[BUG/PERF] `LIKE` and relevance-function pushdown gaps on Calcite engine

Inizia da opensearch/src/main/java/org/opensearch/sql/opensearch/request/PredicateAnalyzer.java:1343-1361 e dal fallback a :239-249, quindi esamina la lacuna di pushdown tracciata in #3668. Usa la matrice di riproduzione per verificare il rifiuto anticipato delle funzioni di rilevanza delle colonne derivate e il rewrite LIKE protetto per i campi di testo. Aggiorna docs/user/ppl/cmd/where.md con i casi di prestazioni documentati e il comportamento dell'impostazione.

Test data

5000 docs, each with three identical fields holding a string like:

logtype=ws:access http_status=200 uri="..." user_agent="Go-http-client/1.1" ...

• body_text (text)
• body_keyword (keyword)
• body_multi (text + .keyword subfield)
• lt = rex-extracted from body (VARCHAR)

logtype is randomly drawn from {ws:access, ws:error, app:debug, app:info}.

Ground truth

• 1271 docs contain ws:access as a substring
• 993 docs contain Go-http-client as a substring

Correctness legend

• OK — result matches the operator's defined behavior given the field type.
• WRONG — result deviates from the operator's defined behavior.
• FAIL — query errors out at runtime.

Note: rows that return 0 hits can still be OK when the operator is doing what it's defined to do. For example, LIKE(body_text, "ws:access") (no wildcards) means strict equality — long body string ≠ short literal → 0 hits is correct. match(body_keyword, "ws:access") does whole-value term matching against the keyword field — body value ≠ literal → 0 hits is correct.

Probe 1: ws:access

query	hits	correctness	dsl
LIKE(body_text, "ws:access")	0	OK	SCRIPT[ILIKE]
LIKE(body_text, "%ws:access%")	1271	OK	SCRIPT[ILIKE]
match(body_text, "ws:access")	1271	OK	match
match_phrase(body_text, "ws:access")	1271	OK	match_phrase
LIKE(body_keyword, "ws:access")	0	OK	wildcard case_insensitive=true
LIKE(body_keyword, "%ws:access%")	1271	OK	wildcard case_insensitive=true
match(body_keyword, "ws:access")	0	OK	match
match_phrase(body_keyword, "ws:access")	0	OK	match_phrase
body_keyword = "ws:access"	0	OK	term
LIKE(body_multi, "ws:access")	0	OK	wildcard(.keyword) case_insensitive=true
LIKE(body_multi, "%ws:access%")	1271	OK	wildcard(.keyword) case_insensitive=true
match(body_multi, "ws:access")	1271	OK	match
match_phrase(body_multi, "ws:access")	1271	OK	match_phrase
LIKE(lt, "ws:access")	1271	OK	SCRIPT[ILIKE]
LIKE(lt, "%ws:access%")	1271	OK	SCRIPT[ILIKE]
match(lt, "ws:access")	ERR	FAIL	SCRIPT[match] (rejected at runtime)
match_phrase(lt, "ws:access")	ERR	FAIL	SCRIPT[match_phrase] (rejected at runtime)
lt = "ws:access"	1271	OK	SCRIPT[=]

16 of 18 cells produce a result. Two cells hard-fail at runtime.

Issues identified from the matrix

Issue 1 — match / match_phrase behave inconsistently across field types

The same match / match_phrase operator produces three different outcomes depending on the field's type:

field type	behavior	example
text	works as expected — token / phrase match against the inverted index	match(body_text, "ws:access") → 1271
text + .keyword	works as expected on the text path	match(body_multi, "ws:access") → 1271
keyword	whole-value matching — typically returns 0 when the keyword value is a long string	match(body_keyword, "ws:access") → 0
derived (rex/eval)	hard error: Relevance search query functions are only supported when they are pushed down	match(lt, "ws:access") → 500

The keyword case is Lucene-correct but easy to mistake for "no matches found." The derived-column case is a hard runtime failure: the planner emits a SCRIPT[match] clause; the script engine rejects relevance functions at compile time; the query never executes.

This is especially painful because "use match_phrase instead of LIKE" is the natural workaround for the perf issue below — but that workaround fails the moment a user touches a rex-extracted column.

Cross-reference: #3668 — relevance functions need pushdown plumbing in Calcite that doesn't exist yet for derived columns.

Proposal — Issue 1

1. Reject early, not at runtime. When the planner sees match / match_phrase against a non-pushdownable column (Calcite-derived, no underlying field), fail fast at planning time with a clear error message naming the column and suggesting alternatives. Don't generate a SCRIPT[match] clause that's guaranteed to fail server-side.
2. Document the keyword-field case in PPL relevance-function docs: match / match_phrase on a keyword field perform whole-value term matching, not substring/phrase. Common alternatives: use a text analyzer, query the .keyword subfield only with =/LIKE %X%, or restructure the data.
3. Track in #3668 — when relevance-function pushdown extends to derived columns, the hard-fail case becomes a script-path execution.

---

Issue 2 — LIKE on a pure text field is a script query (perf)

Two text-field rows emit SCRIPT[ILIKE] instead of a native Lucene query:

• LIKE(body_text, "ws:access")
• LIKE(body_text, "%ws:access%")

Both produce correct results, but as a Painless ScriptQuery that scans _source per document. The same intent expressed as match_phrase(body_text, "ws:access") returns the same 1271 hits via a native Lucene query. Adding a .keyword subfield to the mapping (the body_multi rows) automatically routes LIKE through wildcard_query against the subfield — fast.

(The rex-extracted lt rows also emit SCRIPT[ILIKE], but those are inherently script because lt is a Calcite-derived column not backed by an index — same root cause as Issue 1.)

Root cause — opensearch/src/main/java/org/opensearch/sql/opensearch/request/PredicateAnalyzer.java:1348-1361:

public QueryExpression like(LiteralExpression literal, boolean caseSensitive) {
  String fieldName = getFieldReference();
  String keywordField = OpenSearchTextType.toKeywordSubField(fieldName, this.rel.getExprType());
  boolean isKeywordField = keywordField != null;
  if (isKeywordField) {
    builder = wildcardQuery(keywordField, ...).caseInsensitive(!caseSensitive);
    return this;
  }
  throw new UnsupportedOperationException("Like query is not supported for text field");
}

The throw is caught at PredicateAnalyzer.java:239-249 (broad catch (Throwable)) and falls back to ScriptQueryExpression, which reads _source per doc.

The comment at :1343-1346 explains why: emitting wildcard_query against analyzed text would change LIKE semantics, since Lucene wildcards run per-token. This was an intentional correctness-over-performance choice — see Related Issues.

Proposal — Issue 2

Both an optimization and a doc update are needed; they reinforce each other.

Optimization — rewrite LIKE(text_field, '%LITERAL%') to match_phrase

Add a planner-level rewrite that fires when all of the following hold:

• Field is text without a .keyword subfield (the keyword path already pushes down via wildcard_query).
• 2-arg LIKE. 3-arg LIKE with explicit case-sensitive flag falls through to the current script path.
• Pattern shape is exactly '%LITERAL%' — leading and trailing % only, no interior %/_, no \-escapes. All other shapes (no wildcards, prefix-only, suffix-only, interior wildcards) fall through to the current script path.
• The field's analyzer applied to LITERAL produces ≥1 token and those tokens survive without stopword/stemming loss. Cache the analyzer check per (field, literal).
• Cluster setting plugins.calcite.like_to_match_phrase.enabled is on. Default off because the rewrite is analyzer-driven (case-insensitive under standard analyzer) and LIKE is contractually case-sensitive per #4835.

Target is match_phrase, not match. Phrase semantics preserve token adjacency — closer to substring intent on analyzed text. Multi-token literals work; single-token degenerates to match correctly.

Other LIKE patterns on text fields ('LITERAL', 'LITERAL%', '%LITERAL', patterns with interior wildcards) cannot be safely rewritten with current Lucene primitives — they require character-anchored or character-position-aware matching that token-based queries can't express. They remain on the script path.

Blocker: #3668 — match_phrase doesn't push down on Calcite yet. The rewrite is moot until that lands, otherwise it just exchanges one script path for another.

Documentation — call out which LIKE patterns get optimized

Add a "performance notes" section to docs/user/ppl/cmd/where.md (or a dedicated page). The user-facing message must be specific about what is and isn't optimized:

LIKE pattern on a text field	engine behavior
'%LITERAL%' (substring)	Optimized to match_phrase when the opt-in setting is enabled — fast.
'LITERAL' (no wildcards, exact match)	Per-doc source scan — slow. Use body_field.keyword = 'LITERAL' or restructure data.
'LITERAL%' (prefix)	Per-doc source scan — slow. Use a .keyword subfield + LIKE on the subfield.
'%LITERAL' (suffix)	Per-doc source scan — slow. No fast alternative on text; use .keyword.
any pattern with interior %/_	Per-doc source scan — slow. No optimization.

Also document:

• Adding a .keyword subfield to the mapping is the most general fix — it routes all LIKE patterns through wildcard_query against the subfield, which is fast.
• match_phrase(text_field, "literal") is always available as a direct alternative — the optimization above is just an automatic version of this rewrite for the substring case.
• Cross-reference #4835 for the case-sensitivity gotcha (any LIKE is implicitly ILIKE today).

Not proposing:

• A change to default LIKE semantics — conflicts with #3428 and #4835.
• A blanket LIKE → match rewrite — match defaults to OR over tokens, would over-match on multi-token literals.
• Optimization for LIKE patterns other than '%LITERAL%' — doc must clearly state these still scan the source.

Reproduction

Index template:

PUT logs-test
{
  "mappings": {
    "properties": {
      "body_text":    {"type": "text"},
      "body_keyword": {"type": "keyword"},
      "body_multi":   {"type": "text", "fields": {"keyword": {"type": "keyword", "ignore_above": 32766}}}
    }
  }
}

Bulk-load 5000 docs where each body_* field holds a string like logtype=<lt> http_status=<n> uri="..." user_agent="..." with <lt> randomly drawn from the four logtypes.

Each cell ran via:

• POST /_plugins/_ppl/_explain to extract DSL pushdown shape
• POST /_plugins/_ppl to capture hit count

Calcite engine enabled (plugins.calcite.enabled: true).

Related issues

• #3669 — Original feature request to push down LIKE on Calcite.
• #3915 (merged 2025-08-13) — Introduced today's behavior. PR description: "we should only support pushdown like query for keyword field".
• #3950 (closed 2025-10-22) — Asked for a _source script fallback to fill the text-field gap. Closed by:
• #4010 (merged 2025-08-19) — Accepted the script path itself. That's exactly what we observe.
• #3428 — Provides the semantic counterexamples (e.g., Amber Johnny vs Ambe_) cited as the reason NOT to emit wildcard_query for LIKE on tokenized text.
• #4835 — LIKE should be case-sensitive in PPL but currently isn't (every LIKE cell in the matrix shows ILIKE / case_insensitive=true). Constrains any rewrite target.
• #3668 — Open, unassigned. match_phrase doesn't push down on Calcite yet. Hard prerequisite for any LIKE → match_phrase rewrite to be useful, and the underlying cause of the rex-derived-column hard-fail in Issue 1.

Acceptance criteria

Issue 1 — early failure / docs:

• Planner detects relevance functions on non-pushdownable columns and fails at planning time with a clear, user-facing error.
• PPL relevance-function docs describe whole-value matching on keyword fields and the derived-column restriction.

Issue 2 — optimization (follow-up issue once #3668 ships):

• Cluster setting plugins.calcite.like_to_match_phrase.enabled added, default off.
• Rewrite emits match_phrase only for '%LITERAL%' on a text field with no .keyword subfield, 2-arg LIKE, and analyzer-token-preserving literal.
• All other LIKE patterns fall through to the current script path unchanged.
• Test coverage: standard analyzer, multi-token literals, hyphenated literals, prefix-only / suffix-only / no-wildcard / interior-wildcard patterns (must fall through), escape character LIKE, case-sensitive 3-arg LIKE (must fall through), missing field, NULL handling.

Issue 2 — documentation:

• Performance-notes page lists each LIKE pattern shape and whether it's optimized or scans source.
• where.md and the relevance-functions page cross-link to it.
• Documentation describes the opt-in setting and the conditions under which the rewrite fires.

Reproduction artifacts

Available on request:

• gen_logs_multi.py — sample data generator.
• matrix.py — runs the full matrix against localhost:9200.
• Saved EXPLAIN responses showing the verbatim DSL for each cell.