I think there must be a problem with RPCs from backends. Given my continued
attempts to debug this problem and Vinny's suggestion, I setup another
small test case, this time writing to the datastore. I observe the exact
same behaviour: a large percentage of writes to datastore hang (seemingly)
indefinitely. I was writing 750KBs of data. Test code:
import webapp2
from google.appengine.ext import db
from google.appengine.api.logservice import logservice
import logging
class TestEntity(db.Model):
data = db.TextProperty()
class StartHandler(webapp2.RequestHandler):
def debugMessage(self, msg):
logging.debug(msg)
logservice.flush()
def get(self):
data = "f" * 1024 * 750
entity = TestEntity(data=data)
self.debugMessage("Entity created")
entity.put()
self.debugMessage("Entity saved")
app = webapp2.WSGIApplication([
('/_ah/start', StartHandler),
], debug=True)
I ran this with 10 instances, 3 times. The number of successful writes was
7,3 and 7 for each time I tested. The unsuccessful writes hang after
"Entity created" appears in the log but before "Entity saved" is logged
(and these entities do not appear in the datastore). Additional info:
- The max time I waited for this was ~15 minutes; I observed hanging of ~1
hour when I was writing/debugging "real" code though.
- I have tried with both db and ndb. Same behaviour
- Things look ok running on frontends. 60/60 successful writes (using ndb
in this case, didn't test with the older API).
Unless I'm missing something, this seems to be a real problem with backend
instances.
Thanks for any suggestions,
Ben
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