add query pool

src/nominatim_db/db/query_pool.py

@@ -0,0 +1,72 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# This file is part of Nominatim. (https://nominatim.org)
+#
+# Copyright (C) 2024 by the Nominatim developer community.
+# For a full list of authors see the git log.
+"""
+A connection pool that executes incoming queries in parallel.
+"""
+from typing import Any, Tuple, Optional
+import asyncio
+import logging
+import time
+
+import psycopg
+
+LOG = logging.getLogger()
+
+QueueItem = Optional[Tuple[psycopg.abc.Query, Any]]
+
+class QueryPool:
+
+    def __init__(self, dsn: str, pool_size: int = 1, **conn_args: Any) -> None:
+        self.wait_time = 0.0
+        self.query_queue: 'asyncio.Queue[QueueItem]' = asyncio.Queue()
+
+        self.pool = [asyncio.create_task(self._worker_loop(dsn, **conn_args))
+                     for _ in range(pool_size)]
+
+
+    async def put_query(self, query: psycopg.abc.Query, params: Any) -> None:
+        tstart = time.time()
+        await self.query_queue.put((query, params))
+        self.wait_time += time.time() - tstart
+
+
+    async def finish(self) -> None:
+        for _ in self.pool:
+            await self.query_queue.put(None)
+
+        tstart = time.time()
+        await asyncio.wait(self.pool)
+        self.wait_time += time.time() - tstart
+
+
+    async def _worker_loop(self, dsn: str, **conn_args: Any) -> None:
+        aconn = await psycopg.AsyncConnection.connect(dsn, **conn_args)
+        async with aconn:
+            async with aconn.cursor() as cur:
+                item = await self.query_queue.get()
+                while item is not None:
+                    try:
+                        if item[1] is None:
+                            await cur.execute(item[0])
+                        else:
+                            await cur.execute(item[0], item[1])
+
+                        item = await self.query_queue.get()
+                    except psycopg.errors.DeadlockDetected:
+                        assert item is not None
+                        LOG.info("Deadlock detected (sql = %s, params = %s), retry.",
+                                 str(item[0]), str(item[1]))
+                        # item is still valid here, causing a retry
+
+
+    async def __aenter__(self) -> 'QueryPool':
+        return self
+
+
+    async def __aexit__(self, exc_type: Any, exc_value: Any, traceback: Any) -> None:
+        await self.finish()
+