fix(opensearch): pass positional args to transport.perform_request for ddtrace compatibility

[Copilot]

• Add inline comment above both transport.perform_request(...) calls in _query_sql and _query_sql_async explaining why positional args are used (ddtrace compatibility)

Original prompt

Issue Title: ddtrace issue when using sqlmetadataretriever
Issue Description: ### Problem

When OpenSearchSQLRetriever executes a SQL query, ddtrace's Elasticsearch patch intercepts _client.transport.perform_request() and attempts to unpack (method, target) = args. The call arrives with 0 positional arguments, raising a ValueError that propagates as DocumentStoreError: Failed to execute SQL query in OpenSearch: not enough values to unpack (expected 2, got 0).

Customer / Business Impact

Customers (flagged via Sols) using OpenSearchSQLRetriever in environments with Datadog APM (ddtrace) active are completely blocked from executing SQL queries against OpenSearch. All such requests return HTTP 400.

Expected Behaviour

SQL queries via OpenSearchSQLRetriever should execute successfully regardless of whether Datadog APM (ddtrace) instrumentation is active in the environment.

How to Reproduce

1. Enable Datadog APM (ddtrace) instrumentation in the Haystack service.
2. Use the OpenSearchSQLRetriever component (or call OpenSearchDocumentStore._query_sql() directly).
3. Run a SQL query, e.g. SELECT COUNT(*) AS file_count FROM file WHERE file_name IS NOT NULL;
4. Observe the 400 error with ValueError: not enough values to unpack (expected 2, got 0) inside the ddtrace Elasticsearch patch.

Code / Configuration

Component configuration used at time of repro:

{
  "component_type": "haystack_integrations.components.retrievers.opensearch.sql_retriever.OpenSearchSQLRetriever",
  "init_params": {
    "raise_on_failure": true,
    "fetch_size": 1000,
    "document_store": {
      "type": "haystack_integrations.document_stores.opensearch.document_store.OpenSearchDocumentStore",
      "init_parameters": {
        "index": "Standard-Index-English",
        "max_chunk_bytes": 104857600,
        "embedding_dim": 768,
        "return_embedding": false,
        "settings": {"index.knn": true},
        "create_index": true
      }
    }
  },
  "input": {
    "query": "SELECT COUNT(*) AS file_count FROM file WHERE file_name IS NOT NULL;"
  }
}

Full stack trace from API response:

Error running component haystack_integrations.components.retrievers.opensearch.sql_retriever.OpenSearchSQLRetriever:
haystack.document_stores.errors.errors.DocumentStoreError: Failed to execute SQL query in OpenSearch: not enough values to unpack (expected 2, got 0)

Traceback (most recent call last):
  File "/home/haystackd/.local/lib/python3.12/site-packages/haystack_integrations/document_stores/opensearch/document_store.py", line 2006, in _query_sql
    response_data = self._client.transport.perform_request(
  File "/home/haystackd/.local/lib/python3.12/site-packages/ddtrace/contrib/internal/elasticsearch/patch.py", line 249, in _perform_request
    result = next(coro)
  File "/home/haystackd/.local/lib/python3.12/site-packages/ddtrace/contrib/internal/elasticsearch/patch.py", line 154, in _perform_request
    method, target = args
ValueError: not enough values to unpack (expected 2, got 0)

The above exception was the direct cause of the following exception:

  File "/home/haystackd/.local/lib/python3.12/site-packages/dc_haystack_utilities/api/haystack/haystack_service.py", line 468, in run_component
    output: Mapping[str, Any] = component.run(**component_input)
  File "/home/haystackd/.local/lib/python3.12/site-packages/haystack_integrations/components/retrievers/opensearch/sql_retriever.py", line 125, in run
    raise e
  File "/home/haystackd/.local/lib/python3.12/site-packages/haystack_integrations/components/retrievers/opensearch/sql_retriever.py", line 122, in run
    result = doc_store._query_sql(query=query, fetch_size=fetch_size)
  File "/home/haystackd/.local/lib/python3.12/site-packages/haystack_integrations/document_stores/opensearch/document_store.py", line 2015, in _query_sql
    raise DocumentStoreError(msg) from e
haystack.document_stores.errors.errors.DocumentStoreError: Failed to execute SQL query in OpenSearch: not enough values to unpack (expected 2, got 0)

Acceptance Criteria

• SQL queries via OpenSearchSQLRetriever succeed without errors when ddtrace is active.
• Users no longer see "Failed to execute SQL query in OpenSearch" errors caused by the Datadog instrumentation's argument-unpacking incompatibility with the OpenSearch client's perform_request signature.

Additional Context

The root cause is in ddtrace/contrib/internal/elasticsearch/patch.py line 154: method, target = args assumes positional args but the OpenSearch client passes them differently. This is a ddtrace version compatibility issue with the OpenSearch Python client.

🎥 Jam: https://jam.dev/c/887748f3-cfd8-45eb-b173-fd4a30e3d94b

---

Consolidated by Marvin
Fixes https://linear.app/deepset/issue/PIP-226/ddtrace-issue-when-using-sqlmetadataretriever
Branch Name should include the identifier "PIP-226"

Issue ...

[github-actions]

Coverage report (opensearch)

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
integrations/opensearch/src/haystack_integrations/document_stores/opensearch
document_store.py
Project Total

This report was generated by python-coverage-comment-action

[anakin87]

I left a few minor comments

[anakin87]

let's add a comment explaining why we use positional args here, so we don't forget in the future

[anakin87]

let's add a comment explaining why we use positional args here, so we don't forget in the future

[anakin87]

Looks good