Fix connection pool warnings by increasing pool size

in backfiller and downloader, the things making lots of outgoing http requests.

We want these larger sizes anyway to improve performance in downloader and backfiller.

backfiller/backfiller/main.py

@@ -16,6 +16,7 @@ import argh
 import gevent.backdoor
 import gevent.pool
 import prometheus_client as prom
+from requests.adapters import HTTPAdapter
 
 import common
 from common import dateutil
@@ -23,8 +24,10 @@ from common import database
 from common.requests import InstrumentedSession
 from common.segments import list_segment_files, unpadded_b64_decode
 
-# Wraps all requests in some metric collection
+# Wraps all requests in some metric collection and connection pooling
 requests = InstrumentedSession()
+adapter = HTTPAdapter(pool_maxsize=100)
+requests.mount('https://', adapter)
 
 segments_backfilled = prom.Counter(
 	'segments_backfilled',

downloader/downloader/main.py

@@ -15,6 +15,7 @@ import gevent.backdoor
 import gevent.event
 import prometheus_client as prom
 import requests
+import requests.adapters
 from monotonic import monotonic
 
 import common
@@ -305,6 +306,8 @@ class StreamWorker(object):
 		# This worker's SegmentGetters will use its session by default for performance,
 		# but will fall back to a new one if something goes wrong.
 		self.session = common.requests.InstrumentedSession()
+		adapter = requests.adapters.HTTPAdapter(pool_maxsize=100)
+		self.session.mount('https://', adapter)
 		# Map cache is a simple cache to avoid re-downloading the same map URI for every segment,
 		# since it's generally the same but may occasionally change.
 		# We expect the map data to be very small so there is no eviction here.