Implement query_namespaces over grpc (#416)

## Problem

I want to maintain parity across REST / GRPC implementations. This PR
adds a query_namespaces implementation for the GRPC index client.

## Solution

Use a ThreadPoolExecutor to execute queries in parallel, then aggregate
the results QueryResultsAggregator.

## Usage

```python
import random
from pinecone.grpc import PineconeGRPC

pc = PineconeGRPC(api_key="key")
index = pc.Index(host="jen1024-dojoi3u.svc.apw5-4e34-81fa.pinecone.io", pool_threads=25)

query_vec = [random.random() for i in range(1024)]
combined_results = index.query_namespaces(
    vector=query_vec,
    namespaces=["ns1", "ns2", "ns3", "ns4"],
    include_values=False,
    include_metadata=True,
    filter={"genre": {"$eq": "drama"}},
    top_k=50
)

for vec in combined_results.matches:
    print(vec.get('id'), vec.get('score'))
print(combined_results.usage)
```

## Type of Change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] This change requires a documentation update
- [ ] Infrastructure change (CI configs, etc)
- [ ] Non-code change (docs, etc)
- [ ] None of the above: (explain here)

## Test Plan

Describe specific steps for validating this change.

pinecone/grpc/base.py

@@ -10,6 +10,7 @@
 from pinecone import Config
 from .config import GRPCClientConfig
 from .grpc_runner import GrpcRunner
+from concurrent.futures import ThreadPoolExecutor
 
 from pinecone_plugin_interface import load_and_install as install_plugins
 
@@ -29,10 +30,12 @@ def __init__(
         config: Config,
         channel: Optional[Channel] = None,
         grpc_config: Optional[GRPCClientConfig] = None,
+        pool_threads: Optional[int] = None,
         _endpoint_override: Optional[str] = None,
     ):
         self.config = config
         self.grpc_client_config = grpc_config or GRPCClientConfig()
+        self.pool_threads = pool_threads
 
         self._endpoint_override = _endpoint_override
 
@@ -58,6 +61,13 @@ def stub_openapi_client_builder(*args, **kwargs):
         except Exception as e:
             _logger.error(f"Error loading plugins in GRPCIndex: {e}")
 
+    @property
+    def threadpool_executor(self):
+        if self._pool is None:
+            pt = self.pool_threads or 10
+            self._pool = ThreadPoolExecutor(max_workers=pt)
+        return self._pool
+
     @property
     @abstractmethod
     def stub_class(self):

pinecone/grpc/index_grpc.py

@@ -1,9 +1,11 @@
 import logging
-from typing import Optional, Dict, Union, List, Tuple, Any, TypedDict, cast
+from typing import Optional, Dict, Union, List, Tuple, Any, TypedDict, Iterable, cast
 
 from google.protobuf import json_format
 
 from tqdm.autonotebook import tqdm
+from concurrent.futures import as_completed, Future
+
 
 from .utils import (
     dict_to_proto_struct,
@@ -35,6 +37,7 @@
     SparseValues as GRPCSparseValues,
 )
 from pinecone import Vector as NonGRPCVector
+from pinecone.data.query_results_aggregator import QueryNamespacesResults, QueryResultsAggregator
 from pinecone.core.grpc.protos.vector_service_pb2_grpc import VectorServiceStub
 from .base import GRPCIndexBase
 from .future import PineconeGrpcFuture
@@ -402,6 +405,49 @@ def query(
             json_response = json_format.MessageToDict(response)
             return parse_query_response(json_response, _check_type=False)
 
+    def query_namespaces(
+        self,
+        vector: List[float],
+        namespaces: List[str],
+        top_k: Optional[int] = None,
+        filter: Optional[Dict[str, Union[str, float, int, bool, List, dict]]] = None,
+        include_values: Optional[bool] = None,
+        include_metadata: Optional[bool] = None,
+        sparse_vector: Optional[Union[GRPCSparseValues, SparseVectorTypedDict]] = None,
+        **kwargs,
+    ) -> QueryNamespacesResults:
+        if namespaces is None or len(namespaces) == 0:
+            raise ValueError("At least one namespace must be specified")
+        if len(vector) == 0:
+            raise ValueError("Query vector must not be empty")
+
+        overall_topk = top_k if top_k is not None else 10
+        aggregator = QueryResultsAggregator(top_k=overall_topk)
+
+        target_namespaces = set(namespaces)  # dedup namespaces
+        futures = [
+            self.threadpool_executor.submit(
+                self.query,
+                vector=vector,
+                namespace=ns,
+                top_k=overall_topk,
+                filter=filter,
+                include_values=include_values,
+                include_metadata=include_metadata,
+                sparse_vector=sparse_vector,
+                async_req=False,
+                **kwargs,
+            )
+            for ns in target_namespaces
+        ]
+
+        only_futures = cast(Iterable[Future], futures)
+        for response in as_completed(only_futures):
+            aggregator.add_results(response.result())
+
+        final_results = aggregator.get_results()
+        return final_results
+
     def update(
         self,
         id: str,

pinecone/grpc/pinecone.py

@@ -124,11 +124,13 @@ def Index(self, name: str = "", host: str = "", **kwargs):
         # Use host if it is provided, otherwise get host from describe_index
         index_host = host or self.index_host_store.get_host(self.index_api, self.config, name)
 
+        pt = kwargs.pop("pool_threads", None) or self.pool_threads
+
         config = ConfigBuilder.build(
             api_key=self.config.api_key,
             host=index_host,
             source_tag=self.config.source_tag,
             proxy_url=self.config.proxy_url,
             ssl_ca_certs=self.config.ssl_ca_certs,
         )
-        return GRPCIndex(index_name=name, config=config, **kwargs)
+        return GRPCIndex(index_name=name, config=config, pool_threads=pt, **kwargs)

tests/integration/data/test_query_namespaces.py

@@ -1,5 +1,4 @@
 import pytest
-import os
 from ..helpers import random_string, poll_stats_for_namespace
 from pinecone.data.query_results_aggregator import (
     QueryResultsAggregatorInvalidTopKError,
@@ -9,9 +8,6 @@
 from pinecone import Vector
 
 
-@pytest.mark.skipif(
-    os.getenv("USE_GRPC") == "true", reason="query_namespaces currently only available via rest"
-)
 class TestQueryNamespacesRest:
     def test_query_namespaces(self, idx):
         ns_prefix = random_string(5)