sheetsync: Only check the most recently changed two sheets most times

Only check the other sheets every 4th time (20sec instead of 5sec).

This elminiates a huge source of unnessecary reads, which prevents us from going over
our API limit.

sheetsync/sheetsync/main.py

@@ -8,9 +8,10 @@ import argh
 import gevent.backdoor
 import gevent.event
 import prometheus_client as prom
-from requests import HTTPError
+from monotonic import monotonic
 from psycopg2 import sql
 from psycopg2.extras import register_uuid
+from requests import HTTPError
 
 import common
 import common.dateutil
@@ -44,15 +45,30 @@ class SheetSync(object):
 
 	# Time between syncs
 	RETRY_INTERVAL = 5
+
 	# Time to wait after getting an error
 	ERROR_RETRY_INTERVAL = 10
 
+	# How many syncs of active sheets to do before checking inactive sheets.
+	# By checking inactive sheets less often, we stay within our API limits.
+	# For example, 4 syncs per inactive check * 5 seconds between syncs = 20s between inactive checks
+	SYNCS_PER_INACTIVE_CHECK = 4
+
+	# How many worksheets to keep "active" based on most recent modify time
+	ACTIVE_SHEET_COUNT = 2
+
+	# Expected quota usage per 100s =
+	#  (100 / RETRY_INTERVAL) * ACTIVE_SHEET_COUNT
+	#  + (100 / RETRY_INTERVAL / SYNCS_PER_INACTIVE_CHECK) * (len(worksheets) - ACTIVE_SHEET_COUNT)
+	# For current values, this is 100/5 * 2 + 100/5/4 * 6 = 70
+
 	def __init__(self, stop, dbmanager, sheets, sheet_id, worksheets, edit_url, bustime_start, allocate_ids=False):
 		self.stop = stop
 		self.dbmanager = dbmanager
 		self.sheets = sheets
 		self.sheet_id = sheet_id
-		self.worksheets = worksheets
+		# map {worksheet: last modify time}
+		self.worksheets = {w: 0 for w in worksheets}
 		self.edit_url = edit_url
 		self.bustime_start = bustime_start
 		self.allocate_ids = allocate_ids
@@ -116,6 +132,9 @@ class SheetSync(object):
 	def run(self):
 		self.conn = self.dbmanager.get_conn()
 
+		# tracks when to do inactive checks
+		sync_count = 0
+
 		while not self.stop.is_set():
 			
 			try:
@@ -123,7 +142,16 @@ class SheetSync(object):
 				# each row is more expensive than the cost of just grabbing the entire table
 				# and comparing locally.
 				events = self.get_events()
-				for worksheet in self.worksheets:
+				if sync_count % self.SYNCS_PER_INACTIVE_CHECK == 0:
+					# check all worksheets
+					worksheets = self.worksheets
+				else:
+					# only check most recently changed worksheets
+					worksheets = sorted(
+						self.worksheets.keys(), key=lambda k: self.worksheets[k], reverse=True,
+					)[:self.ACTIVE_SHEET_COUNT]
+				sync_count += 1
+				for worksheet in worksheets:
 					rows = self.sheets.get_rows(self.sheet_id, worksheet)
 					for row_index, row in enumerate(rows):
 						# Skip first row (ie. the column titles).
@@ -216,6 +244,7 @@ class SheetSync(object):
 			query(self.conn, built_query, sheet_name=worksheet, **row)
 			rows_found.labels(worksheet).inc()
 			rows_changed.labels('insert', worksheet).inc()
+			self.mark_modified(worksheet)
 			return
 
 		rows_found.labels(worksheet).inc()
@@ -237,6 +266,7 @@ class SheetSync(object):
 			))
 			query(self.conn, built_query, **row)
 			rows_changed.labels('input', worksheet).inc()
+			self.mark_modified(worksheet)
 
 		# Update sheet with any changed outputs
 		format_output = lambda v: '' if v is None else v # cast nulls to empty string
@@ -252,6 +282,7 @@ class SheetSync(object):
 					format_output(getattr(event, col)),
 				)
 			rows_changed.labels('output', worksheet).inc()
+			self.mark_modified(worksheet)
 
 		# Set edit link if marked for editing and start/end set.
 		# This prevents accidents / clicking the wrong row and provides
@@ -265,6 +296,12 @@ class SheetSync(object):
 				row_index, self.column_map['edit_link'],
 				edit_link,
 			)
+			self.mark_modified(worksheet)
+
+	def mark_modified(self, worksheet):
+		"""Mark worksheet as having had a change made, bumping it to the top of
+		the most-recently-modified queue."""
+		self.worksheets[worksheet] = monotonic()
 
 
 @argh.arg('dbconnect', help=