python/ebook_search/bm25_corpus.py

@@ -5,7 +5,6 @@ from __future__ import annotations
 import json
 import logging
 import shutil
-import tempfile
 from dataclasses import dataclass
 from datetime import UTC, datetime
 from functools import cache
@@ -59,13 +58,21 @@ class BM25CorpusUnavailableError(RuntimeError):
 
 
 def bm25_index_path(config: EbookSearchConfig) -> Path:
-    """Return the configured BM25 index path relative to the current working directory."""
+    """Return the configured BM25 index root path relative to the current working directory."""
     path = Path(config.bm25_index_dir).expanduser()
     if path.is_absolute():
         return path
     return Path.cwd() / path
 
 
+def get_current_bm25_index(index_path: Path) -> Path:
+    """Return the live BM25 index directory."""
+    current_path = index_path / "current"
+    if current_path.exists() or current_path.is_symlink():
+        return current_path
+    return index_path
+
+
 def ensure_bm25_corpus(session: Session, config: EbookSearchConfig) -> None:
     """Create or refresh the persisted BM25 corpus when it is missing or stale."""
     index_path = bm25_index_path(config)
@@ -100,13 +107,13 @@ def refresh_bm25_corpus(
 ) -> BM25Manifest:
     """Rebuild and persist the BM25 corpus from the current database chunks."""
     index_path = bm25_index_path(config)
-    records = fetch_bm25_corpus_records(session)
+    records, texts = fetch_bm25_corpus_records(session)
     manifest = BM25Manifest(
         created_at=datetime.now(tz=UTC),
         db_updated_at=db_updated_at if db_updated_at is not None else corpus_last_updated_at(session),
         chunk_count=len(records),
     )
-    write_bm25_corpus(index_path, records, manifest)
+    write_bm25_corpus(index_path, records, texts, manifest)
     logger.info(
         "ebook_bm25_index_refreshed path=%s chunks=%s created_at=%s",
         index_path,
@@ -123,7 +130,8 @@ def load_bm25_corpus(config: EbookSearchConfig) -> BM25Corpus:
     Background refresh tasks clear this cache after rebuilding the on-disk corpus.
     """
     index_path = bm25_index_path(config)
-    logger.info("ebook_bm25_corpus_cache_load path=%s", index_path)
+    active_index_path = get_current_bm25_index(index_path)
+    logger.info("ebook_bm25_corpus_cache_load path=%s active_path=%s", index_path, active_index_path)
     manifest = read_bm25_manifest(index_path)
     if manifest is None or not bm25_index_exists(index_path, manifest):
         msg = f"BM25 corpus is not available: {index_path}"
@@ -131,7 +139,7 @@ def load_bm25_corpus(config: EbookSearchConfig) -> BM25Corpus:
     if manifest.chunk_count == 0:
         return BM25Corpus(retriever=None, records=(), manifest=manifest)
 
-    retriever = bm25s.BM25.load(index_path, load_corpus=True, mmap=True)
+    retriever = bm25s.BM25.load(active_index_path, load_corpus=True, mmap=True)
     records = tuple(dict(record) for record in retriever.corpus)
     return BM25Corpus(retriever=retriever, records=records, manifest=manifest)
 
@@ -156,8 +164,12 @@ def score_bm25_corpus(query: str, corpus: BM25Corpus, *, limit: int) -> list[tup
     return results
 
 
-def fetch_bm25_corpus_records(session: Session) -> list[dict[str, object]]:
-    """Fetch BM25 corpus records from the database."""
+def fetch_bm25_corpus_records(session: Session) -> tuple[list[dict[str, object]], list[str]]:
+    """Fetch persistable BM25 corpus records and their matching index texts from the database.
+
+    search_text is only needed to build the index, so it is returned separately instead of
+    being persisted into the corpus records, which would double the corpus size.
+    """
     statement = (
         select(
             EbookChunk.id.label("chunk_id"),
@@ -173,7 +185,13 @@ def fetch_bm25_corpus_records(session: Session) -> list[dict[str, object]]:
         .outerjoin(EbookChapter, EbookChapter.id == EbookChunk.chapter_id)
         .order_by(EbookChunk.id)
     )
-    return [dict(row) for row in session.execute(statement).mappings()]
+    records: list[dict[str, object]] = []
+    texts: list[str] = []
+    for row in session.execute(statement).mappings():
+        record = dict(row)
+        texts.append(str(record.pop("bm25_text")))
+        records.append(record)
+    return records, texts
 
 
 def corpus_last_updated_at(session: Session) -> datetime | None:
@@ -186,28 +204,42 @@ def corpus_last_updated_at(session: Session) -> datetime | None:
     return session.scalar(select(func.max(update_times.c.updated)))
 
 
-def write_bm25_corpus(index_path: Path, records: list[dict[str, object]], manifest: BM25Manifest) -> None:
-    """Write a BM25 corpus and manifest atomically."""
-    index_path.parent.mkdir(parents=True, exist_ok=True)
-    temp_path = Path(tempfile.mkdtemp(prefix=f"{index_path.name}.", dir=index_path.parent))
+def write_bm25_corpus(
+    index_path: Path,
+    records: list[dict[str, object]],
+    texts: list[str],
+    manifest: BM25Manifest,
+) -> None:
+    """Write a BM25 corpus generation and publish it through the current symlink."""
+    index_path.mkdir(parents=True, exist_ok=True)
+
+    generations_path = index_path / "generations"
+    generations_path.mkdir(exist_ok=True)
+
+    generation_path = next_bm25_generation_path(generations_path, manifest.created_at)
+    current_path = index_path / "current"
+    next_current_path = index_path / f".current.{generation_path.name}.tmp"
     try:
+        generation_path.mkdir()
+
+        # Empty corpora publish a manifest-only generation so startup succeeds before any chunks exist.
         if records:
             retriever = bm25s.BM25()
-            texts = [str(record["bm25_text"]) for record in records]
             retriever.index(bm25s.tokenize(texts, show_progress=False), show_progress=False)
-            retriever.save(temp_path, corpus=records, show_progress=False)
-        write_bm25_manifest(temp_path, manifest)
-        if index_path.exists():
-            shutil.rmtree(index_path)
-        temp_path.rename(index_path)
+            retriever.save(generation_path, corpus=records, show_progress=False)
+        write_bm25_manifest(generation_path, manifest)
+        next_current_path.unlink(missing_ok=True)
+        next_current_path.symlink_to(generation_path, target_is_directory=True)
+        next_current_path.replace(current_path)
     except Exception:
-        shutil.rmtree(temp_path, ignore_errors=True)
+        next_current_path.unlink(missing_ok=True)
+        shutil.rmtree(generation_path, ignore_errors=True)
         raise
 
 
 def read_bm25_manifest(index_path: Path) -> BM25Manifest | None:
     """Read the BM25 manifest if it exists and is valid."""
-    manifest_path = index_path / MANIFEST_NAME
+    manifest_path = get_current_bm25_index(index_path) / MANIFEST_NAME
     if not manifest_path.exists():
         return None
     body = json.loads(manifest_path.read_text(encoding="utf-8"))
@@ -230,8 +262,20 @@ def write_bm25_manifest(index_path: Path, manifest: BM25Manifest) -> None:
 
 def bm25_index_exists(index_path: Path, manifest: BM25Manifest | None) -> bool:
     """Return whether a usable persisted BM25 index exists."""
-    if manifest is None or not index_path.is_dir():
+    active_index_path = get_current_bm25_index(index_path)
+    if manifest is None or not active_index_path.is_dir():
         return False
     if manifest.chunk_count == 0:
         return True
-    return all((index_path / file_name).exists() for file_name in REQUIRED_INDEX_FILES)
+    return all((active_index_path / file_name).exists() for file_name in REQUIRED_INDEX_FILES)
+
+
+def next_bm25_generation_path(generations_path: Path, created_at: datetime) -> Path:
+    """Return an unused dated BM25 generation path."""
+    base_name = created_at.astimezone(UTC).strftime("%Y%m%dT%H%M%S.%fZ")
+    generation_path = generations_path / base_name
+    suffix = 1
+    while generation_path.exists():
+        generation_path = generations_path / f"{base_name}.{suffix}"
+        suffix += 1
+    return generation_path

tests/test_ebook_search_core.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import logging
 from dataclasses import replace
 from datetime import UTC, datetime
 from os import environ
@@ -21,6 +22,9 @@ from python.ebook_search.bm25_corpus import (
     ensure_bm25_corpus,
     fetch_bm25_corpus_records,
     load_bm25_corpus,
+    read_bm25_manifest,
+    score_bm25_corpus,
+    write_bm25_corpus,
 )
 from python.ebook_search.config import EbookSearchConfig, RerankConfig, load_config, normalize_embedding_model
 from python.ebook_search.embeddings import MODEL_DIMENSIONS, ensure_embedding_models
@@ -123,9 +127,11 @@ def test_bm25_corpus_uses_existing_search_text_without_duplicate_metadata() -> N
         )
         session.commit()
 
-        records = fetch_bm25_corpus_records(session)
+        records, texts = fetch_bm25_corpus_records(session)
 
-    assert records[0]["bm25_text"] == "Book Author Chapter content"
+    assert texts == ["Book Author Chapter content"]
+    assert records[0]["chunk_id"] == 1
+    assert "bm25_text" not in records[0]
 
 
 def test_reciprocal_rank_fusion_marks_hybrid_source() -> None:
@@ -227,15 +233,106 @@ def test_bm25_candidates_scores_whole_corpus(monkeypatch) -> None:
     assert [result.bm25_score for result in results] == [1.5]
 
 
-def test_bm25_candidates_raises_when_corpus_is_unavailable(monkeypatch) -> None:
+def test_bm25_candidates_returns_empty_when_corpus_is_unavailable(monkeypatch, caplog) -> None:
     def fake_load_bm25_corpus(_config):
         raise BM25CorpusUnavailableError
 
     monkeypatch.setattr("python.ebook_search.search.load_bm25_corpus", fake_load_bm25_corpus)
     config = EbookSearchConfig(rerank=RerankConfig(enabled=False))
 
-    with pytest.raises(BM25CorpusUnavailableError):
-        bm25_candidates("high", config)
+    with caplog.at_level(logging.WARNING):
+        results = bm25_candidates("high", config)
+
+    assert results == []
+    assert "ebook_bm25_index_unavailable_skipping" in caplog.text
+
+
+def test_write_bm25_corpus_publishes_dated_generation(tmp_path) -> None:
+    index_path = tmp_path / "bm25"
+    index_path.mkdir()
+    generations_path = index_path / "generations"
+    generations_path.mkdir()
+    old_generation = generations_path / "20260101T000000.000000Z"
+    old_generation.mkdir()
+    (old_generation / "sentinel").write_text("old", encoding="utf-8")
+    (index_path / "current").symlink_to(Path("generations") / old_generation.name, target_is_directory=True)
+    manifest = BM25Manifest(
+        created_at=datetime(2026, 6, 12, 1, 2, 3, 456789, tzinfo=UTC),
+        db_updated_at=None,
+        chunk_count=0,
+    )
+
+    write_bm25_corpus(index_path, [], [], manifest)
+
+    current_path = index_path / "current"
+    assert current_path.is_symlink()
+    assert current_path.readlink() == generations_path / "20260612T010203.456789Z"
+    assert old_generation.is_dir()
+    assert (old_generation / "sentinel").read_text(encoding="utf-8") == "old"
+    assert (generations_path / "20260612T010203.456789Z").is_dir()
+    assert read_bm25_manifest(index_path) == manifest
+
+
+def test_write_bm25_corpus_keeps_current_generation_when_publish_fails(monkeypatch, tmp_path) -> None:
+    index_path = tmp_path / "bm25"
+    index_path.mkdir()
+    generations_path = index_path / "generations"
+    generations_path.mkdir()
+    old_generation = generations_path / "20260101T000000.000000Z"
+    old_generation.mkdir()
+    (old_generation / "sentinel").write_text("old", encoding="utf-8")
+    current_path = index_path / "current"
+    current_path.symlink_to(Path("generations") / old_generation.name, target_is_directory=True)
+    original_replace = Path.replace
+
+    def fail_current_replace(self, target):
+        if self.parent == index_path and self.name.startswith(".current.") and target == current_path:
+            msg = "current publish failed"
+            raise OSError(msg)
+        return original_replace(self, target)
+
+    monkeypatch.setattr(Path, "replace", fail_current_replace)
+    manifest = BM25Manifest(
+        created_at=datetime(2026, 6, 12, 1, 2, 3, 456789, tzinfo=UTC),
+        db_updated_at=None,
+        chunk_count=0,
+    )
+
+    with pytest.raises(OSError, match="current publish failed"):
+        write_bm25_corpus(index_path, [], [], manifest)
+
+    assert current_path.readlink() == Path("generations") / old_generation.name
+    assert (old_generation / "sentinel").read_text(encoding="utf-8") == "old"
+    assert not (generations_path / "20260612T010203.456789Z").exists()
+
+
+def test_load_bm25_corpus_uses_current_generation(tmp_path) -> None:
+    load_bm25_corpus.cache_clear()
+    index_path = tmp_path / "bm25"
+    manifest = BM25Manifest(
+        created_at=datetime(2026, 6, 12, 1, 2, 3, 456789, tzinfo=UTC),
+        db_updated_at=None,
+        chunk_count=1,
+    )
+    record = {
+        "chunk_id": 2,
+        "text": "cached",
+        "source_title": "B",
+        "source_author": None,
+        "chapter_title": None,
+        "page_label": None,
+    }
+    write_bm25_corpus(index_path, [record], ["cached phrase"], manifest)
+    config = EbookSearchConfig(rerank=RerankConfig(enabled=False), bm25_index_dir=str(index_path))
+
+    try:
+        corpus = load_bm25_corpus(config)
+    finally:
+        load_bm25_corpus.cache_clear()
+
+    assert corpus.manifest == manifest
+    assert corpus.records[0]["chunk_id"] == 2
+    assert score_bm25_corpus("cached", corpus, limit=10)
 
 
 def test_load_bm25_corpus_caches_disk_load(monkeypatch, tmp_path) -> None: