from the searcher and if it contains “google” or “bot”, it will stop Relevanssi from running.