Uninvertible is a safety mechanism to make sure that you don’t _unknowingly_
use a docValues=false
field for faceting/grouping/sorting/function queries. The primary point of
docValues=true is twofold:
1> reduce Java heap requirements by using the OS memory to hold it
2> uninverting can be expensive CPU wise too, although not with just a few
unique values (for each term, read the list of docs that have it and flip a
bit).
It doesn’t really make sense to set it on an index=false field, since
uninverting only happens on
index=true docValues=false. OTOH, I don’t think it would do any harm either.
That said, I frankly
don’t know how that interacts with facet.method=enum.
As far as speed… yeah, you’re in the edge cases. All things being equal,
stuffing these into the
filterCache is the fastest way to facet if you have the memory. I’ve seen very
few installations
where people have that luxury though. Each entry in the filterCache can occupy
maxDoc/8 + some overhead
bytes. If maxDoc is very large, this’ll chew up an enormous amount of memory.
I’m cheating
a bit here since the size might be smaller if only a few docs have any
particular entry then the
size is smaller. But that’s the worst-case you have to allow for ‘cause you
could theoretically hit
the perfect storm where, due to some particular sequence of queries, your
entire filter
cache fills up with entries that size.
You’ll have some overhead to keep the cache at that size, but it sounds like
it’s worth it.
Best,
Erick
> On Jun 17, 2020, at 10:05 AM, James Bodkin <james.bod...@loveholidays.com>
> wrote:
>
> The large majority of the relevant fields have fewer than 20 unique values.
> We have two fields over that with 150 unique values and 5300 unique values
> retrospectively.
> At the moment, our filterCache is configured with a maximum size of 8192.
>
> From the DocValues documentation
> (https://lucene.apache.org/solr/guide/8_3/docvalues.html), it mentions that
> this approach promises to make lookups for faceting, sorting and grouping
> much faster.
> Hence I thought that using DocValues would be better than using Indexed and
> in turn improve our response times and possibly lower memory requirements. It
> sounds like this isn't the case if you are able to allocate enough memory to
> the filterCache.
>
> I haven't yet tried changing the uninvertible setting, I was looking at the
> documentation for this field earlier today.
> Should we be setting uninvertible="false" if docValues="true" regardless of
> whether indexed is true or false?
>
> Kind Regards,
>
> James Bodkin
>
> On 17/06/2020, 14:02, "Michael Gibney" <mich...@michaelgibney.net> wrote:
>
> facet.method=enum works by executing a query (against indexed values)
> for each indexed value in a given field (which, for indexed=false, is
> "no values"). So that explains why facet.method=enum no longer works.
> I was going to suggest that you might not want to set indexed=false on
> the docValues facet fields anyway, since the indexed values are still
> used for facet refinement (assuming your index is distributed).
>
> What's the number of unique values in the relevant fields? If it's low
> enough, setting docValues=false and indexed=true and using
> facet.method=enum (with a sufficiently large filterCache) is
> definitely a viable option, and will almost certainly be faster than
> docValues-based faceting. (As an aside, noting for future reference:
> high-cardinality facets over high-cardinality DocSet domains might be
> able to benefit from a term facet count cache:
> https://issues.apache.org/jira/browse/SOLR-13807)
>
> I think you didn't specifically mention whether you acted on Erick's
> suggestion of setting "uninvertible=false" (I think Erick accidentally
> said "uninvertible=true") to fail fast. I'd also recommend doing that,
> perhaps even above all else -- it shouldn't actually *do* anything,
> but will help ensure that things are behaving as you expect them to!
>
> Michael
>
> On Wed, Jun 17, 2020 at 4:31 AM James Bodkin
> <james.bod...@loveholidays.com> wrote:
>>
>> Thanks, I've implemented some queries that improve the first-hit execution
>> for faceting.
>>
>> Since turning off indexed on those fields, we've noticed that
>> facet.method=enum no longer returns the facets when used.
>> Using facet.method=fc/fcs is significantly slower compared to
>> facet.method=enum for us. Why do these two differences exist?
>>
>> On 16/06/2020, 17:52, "Erick Erickson" <erickerick...@gmail.com> wrote:
>>
>> Ok, I see the disconnect... Necessary parts if the index are read from
>> disk
>> lazily. So your newSearcher or firstSearcher query needs to do whatever
>> operation causes the relevant parts of the index to be read. In this case,
>> probably just facet on all the fields you care about. I'd add sorting too
>> if you sort on different fields.
>>
>> The *:* query without facets or sorting does virtually nothing due to some
>> special handling...
>>
>> On Tue, Jun 16, 2020, 10:48 James Bodkin <james.bod...@loveholidays.com>
>> wrote:
>>
>>> I've been trying to build a query that I can use in newSearcher based off
>>> the information in your previous e-mail. I thought you meant to build a *:*
>>> query as per Query 1 in my previous e-mail but I'm still seeing the
>>> first-hit execution.
>>> Now I'm wondering if you meant to create a *:* query with each of the
>>> fields as part of the fl query parameters or a *:* query with each of the
>>> fields and values as part of the fq query parameters.
>>>
>>> At the moment I've been running these manually as I expected that I would
>>> see the first-execution penalty disappear by the time I got to query 4, as
>>> I thought this would replicate the actions of the newSeacher.
>>> Unfortunately we can't use the autowarm count that is available as part of
>>> the filterCache/filterCache due to the custom deployment mechanism we use
>>> to update our index.
>>>
>>> Kind Regards,
>>>
>>> James Bodkin
>>>
>>> On 16/06/2020, 15:30, "Erick Erickson" <erickerick...@gmail.com> wrote:
>>>
>>> Did you try the autowarming like I mentioned in my previous e-mail?
>>>
>>>> On Jun 16, 2020, at 10:18 AM, James Bodkin <
>>> james.bod...@loveholidays.com> wrote:
>>>>
>>>> We've changed the schema to enable docValues for these fields and
>>> this led to an improvement in the response time. We found a further
>>> improvement by also switching off indexed as these fields are used for
>>> faceting and filtering only.
>>>> Since those changes, we've found that the first-execution for
>>> queries is really noticeable. I thought this would be the filterCache based
>>> on what I saw in NewRelic however it is probably trying to read the
>>> docValues from disk. How can we use the autowarming to improve this?
>>>>
>>>> For example, I've run the following queries in sequence and each
>>> query has a first-execution penalty.
>>>>
>>>> Query 1:
>>>>
>>>> q=*:*
>>>> facet=true
>>>> facet.field=D_DepartureAirport
>>>> facet.field=D_Destination
>>>> facet.limit=-1
>>>> rows=0
>>>>
>>>> Query 2:
>>>>
>>>> q=*:*
>>>> fq=D_DepartureAirport:(2660)
>>>> facet=true
>>>> facet.field=D_Destination
>>>> facet.limit=-1
>>>> rows=0
>>>>
>>>> Query 3:
>>>>
>>>> q=*:*
>>>> fq=D_DepartureAirport:(2661)
>>>> facet=true
>>>> facet.field=D_Destination
>>>> facet.limit=-1
>>>> rows=0
>>>>
>>>> Query 4:
>>>>
>>>> q=*:*
>>>> fq=D_DepartureAirport:(2660+OR+2661)
>>>> facet=true
>>>> facet.field=D_Destination
>>>> facet.limit=-1
>>>> rows=0
>>>>
>>>> We've kept the field type as a string, as the value is mapped by
>>> application that accesses Solr. In the examples above, the values are
>>> mapped to airports and destinations.
>>>> Is it possible to prewarm the above queries without having to define
>>> all the potential filters manually in the auto warming?
>>>>
>>>> At the moment, we update and optimise our index in a different
>>> environment and then copy the index to our production instances by using a
>>> rolling deployment in Kubernetes.
>>>>
>>>> Kind Regards,
>>>>
>>>> James Bodkin
>>>>
>>>> On 12/06/2020, 18:58, "Erick Erickson" <erickerick...@gmail.com>
>>> wrote:
>>>>
>>>> I question whether fiterCache has anything to do with it, I
>>> suspect what’s really happening is that first time you’re reading the
>>> relevant bits from disk into memory. And to double check you should have
>>> docVaues enabled for all these fields. The “uninverting” process can be
>>> very expensive, and docValues bypasses that.
>>>>
>>>> As of Solr 7.6, you can define “uninvertible=true” to your
>>> field(Type) to “fail fast” if Solr needs to uninvert the field.
>>>>
>>>> But that’s an aside. In either case, my claim is that first-time
>>> execution does “something”, either reads the serialized docValues from disk
>>> or uninverts the file on Solr’s heap.
>>>>
>>>> You can have this autowarmed by any combination of
>>>> 1> specifying an autowarm count on your queryResultCache. That’s
>>> hit or miss, as it replays the most recent N queries which may or may not
>>> contain the sorts. That said, specifying 10-20 for autowarm count is
>>> usually a good idea, assuming you’re not committing more than, say, every
>>> 30 seconds. I’d add the same to filterCache too.
>>>>
>>>> 2> specifying a newSearcher or firstSearcher query in
>>> solrconfig.xml. The difference is that newSearcher is fired every time a
>>> commit happens, while firstSearcher is only fired when Solr starts, the
>>> theory being that there’s no cache autowarming available when Solr fist
>>> powers up. Usually, people don’t bother with firstSearcher or just make it
>>> the same as newSearcher. Note that a query doesn’t have to be “real” at
>>> all. You can just add all the facet fields to a *:* query in a single go.
>>>>
>>>> BTW, Trie fields will stay around for a long time even though
>>> deprecated. Or at least until we find something to replace them with that
>>> doesn’t have this penalty, so I’d feel pretty safe using those and they’ll
>>> be more efficient than strings.
>>>>
>>>> Best,
>>>> Erick
>>>>
>>>
>>>
