Hi there,
I'm in the process of moving the database part of a social networking
site to GAE.
Each client sends a request to the server every 5 minutes with
location information. From the location I calculate a list of geoboxes
to store with the client's profile if the location is significantly
different from the last request.
If I get requests more often than every 5 minutes, I send back an
empty response (clients send unique id, so a 5 minute memcache object
will tell me if I receive too many requests) so as not to burden the
server too much.
I already have a server up and running (apache, php, postgres) - and I
am experimenting with forwarding requests to GAE to measure load and
performance.
In general everything looks good, but I am getting the occational
error on the server:
One error I get is the datastore timeout. I am quite certain that I
write a record at max. every 5 minutes. For that record I only have
one composite index, and that index only has one list entry - so I
don't have 'exploding indexes'. Although the list may have 30-40
entries, so 30-40 index entries must be created.
The second error I get - less frequently - is data contention. The
record I update (still at max every 5 mins) is unique to each user, so
I don't understand where the contention comes from.
The last error is actually the one that puzzles me the most. Timeout
while doing datastore fetches. Traceback is similar to:
Traceback (most recent call last):
File "/base/python_lib/versions/1/google/appengine/ext/webapp/
__init__.py", line 501, in __call__
handler.get(*groups)
File "/base/data/home/apps/grindrservr/3.332855696947742792/
main.py", line 870, in get
user = User.get_by_key_name(key_name)
File "/base/python_lib/versions/1/google/appengine/ext/db/
__init__.py", line 849, in get_by_key_name
return get(*keys)
File "/base/python_lib/versions/1/google/appengine/ext/db/
__init__.py", line 1044, in get
entities = datastore.Get(keys)
File "/base/python_lib/versions/1/google/appengine/api/
datastore.py", line 221, in Get
raise _ToDatastoreError(err)
File "/base/python_lib/versions/1/google/appengine/api/
datastore.py", line 1965, in _ToDatastoreError
raise errors[err.application_error](err.error_detail)
Timeout
As far as I can tell the get_by_key_name should be so fast that it's
basically instant, so I don't understand the timeout here.
I should state that out of maybe 300.000 requests only about 30 fail,
so that may actually be quite ok. But I would like to understand the
errors and if possible program my way around them.
Any comments greatly appreciated.
Sincerely,
/morten
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