Merge pull request #337 from openbikesensor/next-semaphore

Semaphore for tile requests

api/config.dev.py

@@ -29,5 +29,7 @@ ADDITIONAL_CORS_ORIGINS = [
     "http://localhost:8880/",  # for maputnik on 8880
     "http://localhost:8888/",  # for maputnik on 8888
 ]
+TILE_SEMAPHORE_SIZE = 4
+EXPORT_SEMAPHORE_SIZE = 4
 
 # vim: set ft=python :

api/config.py.example

@@ -61,4 +61,13 @@ TILES_FILE = None
 # default. Python list, or whitespace separated string.
 ADDITIONAL_CORS_ORIGINS = None
 
+# How many asynchronous requests may be sent to the database to generate tile
+# information. Should be less than POSTGRES_POOL_SIZE to leave some connections
+# to the other features of the API ;)
+TILE_SEMAPHORE_SIZE = 4
+
+# How many asynchronous requests may generate exported data simultaneously.
+# Keep this small.
+EXPORT_SEMAPHORE_SIZE = 1
+
 # vim: set ft=python :

api/obs/api/app.py

@@ -1,3 +1,4 @@
+import asyncio
 import logging
 import re
 
@@ -23,7 +24,6 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from obs.api.db import User, make_session, connect_db
 from obs.api.cors import setup_options, add_cors_headers
 from obs.api.utils import get_single_arg
-from sqlalchemy.util import asyncio
 
 log = logging.getLogger(__name__)
 
@@ -58,6 +58,25 @@ app = Sanic(
 )
 configure_sanic_logging()
 
+app.config.update(
+    dict(
+        DEBUG=False,
+        VERBOSE=False,
+        AUTO_RELOAD=False,
+        POSTGRES_POOL_SIZE=20,
+        POSTGRES_MAX_OVERFLOW=40,
+        DEDICATED_WORKER=True,
+        FRONTEND_URL=None,
+        FRONTEND_HTTPS=True,
+        TILES_FILE=None,
+        TILE_SEMAPHORE_SIZE=4,
+        EXPORT_SEMAPHORE_SIZE=1,
+    )
+)
+
+# overwrite from defaults again
+app.config.load_environment_vars("OBS_")
+
 if isfile("./config.py"):
     app.update_config("./config.py")
 
@@ -168,6 +187,12 @@ async def app_connect_db(app, loop):
     )
     app.ctx._db_engine = await app.ctx._db_engine_ctx.__aenter__()
 
+    if app.config.TILE_SEMAPHORE_SIZE:
+        app.ctx.tile_semaphore = asyncio.Semaphore(app.config.TILE_SEMAPHORE_SIZE)
+
+    if app.config.EXPORT_SEMAPHORE_SIZE:
+        app.ctx.export_semaphore = asyncio.Semaphore(app.config.EXPORT_SEMAPHORE_SIZE)
+
 
 @app.after_server_stop
 async def app_disconnect_db(app, loop):

api/obs/api/routes/exports.py

@@ -12,6 +12,7 @@ from sanic.response import raw
 from sanic.exceptions import InvalidUsage
 
 from obs.api.app import api, json as json_response
+from obs.api.utils import use_request_semaphore
 
 
 class ExportFormat(str, Enum):
@@ -26,7 +27,7 @@ def parse_bounding_box(input_string):
             func.ST_Point(left, bottom),
             func.ST_Point(right, top),
         ),
-        3857,
+        4326,
     )
 
 
@@ -60,13 +61,16 @@ def shapefile_zip():
 
 @api.get(r"/export/events")
 async def export_events(req):
+    async with use_request_semaphore(req, "export_semaphore", timeout=30):
         bbox = req.ctx.get_single_arg(
             "bbox", default="-180,-90,180,90", convert=parse_bounding_box
         )
         fmt = req.ctx.get_single_arg("fmt", convert=ExportFormat)
 
         events = await req.ctx.db.stream_scalars(
-        select(OvertakingEvent).where(OvertakingEvent.geometry.bool_op("&&")(bbox))
+            select(OvertakingEvent).where(
+                OvertakingEvent.geometry.bool_op("&&")(func.ST_Transform(bbox, 3857))
+            )
         )
 
         if fmt == ExportFormat.SHAPEFILE:

api/obs/api/routes/tiles.py

@@ -7,10 +7,10 @@ import dateutil.parser
 from sanic.exceptions import Forbidden, InvalidUsage
 from sanic.response import raw
 
-from sqlalchemy import select, text
-from sqlalchemy.sql.expression import table, column
+from sqlalchemy import text
 
 from obs.api.app import app
+from obs.api.utils import use_request_semaphore
 
 
 def get_tile(filename, zoom, x, y):
@@ -87,6 +87,7 @@ def get_filter_options(
 
 @app.route(r"/tiles/<zoom:int>/<x:int>/<y:(\d+)\.pbf>")
 async def tiles(req, zoom: int, x: int, y: str):
+    async with use_request_semaphore(req, "tile_semaphore"):
         if app.config.get("TILES_FILE"):
             tile = get_tile(req.app.config.TILES_FILE, int(zoom), int(x), int(y))
 

api/obs/api/utils.py

@@ -1,12 +1,13 @@
+import asyncio
+from contextlib import asynccontextmanager
 from datetime import datetime
 import logging
+from os.path import commonpath, join, relpath
 import queue
 import tarfile
-from os.path import commonpath, relpath, join
 
 import dateutil.parser
-
-from sanic.exceptions import InvalidUsage
+from sanic.exceptions import InvalidUsage, ServiceUnavailable
 
 log = logging.getLogger(__name__)
 
@@ -127,3 +128,35 @@ class StreamerHelper:
                 await self.response.send(tosend)
             except queue.Empty:
                 break
+
+
+@asynccontextmanager
+async def use_request_semaphore(req, semaphore_name, timeout=10):
+    """
+    If configured, acquire a semaphore for the map tile request and release it
+    after the context has finished.
+
+    If the semaphore cannot be acquired within the timeout, issue a 503 Service
+    Unavailable error response that describes that the database is overloaded,
+    so users know what the problem is.
+
+    Operates as a noop when the tile semaphore is not enabled.
+    """
+    semaphore = getattr(req.app.ctx, semaphore_name, None)
+
+    if semaphore is None:
+        yield
+        return
+
+    try:
+        await asyncio.wait_for(semaphore.acquire(), timeout)
+
+        try:
+            yield
+        finally:
+            semaphore.release()
+
+    except asyncio.TimeoutError:
+        raise ServiceUnavailable(
+            "Too many requests, database overloaded. Please retry later."
+        )