Hi Greg, Yes, in future we consider to implement our own shard management with entire index split and merge operations, so for now we just wanted to make sure that Taxonomy won't make it too complicated. In fact, recently I found the TaxonomyMergeUtils, which is doing just that - merging the main and taxonomy index pairs. Looks pretty straightforward, although the complexity is a bit hidden there: https://github.com/apache/lucene/blob/main/lucene/facet/src/java/org/apache/lucene/facet/taxonomy/TaxonomyMergeUtils.java
It's definitely slower than regular index merge because of the additional work to translate the ordinals, but anyway it's much better than full re-index. I would appreciate any advice if someone used this approach. -- Thank you, Alex On Fri, Apr 30, 2021 at 3:53 PM Greg Miller <gsmil...@gmail.com> wrote: > Interesting Alex. So for your "merge" case, are you suggesting you > would have a different taxonomy index for each segment and would need > to merge those? I could be completely mistaken (I'm not nearly as > familiar with the indexing side of things), but I thought Lucene > maintains one single taxonomy index regardless of how many shards > there are. It should be append-only where new ordinals are created > when they're first seen, and then stay stable through merges. Or am I > misunderstanding your use-case and you're actually doing some shard > management on top of what Lucene is doing? > > Cheers, > -Greg > > On Thu, Apr 29, 2021 at 2:48 PM Alexander Lukyanchikov > <alexanderlukyanchi...@gmail.com> wrote: > > > > Hi Greg, Matt, > > Thank you for the responses, it's very helpful and great to hear that > > Taxonomy is successfully used for large scale products! > > > > Our biggest concern with it right now is future complications related to > > index split and merge, which we are most likely going to use to implement > > sharding and rebalancing. While split should not be too complicated > > (pre-split taxonomy works for the divided parts, and we can build an > > optimized taxonomy without unused categories in background for each new > > index), the merge seems to be challenging and probably involves tricky > > logic to translate ordinals from respective taxonomies, also taking into > > account parent-child order guarantees for hierarchical categories. > > > > I wonder if anyone implemented something similar, or have any thoughts or > > ideas about that? > > > > -- > > Regards, > > Alex > > > > > > On Thu, Apr 29, 2021 at 6:08 AM Greg Miller <gsmil...@gmail.com> wrote: > > > > > Hi Alex- > > > > > > Amazon's product search engine is built on top of Lucene, which is a > > > fairly large-scale application (w.r.t. both index size, traffic and > > > use-case complexity). We have found taxonomy-based faceting to work > > > well for us generally, and haven't needed to do much to optimize > > > beyond what's already there. As you can imagine, with Amazon's catalog > > > being quite broad, we have a large number of unique facets available > > > for customers to use, which means a single facet-field storing all > > > dimensions can have high cardinality (as is the case by default with > > > taxonomy facets). This is an area where we have experimented a little > > > bit (e.g., "sharding" facets into separate fields to lower cardinality > > > of counting at query-time), but we tend to find Lucene works well > > > "as-is" for the most part in this sapce. The last bit I'll mention > > > here is that, for fields that are numeric and low-cardinality in > > > nature, LUCENE-7927 > > > (https://issues.apache.org/jira/browse/LUCENE-7927) added the ability > > > to count these cases a bit more efficiently than trying to apply a > > > taxonomy-based approach. > > > > > > Happy faceting! > > > > > > Cheers, > > > -Greg > > > > > > On Thu, Apr 29, 2021 at 5:09 AM Matt Davis <kryptonics...@gmail.com> > > > wrote: > > > > > > > > Alex, > > > > > > > > We did consider trying to optimize Taxonomy indexing performance but > we > > > > never really got around to it. The sidecar index is annoying to deal > > > with > > > > and we have had occasional issues with it. Zulia has sharding > > > implemented. > > > > The main issue here is not the taxonomy but rather just getting exact > > > > counts with returning all facets values. We chose to implement a > method > > > > similar to elastic search ( > > > > > > > > https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-bucket-terms-aggregation.html#_per_bucket_document_count_error > > > ). > > > > For replication we plan to use native Lucene index replication built > into > > > > lucene. The framework is currently there for routing queries and > such > > > but > > > > the actual copying of the index has not been implemented yet so I > can't > > > > speak to that. Hope this helps some. > > > > > > > > Thanks, > > > > Matt > > > > > > > > > > > > On Wed, Apr 28, 2021 at 5:48 PM Alexander Lukyanchikov < > > > > alexanderlukyanchi...@gmail.com> wrote: > > > > > > > > > Hi Matt, > > > > > It's very interesting, thanks for the response! Did you have any > issues > > > > > with Taxonomy indexing performance, or maybe tried to optimize it > > > somehow? > > > > > Also, any problems maintaining a sidecar index or experience > building a > > > > > distributed system around it with sharding/rebalancing? > > > > > > > > > > -- > > > > > Regards, > > > > > Alex > > > > > > > > > > > > > > > On Wed, Apr 28, 2021 at 11:18 AM Matt Davis < > kryptonics...@gmail.com> > > > > > wrote: > > > > > > > > > > > Alex, > > > > > > > > > > > > With our lucene based implementation of Zulia ( > > > > > > https://github.com/zuliaio/zuliasearch) we have went back and > > > forth. We > > > > > > started with Taxonomy and switched and then switched back to > > > taxonomy. > > > > > In > > > > > > our experience the Taxonomy based approach is more scalable and > > > > > > performant. We do large searches (sometimes returning millions > of > > > > > > results) with about 20 facets being run with some high > cardinality > > > > > facets. > > > > > > A small dataset version of the tool that is backed by zulia we > > > released > > > > > for > > > > > > covid can be found here ( > > > > > > > > > > > > > > > > > > > > > https://icite.od.nih.gov/covid19/search/#search:searchId=6089a5b7218c6902d422e907 > > > > > > ). > > > > > > If you click on the facet tab you can see how we use facets. I > > > believe > > > > > the > > > > > > use case might largely drive the choice. > > > > > > > > > > > > Thanks, > > > > > > Matt > > > > > > > > > > > > On Wed, Apr 28, 2021 at 1:26 PM Alexander Lukyanchikov < > > > > > > alexanderlukyanchi...@gmail.com> wrote: > > > > > > > > > > > > > Hello everyone, > > > > > > > > > > > > > > We are trying to choose between Taxonomy and > > > > > SortedSetDocValuesFacetField > > > > > > > implementations for faceted search, and based on available > > > information > > > > > > and > > > > > > > our quick tests, the difference is the following - > > > > > > > > > > > > > > - Taxonomy is faster at query time (on our test workload, the > > > > > difference > > > > > > > sometimes is higher than documented 25%). Also SortedSet adds > > > latency > > > > > to > > > > > > an > > > > > > > NRT refresh. > > > > > > > - Taxonomy is slower at index time, and unlike SortedSet > > > > > implementation, > > > > > > it > > > > > > > does not scale as good with more than 4 threads (a lot of > > > contention at > > > > > > > DirectoryTaxonomyWriter#addCategory() and > > > UTF8TaxonomyWriterCache.get() > > > > > > > synchronized blocks) > > > > > > > - SortedSet does not support hierarchical queries > > > > > > > - SortedSet does not require a sidecar index > > > > > > > - Tie-break differences for labels with the same count > > > > > > > > > > > > > > Am I missing something, or that’s everything we should take > into > > > > > account > > > > > > as > > > > > > > of today? > > > > > > > > > > > > > > I know that Solr and ES use their own faceting for historical > > > reasons, > > > > > > but > > > > > > > are there any other large Lucene-based products, which have > chosen > > > one > > > > > > > implementation over another? Do we know why? > > > > > > > Any insight on less known trade-offs and production experience > is > > > > > greatly > > > > > > > appreciated! > > > > > > > > > > > > > > -- > > > > > > > Thank you, > > > > > > > Alex > > > > > > > > > > > > > > > > > > > > > > > > --------------------------------------------------------------------- > > > To unsubscribe, e-mail: java-user-unsubscr...@lucene.apache.org > > > For additional commands, e-mail: java-user-h...@lucene.apache.org > > > > > > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: java-user-unsubscr...@lucene.apache.org > For additional commands, e-mail: java-user-h...@lucene.apache.org > >
