[Fixed]-Django haystack whoosh super slow

You say in the question:

I then updated my search view to prefetch relations […]

The code you present, though, does not use QuerySet.prefetch_related for most of them. Instead, your sample code uses QuerySet.select_related for most of them; this does not pre-fetch the objects.

The documentation for each of those methods is extensive and can help to decide which is correct for your case.

In particular, the QuerySet.prefetch_related documentation says:

select_related works by creating an SQL join and including the fields of the related object in the SELECT statement. For this reason, select_related gets the related objects in the same database query. However, to avoid the much larger result set that would result from joining across a ‘many’ relationship, select_related is limited to single-valued relationships – foreign key and one-to-one.

prefetch_related, on the other hand, does a separate lookup for each relationship, and does the ‘joining’ in Python. This allows it to prefetch many-to-many and many-to-one objects, which cannot be done using select_related, in addition to the foreign key and one-to-one relationships that are supported by select_related. It also supports prefetching of GenericRelation and GenericForeignKey, however, it must be restricted to a h*m*geneous set of results. For example, prefetching objects referenced by a GenericForeignKey is only supported if the query is restricted to one ContentType.

Try adding

HAYSTACK_LIMIT_TO_REGISTERED_MODELS = False

to your settings.py. As per the docks,

‘If your search index is never used for anything other than the models registered with Haystack, you can turn this off and get a small to moderate performance boost.’

It knocked 3-4 seconds off for my project