Implement an improved global search engine

[jeremystretch]

NetBox version

v3.3.4

Feature type

Change to existing functionality

Proposed functionality

This issue is an evolution of the proposal initially outlined in #7016 to improve NetBox's global search functionality, in conjunction with dynamic registration per #8927. This proposal suggests the introduction of a new global search cache, allowing a single database per search query. As this is a fairly complex topic, I've outlined some core areas of focus below. While not a complete implementation plan, it should be sufficient to get started and generate additional discussion.

Caching

Each registered model will declare which of its fields should be cached for search. (This could be done similar to what we currently do with clone_fields and the clone() method.) Fields would be prescribed by name and numeric weighting. For example:

class Book(NetBoxModel):
    title = models.CharField()
    isbn = models.PositiveBigIntegerField()
    author = models.CharField()
    description = models.CharField()

    search_fields = (
        ('title', 200),
        ('isbn', 200),
        ('author', 150),
        ('description', 100),
    )
    
    def cache(self):
        data = []
        for field_name, weight in getattr(self, 'search_fields', []):
            field = self._meta.get_field(field_name)
            value = field.value_from_object(self)
            if field_value not in (None, ''):
                data.append(SearchResult(object=self, field=field_name, value=value, weight=weight))
        return data

On save(), the model's cache() method (name TBD) would be called via a post_save signal handler to generate cache data. A new low-priority background task would then be created to feed this data into the search results table. (Any existing results for the referenced object would first be deleted.) Similarly, search results will be automatically deleted in response to a post_delete signal.

Database Schema

Cached search data from all models would be written to a single table:

Field	Type	Description
timestamp	Datetime	Timestamp of most recent update
object_type	FK(ContentType)	GenericForeignKey component
object_id	Integer	GenericForeignKey component
field	Char	Name of the field/attribute being cached
value	Char	Cached value
weight	Weight	Numeric weight assigned to the field

The object_type and object_id fields would serve a GenericForeignKey named object, which references the cached object.

A populated table might look like this:

timestamp	object_type	object_id	field	value	weight
2022-09-15 1:23	dcim.Device	441	name	akron-rtr1	200
2022-09-15 1:23	dcim.Device	441	serial	A4890274	180
2022-09-15 1:23	dcim.Device	441	asset_tag	H302R8E	180
2022-09-15 1:23	dcim.Device	441	comments	Some text goes here	50
2022-09-15 3:08	dcim.Site	17	name	Akron	200
2022-09-15 3:08	dcim.Site	17	facility	us-oh-akron01	150
2022-09-15 3:08	dcim.Site	17	description	Primary DC for US-East	50
2022-09-15 3:08	dcim.Site	17	physical_address	123 Fake St Akron OH	80

Searching for "akron" would return four rows. We can append .distinct('object_type', 'object_id') to ensure only a single row is returned per object, and we can use .order_by('-weight') to favor the most important result for each object. (We might further order by object type for consistency among objects with identical weights.)

Matching Logic

We could potentially add an exact boolean column to the table, indicating whether each result requires an exact (vs. partial) match. This could be useful for e.g. integer values, where partial matching is typically of little value. For example, we might only want to find exact matches for a device's serial or asset_tag values. Such a query would look like this:

SearchResult.objects.filter(Q(value__iexact='foo') | Q(exact=False, value__icontains='foo'))

It remains to be seen what the performance penalty of this approach looks like. We could also expose exactness as a toggle, enabling the user to search only for exact matches.

Displaying Results

Each matching result will include several attributes:

• The object referenced (with a link)
• The field name on which the match occurred
• The field value, or matched portion of the value

These can be displayed to the user to convey a succinct understanding of why each object was included in the results. Although resolving the object required a GenericForeignKey lookup, this should be automatically reduced via prefetch_related() to a single additional query per type of object returned.

Handling Model Migrations

Some housekeeping will be necessary to delete from the cache search results which reference fields which have been removed from their models. We should be able to hook into the post_migrate signal to detect when migrations have been applied, and bulk delete any entries which reference a field that is no longer referenced under its model's search_fields attribute. A similar approach may be used to detect removed models (e.g. because a plugin was uninstalled).

Considerations

Advantages

• No new PostgreSQL extensions or other dependencies are introduced.
• Both native and plugin models can be registered automatically.
• All results can be returned via a single SQL query, and rendered as a single table.
• An unlimited number of results can be paginated.
• The search logic to be applied can be specified by the user (e.g. exact match vs. partial match vs. "starts with," etc.).
• Employing a background worker ensures that the caching of new results does not impact real-time operations.
• The entire search cache can be rebuilt offline if needed.
• The timestamp column can be compared against an object's last_updated time to identify stale results.

Disadvantages

• We're essentially inventing our own search engine (humble as it may be).
• This approach does not solve for matching by related objects, however it should be noted that this generally not a feature of the current search function, and likely is a reasonable compromise.
• Using a single large table for all results may degrade search performance over time as object counts increase.

Use case

The overall goal here is to provide more robust general purpose search for both core NetBox models as well as those delivered via plugins. Performance, while important, is probably less important than implementing a consistent, flexible search engine.

Database changes

Defined above for clarity

External dependencies

None

[cpmills1975]

I know next to nothing about Redis other than it's an "in memory database" but would holding this table or parts of it in Redis rather than in a PostgreSQL table somehow offer anything?

[ITJamie]

Second on the redis comment, redis tends to be very good at this type of lookup, it would also have the advantage of not growing the "main" databases size (assuming that this new caching table would exist in the same db)

If the decision is made to build a caching table, would it make sense to fork one of djangos existing caching backend modules to leverage this? ( eg removing the MAX_ENTRIES limits )
https://docs.djangoproject.com/en/4.1/topics/cache/#database-caching

[jeremystretch]

Potentially. At this early stage I'm primarily interested in proving viability of the approach, and less concerned with performance. Once we have a working prototype in place using PostgreSQL, we should have a better idea of whether it's feasible to swap in Redis for the cache and what the trade-offs will be.

[cyr0nk0r]

Just curious, rather than inventing your own search .. what is the reluctance to leverage an existing extension, dependency or feature set from another tool to accomplish this?

In the last community call you mentioned this global search and discussed the fact that some users have environments that prevent them from installing additional dependencies. If that is the case, why should the entire user base not be able to take advantage because some environments are more restrictive than others?

Is there any way to make this feature something that can be 'turned on' or 'turned off' either by settings, or the detection of these additional dependencies? If you don't have them, search continues to function the way it does now. If you do, then you get to take advantage of global search?