Bug Description

When BM25 indexes are dropped, their Tapir registry slots are not freed. This prevents creating new indexes even after dropping old ones. A PostgreSQL restart is required to free the slots.

Environment

• PostgreSQL version: 18
• pg_textsearch version: 0.1.1-dev
• Operating system: Linux (Docker container)

Steps to Reproduce

1. Create enough BM25 indexes to approach the registry limit (64 indexes)
2. Drop several indexes
3. Try to create new indexes

-- Create 5 test indexes
CREATE INDEX idx_test_1_bm25 ON my_table USING bm25 (title) WITH (text_config=english);
CREATE INDEX idx_test_2_bm25 ON my_table USING bm25 (title) WITH (text_config=english);
CREATE INDEX idx_test_3_bm25 ON my_table USING bm25 (title) WITH (text_config=english);
CREATE INDEX idx_test_4_bm25 ON my_table USING bm25 (title) WITH (text_config=english);
CREATE INDEX idx_test_5_bm25 ON my_table USING bm25 (title) WITH (text_config=english);

-- Drop all 5 indexes
DROP INDEX idx_test_1_bm25;
DROP INDEX idx_test_2_bm25;
DROP INDEX idx_test_3_bm25;
DROP INDEX idx_test_4_bm25;
DROP INDEX idx_test_5_bm25;

-- Try to create 5 new indexes
CREATE INDEX idx_test_new_1_bm25 ON my_table USING bm25 (title) WITH (text_config=english);
CREATE INDEX idx_test_new_2_bm25 ON my_table USING bm25 (title) WITH (text_config=english);
CREATE INDEX idx_test_new_3_bm25 ON my_table USING bm25 (title) WITH (text_config=english);

Expected Behavior

After dropping indexes, their registry slots should be freed immediately, allowing new indexes to be created without a PostgreSQL restart.

Actual Behavior

New indexes cannot be created even though indexes were dropped. The registry still reports as full and creation fails with:

ERROR: Tapir registry full, cannot register index <oid>

Only a PostgreSQL restart clears the registry and allows new indexes to be created.

Test results:

• Started with 56 indexes (8 free slots)
• Created 5 test indexes → 61 indexes (3 free slots)
• Dropped 5 test indexes → 56 indexes (should have 8 free slots)
• Tried to create 5 new indexes → Only 2 succeeded, 3 failed with "Tapir registry full"

Additional Context

• Registry limit: 64 indexes
• Use case: Partitioned/hypertable with multiple chunks, requiring indexes on each chunk
• This prevents dynamic index management scenarios:
  • Rolling index maintenance (dropping old indexes and creating new ones)
  • Creating indexes on new partitions/chunks
  • Managing indexes within a retention window
• Current workaround: Schedule PostgreSQL restarts to free registry slots, which is not ideal for production