Termial output: "access method 'HNSW' does not exist" Error

When running the VectorDB benchmark (VectorDBBench) against PgVector on webui, the test case fails with the error:
access method "HNSW" does not exist
This occurs during the performance test for the 1M dataset with 768-dimensional vectors, specifically when the benchmark attempts to optimize (create) an HNSW index. The error results in the termination of the benchmark run.

1. VDBB Version:1.0.20
   (.venv) [root@server VectorDBBench-1.0.20]#
2. PostgreSQL Version
   `
   [postgres@server ~]$ psql
   psql (18.3)
   Type "help" for help.

postgres=# show server_version;
server_version

18.3
postgres=# show search_path ;
search_path

"$user", public
(1 row)
postgres=# SELECT n.nspname as schema_name, p.proname as function_name
FROM pg_proc p
JOIN pg_namespace n ON p.pronamespace = n.oid
WHERE p.proname = 'hnswhandler';
schema_name | function_name
-------------+---------------
public | hnswhandler
(1 row)

postgres=# SELECT amname FROM pg_am;
amname

heap
btree
hash
gist
gin
spgist
brin
ivfflat
hnsw
(9 rows)
`
3. Configuration information

4.Terminal display details:

Start by reproducing the VectorDBBench web UI performance test against PgVector with the 1M, 768-dimensional dataset, then trace the benchmark path that creates the HNSW index. Check why the PostgreSQL environment reports the HNSW access method as unavailable during creation; done means the benchmark completes without terminating on this error.