[jira] [Comment Edited] (SOLR-16594) improve eDismax strategy for generating a term-centric query

["Rudi Seitz (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-16594?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17650967#comment-17650967 ] 

Rudi Seitz edited comment on SOLR-16594 at 3/15/23 4:23 PM:
------------------------------------------------------------

This is a rough outline of the code changes that might be needed to implement the proposal in this ticket:
 # Add an int startOffset to org.apache.lucene.index.Term. Alternatively, create a TermWithOffset subclass of Term
 # Update org.apache.lucene.util.QueryBuilder so that so that createFieldQuery() returns a Query that contains Terms with the startOffset properly set. This is the place where we iterate through the token stream and have access to the offsets so we can store them on the generated Terms.
 # Update org.apache.solr.search.ExtendedDismaxQParser so that getAliasedMultiTermQuery() builds clauses based on startOffset instead of the current approach of calling allSameQueryStructure() and then doing "{color:#808080}Make a dismax query for each clause position in the boolean per-field queries"{color}

 

{color:#808080}UPDATE: 3/15/2023{color}

{color:#808080}Instead of updating the Lucene Term class I found it was possible store the startOffset on the Query objects generated during parsing. This eliminates storage overhead and allows the changes to be made entirely inside the solr codebase.{color}


was (Author: JIRAUSER297477):
This is a rough outline of the code changes that might be needed to implement the proposal in this ticket:
 # Add an int startOffset to org.apache.lucene.index.Term. Alternatively, create a TermWithOffset subclass of Term
 # Update org.apache.lucene.util.QueryBuilder so that so that createFieldQuery() returns a Query that contains Terms with the startOffset properly set. This is the place where we iterate through the token stream and have access to the offsets so we can store them on the generated Terms.
 # Update org.apache.solr.search.ExtendedDismaxQParser so that getAliasedMultiTermQuery() builds clauses based on startOffset instead of the current approach of calling allSameQueryStructure() and then doing "{color:#808080}Make a dismax query for each clause position in the boolean per-field queries"{color}

> improve eDismax strategy for generating a term-centric query
> ------------------------------------------------------------
>
>                 Key: SOLR-16594
>                 URL: https://issues.apache.org/jira/browse/SOLR-16594
>             Project: Solr
>          Issue Type: Improvement
>          Components: query parsers
>            Reporter: Rudi Seitz
>            Priority: Major
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> When parsing a multi-term query that spans multiple fields, edismax attempts to generate a term-centric query structure
>  
> sometimes switches from a "term-centric" to a "field-centric" approach. This creates inconsistent semantics for the {{mm}} or "min should match" parameter and may have an impact on scoring. The goal of this ticket is to improve the approach that edismax uses for generating term-centric queries so that edismax would less frequently "give up" and resort to the field-centric approach. Specifically, we propose that edismax should create a dismax query for each distinct startOffset found among the tokens emitted by the field analyzers. Since the relevant code in edismax works with Query objects that contain Terms, and since Terms do not hold the startOffset of the Token from which Term was derived, some plumbing work would need to be done to make the startOffsets available to edismax.
>  
> BACKGROUND:
>  
> If a user searches for "foo bar" with {{{}qf=f1 f2{}}}, a field-centric interpretation of the query would contain a clause for each field:
> {{  (f1:foo f1:bar) (f2:foo f2:bar)}}
> while a term-centric interpretation would contain a clause for each term:
> {{  (f1:foo f2:foo) (f1:bar f2:bar)}}
> The challenge in generating a term-centric query is that we need to take the tokens that emerge from each field's analysis chain and group them according to the terms in the user's original query. However, the tokens that emerge from an analysis chain do not store a reference to their corresponding input terms. For example, if we pass "foo bar" through an ngram analyzer we would get a token stream containing "f", "fo", "foo", "b", "ba", "bar". While it may be obvious to a human that "f", "fo", and "foo" all come from the "foo" input term, and that "b", "ba", and "bar" come from the "bar" input term, there is not always an easy way for edismax to see this connection. When {{{}sow=true{}}}, edismax passes each whitespace-separated term through each analysis chain separately, and therefore edismax "knows" that the output tokens from any given analysis chain are all derived from the single input term that was passed into that chain. However, when {{{}sow=false{}}}, edismax passes the entire multi-term query through each analysis chain as a whole, resulting in multiple output tokens that are not "connected" to their source term.
> Edismax still tries to generate a term-centric query when {{sow=false}} by first generating a boolean query for each field, and then checking whether all of these per-field queries have the same structure. The structure will generally be uniform if each analysis chain emits the same number of tokens for the given input. If one chain has a synonym filter and another doesn’t, this uniformity may depend on whether a synonym rule happened to match a term in the user's input.
> Assuming the per-field boolean queries _do_ have the same structure, edismax reorganizes them into a new boolean query. The new query contains a dismax for each clause position in the original queries. If the original queries are {{(f1:foo f1:bar)}} and {{(f2:foo f2:bar)}} we can see they have two clauses each, so we would get a dismax containing all the first position clauses {{(f1:foo f1:bar)}} and another dismax containing all the second position clauses {{{}(f2:foo f2:bar){}}}.
> We can see that edismax is using clause position as a heuristic to reorganize the per-field boolean queries into per-term ones, even though it doesn't know for sure which clauses inside those per-field boolean queries are related to which input terms. We propose that a better way of reorganizing the per-field boolean queries is to create a dismax for each distinct startOffset seen among the tokens in the token streams emitted by each field analyzer. The startOffset of a token (rather, a PackedTokenAttributeImpl) is "the position of the first character corresponding to this token in the source text".
> We propose that startOffset is a resonable way of matching output tokens up with the input terms that gave rise to them. For example, if we pass "foo bar" through an ngram analysis chain we see that the foo-related tokens all have startOffset=0 while the bar-related tokens all have startOffset=4. Likewise, tokens that are generated via synonym expansion have a startOffset that points to the beginning of the matching input term. For example, if the query "GB" generates "GB gib gigabyte gigabytes" via synonym expansion, all of those four tokens would have startOffset=0.
> Here's an example of how the proposed edismax logic would work. Let's say a user searches for "foo bar" across two fields, f1 and f2, where f1 uses a standard text analysis chain while f2 generates ngrams. We would get field-centric queries {{(f1:foo f1:bar)}} and ({{{}f2:f f2:fo f2:foo f2:b f2:ba f2:bar){}}}. Edismax's "all same query structure" check would fail here, but if we look for the unique startOffsets seen among all the tokens we would find offsets 0 and 4. We could then generate one clause for all the startOffset=0 tokens {{(f1:foo f2:f f2:fo f2:foo)}} and another for all the startOffset=4 tokens: {{{}(f1:bar f2:b f2:ba f2:bar){}}}. This would effectively give us a "term-centric" query with consistent mm and scoring semantics, even though the analysis chains are not "compatible."
> As mentioned, there would be significant plumbing needed to make startOffsets available to edismax in the code where the per-field queries are converted into per-term queries. Modifications would possibly be needed in both the Solr and Lucene repos. This ticket is logged in hopes of gathering feedback about whether this is a worthwhile/viable approach to pursue further.
>  
> Related tickets:
> https://issues.apache.org/jira/browse/SOLR-12779
> https://issues.apache.org/jira/browse/SOLR-15407
>  
> Related blog entries:
> [https://opensourceconnections.com/blog/2018/02/20/edismax-and-multiterm-synonyms-oddities]
> [https://sease.io/2021/05/apache-solr-sow-parameter-split-on-whitespace-and-multi-field-full-text-search.html]
>  



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