Re: [python] [flask] [CQLAlchemy] NoHostAvailable on create

[Jeff Jirsa]

The warn is a hint you’ve got tombstones, maybe not a big deal, but a hint at 
your data model. It’s not causing this

The log at INFO is Cassandra connection to your app getting severed, Cassandra 
is saying the reset is on the other side (app side, maybe firewall or something 
in the middle too).

-- 
Jeff Jirsa


> On Jan 5, 2018, at 5:50 PM, Alan Hamlett  wrote:
> 
> Update: Still getting the NoHostAvailable periodically in client logs.
> 
> Also seeing these INFO and WARN messages in
> /var/log/cassandra/system.log
> INFO  [epollEventLoopGroup-2-5] 2018-01-06 01:39:02,412 Message.java:623 - 
> Unexpected exception during request; channel = [id: 0xae99b597, 
> L:/10.1.2.3:9042 - R:/10.1.2.12:54720]
> io.netty.channel.unix.Errors$NativeIoException: syscall:read(...)() failed: 
> Connection reset by peer
> at io.netty.channel.unix.FileDescriptor.readAddress(...)(Unknown 
> Source) ~[netty-all-4.0.44.Final.jar:4.0.44.Final]
> WARN  [ReadStage-1] 2018-01-06 01:39:24,350 ReadCommand.java:533 - Read 344 
> live rows and 2074 tombstone cells for query SELECT * FROM keyspace.heartbeat 
> WHERE user_id = 66b6796d-eb84-4bb9-b9d2-8dc882f4c6ac AND time >= 1515225599 
> AND time <= 1515139200 ORDER BY (time ASC) LIMIT 5000 (see 
> tombstone_warn_threshold)
> 
>> On Tue, Jan 2, 2018 at 8:13 AM, Alan Hamlett  wrote:
>> Still getting the NoHostAvailable with more hosts, just occurring less 
>> frequently. Created a JIRA issue on the Python cassandra-driver tracker:
>> https://datastax-oss.atlassian.net/browse/PYTHON-891
>> 
>>> On Mon, Jan 1, 2018 at 8:43 PM, Alan Hamlett  wrote:
>>> Adding more nodes to the cluster fixed the error. Looks like a bug in 
>>> python-driver connection pool:
>>> 
>>> 1. The connection pool only has one host
>>> 2. A query times out, causing that connection to be removed from the pool
>>> 3. Another query executes, but there are no hosts in the pool
>>> 
 On Mon, Jan 1, 2018 at 12:21 PM, Jeff Jirsa  wrote:
 Well the python driver you reference is a third party driver, because the 
 project doesn’t ship official drivers. You may have better luck looking 
 for a datastax driver support forum, or wait until after the holiday for 
 more people to be checking email.
 
 
 -- 
 Jeff Jirsa
 
 
> On Jan 1, 2018, at 12:14 PM, Alan Hamlett  wrote:
> 
> Still getting the cassandra.cluster.NoHostAvailable error periodically 
> from uWSGI hosts. Setting up the connection with postfork:
> https://github.com/alanhamlett/flask-cqlalchemy/blob/653ed3298af7dd617a972e9f87437f6e53f741b9/flask_cqlalchemy/__init__.py#L56
> 
> Lazy connection is False, Retry connection is True. Could this be a bug 
> in cassandra-driver's connection pooling?
> 
> P.S. Blocking a web app when connection isn't available (default non-lazy 
> connect) is really bad. With a web app you want requests that don't 
> depend on Cassandra to complete, but cassandra-driver blocks all requests 
> when there's no Cassandra connection even if it's not needed for the 
> current web app's request. This design decision gives me very low 
> confidence in the Python cassandra-driver.
> 
>> On Sun, Dec 31, 2017 at 2:34 PM, Alan Hamlett  
>> wrote:
>> Thanks for the reply, I think it's related. However, after using a fork 
>> of Flask-CQLAlchemy with postfork I'm still getting the NoHostAvailable 
>> error once per 4k requests. One strange thing is the error rate doesn't 
>> increase with the number of requests, since some uWSGI clients with ~20k 
>> requests over the same time period have an error rate of once per 20k 
>> requests. Both uWSGI hosts have the same number of worker processes.
>> 
>> Flask-CQLAlchemy Fork with Patch:
>> 
>> https://github.com/alanhamlett/flask-cqlalchemy/tree/a7e5c7c7cf0c51a19be98791dd4c47b72b97d9be
>> 
>> Error Traceback seen after patch applied:
>> 
>> Failed to create connection pool for new host 10.1.2.3:
>> Traceback (most recent call last):
>>   File "cassandra/cluster.py", line 2452, in 
>> cassandra.cluster.Session.add_or_renew_pool.run_add_or_renew_pool
>>   File "cassandra/pool.py", line 332, in 
>> cassandra.pool.HostConnection.__init__
>>   File "cassandra/cluster.py", line 1195, in 
>> cassandra.cluster.Cluster.connection_factory
>>   File "cassandra/connection.py", line 341, in 
>> cassandra.connection.Connection.factory
>> cassandra.OperationTimedOut: errors=Timed out creating connection (5 
>> seconds), last_host=None
>> Traceback (most recent call last):
>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1982, in 
>> wsgi_app
>> response = self.full_dispatch_request()
>>   File 

Re: [python] [flask] [CQLAlchemy] NoHostAvailable on create

[Alan Hamlett]

Update: Still getting the NoHostAvailable periodically in client logs.

Also seeing these INFO and WARN messages in

/var/log/cassandra/system.log

INFO  [epollEventLoopGroup-2-5] 2018-01-06 01:39:02,412
Message.java:623 - Unexpected exception during request; channel = [id:
0xae99b597, L:/10.1.2.3:9042 - R:/10.1.2.12:54720]
io.netty.channel.unix.Errors$NativeIoException: syscall:read(...)()
failed: Connection reset by peer
at io.netty.channel.unix.FileDescriptor.readAddress(...)(Unknown
Source) ~[netty-all-4.0.44.Final.jar:4.0.44.Final]
WARN  [ReadStage-1] 2018-01-06 01:39:24,350 ReadCommand.java:533 -
Read 344 live rows and 2074 tombstone cells for query SELECT * FROM
keyspace.heartbeat WHERE user_id =
66b6796d-eb84-4bb9-b9d2-8dc882f4c6ac AND time >= 1515225599 AND time
<= 1515139200 ORDER BY (time ASC) LIMIT 5000 (see
tombstone_warn_threshold)


On Tue, Jan 2, 2018 at 8:13 AM, Alan Hamlett  wrote:

> Still getting the NoHostAvailable with more hosts, just occurring less
> frequently. Created a JIRA issue on the Python cassandra-driver tracker:
> https://datastax-oss.atlassian.net/browse/PYTHON-891
>
> On Mon, Jan 1, 2018 at 8:43 PM, Alan Hamlett 
> wrote:
>
>> Adding more nodes to the cluster fixed the error. Looks like a bug in
>> python-driver connection pool:
>>
>> 1. The connection pool only has one host
>> 2. A query times out, causing that connection to be removed from the pool
>> 3. Another query executes, but there are no hosts in the pool
>>
>> On Mon, Jan 1, 2018 at 12:21 PM, Jeff Jirsa  wrote:
>>
>>> Well the python driver you reference is a third party driver, because
>>> the project doesn’t ship official drivers. You may have better luck looking
>>> for a datastax driver support forum, or wait until after the holiday for
>>> more people to be checking email.
>>>
>>>
>>> --
>>> Jeff Jirsa
>>>
>>>
>>> On Jan 1, 2018, at 12:14 PM, Alan Hamlett 
>>> wrote:
>>>
>>> Still getting the cassandra.cluster.NoHostAvailable error periodically
>>> from uWSGI hosts. Setting up the connection with postfork:
>>> https://github.com/alanhamlett/flask-cqlalchemy/blob/653ed32
>>> 98af7dd617a972e9f87437f6e53f741b9/flask_cqlalchemy/__init__.py#L56
>>>
>>> Lazy connection is False, Retry connection is True. Could this be a bug
>>> in cassandra-driver's connection pooling?
>>>
>>> P.S. Blocking a web app when connection isn't available (default
>>> non-lazy connect) is really bad. With a web app you want requests that
>>> don't depend on Cassandra to complete, but cassandra-driver blocks all
>>> requests when there's no Cassandra connection even if it's not needed for
>>> the current web app's request. This design decision gives me very low
>>> confidence in the Python cassandra-driver.
>>>
>>> On Sun, Dec 31, 2017 at 2:34 PM, Alan Hamlett 
>>> wrote:
>>>
 Thanks for the reply, I think it's related. However, after using a fork
 of Flask-CQLAlchemy with postfork I'm still getting the NoHostAvailable
 error once per 4k requests. One strange thing is the error rate doesn't
 increase with the number of requests, since some uWSGI clients with ~20k
 requests over the same time period have an error rate of once per 20k
 requests. Both uWSGI hosts have the same number of worker processes.

 *Flask-CQLAlchemy Fork with Patch:*

 https://github.com/alanhamlett/flask-cqlalchemy/tree/a7e5c7c
 7cf0c51a19be98791dd4c47b72b97d9be

 *Error Traceback seen after patch applied:*

 Failed to create connection pool for new host 10.1.2.3:
 Traceback (most recent call last):
   File "cassandra/cluster.py", line 2452, in
 cassandra.cluster.Session.add_or_renew_pool.run_add_or_renew_pool
   File "cassandra/pool.py", line 332, in cassandra.pool.HostConnection.
 __init__
   File "cassandra/cluster.py", line 1195, in
 cassandra.cluster.Cluster.connection_factory
   File "cassandra/connection.py", line 341, in
 cassandra.connection.Connection.factory
 cassandra.OperationTimedOut: errors=Timed out creating connection (5
 seconds), last_host=None
 Traceback (most recent call last):
   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1982,
 in wsgi_app
 response = self.full_dispatch_request()
   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1614,
 in full_dispatch_request
 rv = self.handle_user_exception(e)
   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1517,
 in handle_user_exception
 reraise(exc_type, exc_value, tb)
   File "./venv/lib/python3.4/site-packages/flask/_compat.py", line 33,
 in reraise
 raise value
   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1612,
 in full_dispatch_request
 rv = self.dispatch_request()
   File "./venv/lib/python3.4/site-packages/flask/app.py", 

Re: [python] [flask] [CQLAlchemy] NoHostAvailable on create

[Alan Hamlett]

Still getting the NoHostAvailable with more hosts, just occurring less
frequently. Created a JIRA issue on the Python cassandra-driver tracker:
https://datastax-oss.atlassian.net/browse/PYTHON-891

On Mon, Jan 1, 2018 at 8:43 PM, Alan Hamlett  wrote:

> Adding more nodes to the cluster fixed the error. Looks like a bug in
> python-driver connection pool:
>
> 1. The connection pool only has one host
> 2. A query times out, causing that connection to be removed from the pool
> 3. Another query executes, but there are no hosts in the pool
>
> On Mon, Jan 1, 2018 at 12:21 PM, Jeff Jirsa  wrote:
>
>> Well the python driver you reference is a third party driver, because the
>> project doesn’t ship official drivers. You may have better luck looking for
>> a datastax driver support forum, or wait until after the holiday for more
>> people to be checking email.
>>
>>
>> --
>> Jeff Jirsa
>>
>>
>> On Jan 1, 2018, at 12:14 PM, Alan Hamlett  wrote:
>>
>> Still getting the cassandra.cluster.NoHostAvailable error periodically
>> from uWSGI hosts. Setting up the connection with postfork:
>> https://github.com/alanhamlett/flask-cqlalchemy/blob/653ed32
>> 98af7dd617a972e9f87437f6e53f741b9/flask_cqlalchemy/__init__.py#L56
>>
>> Lazy connection is False, Retry connection is True. Could this be a bug
>> in cassandra-driver's connection pooling?
>>
>> P.S. Blocking a web app when connection isn't available (default non-lazy
>> connect) is really bad. With a web app you want requests that don't depend
>> on Cassandra to complete, but cassandra-driver blocks all requests when
>> there's no Cassandra connection even if it's not needed for the current web
>> app's request. This design decision gives me very low confidence in the
>> Python cassandra-driver.
>>
>> On Sun, Dec 31, 2017 at 2:34 PM, Alan Hamlett 
>> wrote:
>>
>>> Thanks for the reply, I think it's related. However, after using a fork
>>> of Flask-CQLAlchemy with postfork I'm still getting the NoHostAvailable
>>> error once per 4k requests. One strange thing is the error rate doesn't
>>> increase with the number of requests, since some uWSGI clients with ~20k
>>> requests over the same time period have an error rate of once per 20k
>>> requests. Both uWSGI hosts have the same number of worker processes.
>>>
>>> *Flask-CQLAlchemy Fork with Patch:*
>>>
>>> https://github.com/alanhamlett/flask-cqlalchemy/tree/a7e5c7c
>>> 7cf0c51a19be98791dd4c47b72b97d9be
>>>
>>> *Error Traceback seen after patch applied:*
>>>
>>> Failed to create connection pool for new host 10.1.2.3:
>>> Traceback (most recent call last):
>>>   File "cassandra/cluster.py", line 2452, in
>>> cassandra.cluster.Session.add_or_renew_pool.run_add_or_renew_pool
>>>   File "cassandra/pool.py", line 332, in cassandra.pool.HostConnection.
>>> __init__
>>>   File "cassandra/cluster.py", line 1195, in
>>> cassandra.cluster.Cluster.connection_factory
>>>   File "cassandra/connection.py", line 341, in
>>> cassandra.connection.Connection.factory
>>> cassandra.OperationTimedOut: errors=Timed out creating connection (5
>>> seconds), last_host=None
>>> Traceback (most recent call last):
>>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1982, in
>>> wsgi_app
>>> response = self.full_dispatch_request()
>>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1614, in
>>> full_dispatch_request
>>> rv = self.handle_user_exception(e)
>>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1517, in
>>> handle_user_exception
>>> reraise(exc_type, exc_value, tb)
>>>   File "./venv/lib/python3.4/site-packages/flask/_compat.py", line 33,
>>> in reraise
>>> raise value
>>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1612, in
>>> full_dispatch_request
>>> rv = self.dispatch_request()
>>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1598, in
>>> dispatch_request
>>> return self.view_functions[rule.endpoint](**req.view_args)
>>>   File "./app/api_utils.py", line 876, in get_durations
>>> use_cassandra=use_cassandra,
>>>   File "./venv/lib/python3.4/site-packages/datadog/dogstatsd/context.py",
>>> line 53, in wrapped
>>> return func(*args, **kwargs)
>>>   File "./app/api_utils.py", line 1339, in heartbeats_to_durations
>>> for heartbeat in heartbeats:
>>>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>>> line 512, in __iter__
>>> self._execute_query()
>>>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>>> line 469, in _execute_query
>>> self._result_generator = (i for i in self._execute(self._select_que
>>> ry()))
>>>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>>> line 401, in _execute
>>> result = _execute_statement(self.model, statement,
>>> self._consistency, self._timeout, connection=connection)
>>>   File 

Re: [python] [flask] [CQLAlchemy] NoHostAvailable on create

[Alan Hamlett]

Adding more nodes to the cluster fixed the error. Looks like a bug in
python-driver connection pool:

1. The connection pool only has one host
2. A query times out, causing that connection to be removed from the pool
3. Another query executes, but there are no hosts in the pool

On Mon, Jan 1, 2018 at 12:21 PM, Jeff Jirsa  wrote:

> Well the python driver you reference is a third party driver, because the
> project doesn’t ship official drivers. You may have better luck looking for
> a datastax driver support forum, or wait until after the holiday for more
> people to be checking email.
>
>
> --
> Jeff Jirsa
>
>
> On Jan 1, 2018, at 12:14 PM, Alan Hamlett  wrote:
>
> Still getting the cassandra.cluster.NoHostAvailable error periodically
> from uWSGI hosts. Setting up the connection with postfork:
> https://github.com/alanhamlett/flask-cqlalchemy/blob/
> 653ed3298af7dd617a972e9f87437f6e53f741b9/flask_cqlalchemy/__init__.py#L56
>
> Lazy connection is False, Retry connection is True. Could this be a bug in
> cassandra-driver's connection pooling?
>
> P.S. Blocking a web app when connection isn't available (default non-lazy
> connect) is really bad. With a web app you want requests that don't depend
> on Cassandra to complete, but cassandra-driver blocks all requests when
> there's no Cassandra connection even if it's not needed for the current web
> app's request. This design decision gives me very low confidence in the
> Python cassandra-driver.
>
> On Sun, Dec 31, 2017 at 2:34 PM, Alan Hamlett 
> wrote:
>
>> Thanks for the reply, I think it's related. However, after using a fork
>> of Flask-CQLAlchemy with postfork I'm still getting the NoHostAvailable
>> error once per 4k requests. One strange thing is the error rate doesn't
>> increase with the number of requests, since some uWSGI clients with ~20k
>> requests over the same time period have an error rate of once per 20k
>> requests. Both uWSGI hosts have the same number of worker processes.
>>
>> *Flask-CQLAlchemy Fork with Patch:*
>>
>> https://github.com/alanhamlett/flask-cqlalchemy/tree/a7e5c7c
>> 7cf0c51a19be98791dd4c47b72b97d9be
>>
>> *Error Traceback seen after patch applied:*
>>
>> Failed to create connection pool for new host 10.1.2.3:
>> Traceback (most recent call last):
>>   File "cassandra/cluster.py", line 2452, in
>> cassandra.cluster.Session.add_or_renew_pool.run_add_or_renew_pool
>>   File "cassandra/pool.py", line 332, in cassandra.pool.HostConnection.
>> __init__
>>   File "cassandra/cluster.py", line 1195, in
>> cassandra.cluster.Cluster.connection_factory
>>   File "cassandra/connection.py", line 341, in
>> cassandra.connection.Connection.factory
>> cassandra.OperationTimedOut: errors=Timed out creating connection (5
>> seconds), last_host=None
>> Traceback (most recent call last):
>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1982, in
>> wsgi_app
>> response = self.full_dispatch_request()
>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1614, in
>> full_dispatch_request
>> rv = self.handle_user_exception(e)
>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1517, in
>> handle_user_exception
>> reraise(exc_type, exc_value, tb)
>>   File "./venv/lib/python3.4/site-packages/flask/_compat.py", line 33,
>> in reraise
>> raise value
>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1612, in
>> full_dispatch_request
>> rv = self.dispatch_request()
>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1598, in
>> dispatch_request
>> return self.view_functions[rule.endpoint](**req.view_args)
>>   File "./app/api_utils.py", line 876, in get_durations
>> use_cassandra=use_cassandra,
>>   File "./venv/lib/python3.4/site-packages/datadog/dogstatsd/context.py",
>> line 53, in wrapped
>> return func(*args, **kwargs)
>>   File "./app/api_utils.py", line 1339, in heartbeats_to_durations
>> for heartbeat in heartbeats:
>>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>> line 512, in __iter__
>> self._execute_query()
>>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>> line 469, in _execute_query
>> self._result_generator = (i for i in self._execute(self._select_que
>> ry()))
>>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>> line 401, in _execute
>> result = _execute_statement(self.model, statement, self._consistency,
>> self._timeout, connection=connection)
>>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>> line 1505, in _execute_statement
>> return conn.execute(s, params, timeout=timeout, connection=connection)
>>   File 
>> "./venv/lib/python3.4/site-packages/cassandra/cqlengine/connection.py",
>> line 341, in execute
>> result = conn.session.execute(query, params, timeout=timeout)
>>   File "cassandra/cluster.py", line 2122, in
>> 

Re: [python] [flask] [CQLAlchemy] NoHostAvailable on create

[Jeff Jirsa]

Well the python driver you reference is a third party driver, because the 
project doesn’t ship official drivers. You may have better luck looking for a 
datastax driver support forum, or wait until after the holiday for more people 
to be checking email.


-- 
Jeff Jirsa


> On Jan 1, 2018, at 12:14 PM, Alan Hamlett  wrote:
> 
> Still getting the cassandra.cluster.NoHostAvailable error periodically from 
> uWSGI hosts. Setting up the connection with postfork:
> https://github.com/alanhamlett/flask-cqlalchemy/blob/653ed3298af7dd617a972e9f87437f6e53f741b9/flask_cqlalchemy/__init__.py#L56
> 
> Lazy connection is False, Retry connection is True. Could this be a bug in 
> cassandra-driver's connection pooling?
> 
> P.S. Blocking a web app when connection isn't available (default non-lazy 
> connect) is really bad. With a web app you want requests that don't depend on 
> Cassandra to complete, but cassandra-driver blocks all requests when there's 
> no Cassandra connection even if it's not needed for the current web app's 
> request. This design decision gives me very low confidence in the Python 
> cassandra-driver.
> 
>> On Sun, Dec 31, 2017 at 2:34 PM, Alan Hamlett  wrote:
>> Thanks for the reply, I think it's related. However, after using a fork of 
>> Flask-CQLAlchemy with postfork I'm still getting the NoHostAvailable error 
>> once per 4k requests. One strange thing is the error rate doesn't increase 
>> with the number of requests, since some uWSGI clients with ~20k requests 
>> over the same time period have an error rate of once per 20k requests. Both 
>> uWSGI hosts have the same number of worker processes.
>> 
>> Flask-CQLAlchemy Fork with Patch:
>> 
>> https://github.com/alanhamlett/flask-cqlalchemy/tree/a7e5c7c7cf0c51a19be98791dd4c47b72b97d9be
>> 
>> Error Traceback seen after patch applied:
>> 
>> Failed to create connection pool for new host 10.1.2.3:
>> Traceback (most recent call last):
>>   File "cassandra/cluster.py", line 2452, in 
>> cassandra.cluster.Session.add_or_renew_pool.run_add_or_renew_pool
>>   File "cassandra/pool.py", line 332, in 
>> cassandra.pool.HostConnection.__init__
>>   File "cassandra/cluster.py", line 1195, in 
>> cassandra.cluster.Cluster.connection_factory
>>   File "cassandra/connection.py", line 341, in 
>> cassandra.connection.Connection.factory
>> cassandra.OperationTimedOut: errors=Timed out creating connection (5 
>> seconds), last_host=None
>> Traceback (most recent call last):
>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1982, in 
>> wsgi_app
>> response = self.full_dispatch_request()
>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1614, in 
>> full_dispatch_request
>> rv = self.handle_user_exception(e)
>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1517, in 
>> handle_user_exception
>> reraise(exc_type, exc_value, tb)
>>   File "./venv/lib/python3.4/site-packages/flask/_compat.py", line 33, in 
>> reraise
>> raise value
>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1612, in 
>> full_dispatch_request
>> rv = self.dispatch_request()
>>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1598, in 
>> dispatch_request
>> return self.view_functions[rule.endpoint](**req.view_args)
>>   File "./app/api_utils.py", line 876, in get_durations
>> use_cassandra=use_cassandra,
>>   File "./venv/lib/python3.4/site-packages/datadog/dogstatsd/context.py", 
>> line 53, in wrapped
>> return func(*args, **kwargs)
>>   File "./app/api_utils.py", line 1339, in heartbeats_to_durations
>> for heartbeat in heartbeats:
>>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py", 
>> line 512, in __iter__
>> self._execute_query()
>>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py", 
>> line 469, in _execute_query
>> self._result_generator = (i for i in self._execute(self._select_query()))
>>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py", 
>> line 401, in _execute
>> result = _execute_statement(self.model, statement, self._consistency, 
>> self._timeout, connection=connection)
>>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py", 
>> line 1505, in _execute_statement
>> return conn.execute(s, params, timeout=timeout, connection=connection)
>>   File 
>> "./venv/lib/python3.4/site-packages/cassandra/cqlengine/connection.py", line 
>> 341, in execute
>> result = conn.session.execute(query, params, timeout=timeout)
>>   File "cassandra/cluster.py", line 2122, in 
>> cassandra.cluster.Session.execute
>>   File "cassandra/cluster.py", line 3982, in 
>> cassandra.cluster.ResponseFuture.result
>> cassandra.cluster.NoHostAvailable: ('Unable to complete the operation 
>> against any hosts', {})
>> 
>>> On Sun, Dec 31, 2017 at 9:04 AM, Jeff Jirsa  wrote:
>>> uWSGI forks and the driver / cqlalchemy 

Re: [python] [flask] [CQLAlchemy] NoHostAvailable on create

[Alan Hamlett]

Still getting the cassandra.cluster.NoHostAvailable error periodically from
uWSGI hosts. Setting up the connection with postfork:
https://github.com/alanhamlett/flask-cqlalchemy/blob/653ed3298af7dd617a972e9f87437f6e53f741b9/flask_cqlalchemy/__init__.py#L56

Lazy connection is False, Retry connection is True. Could this be a bug in
cassandra-driver's connection pooling?

P.S. Blocking a web app when connection isn't available (default non-lazy
connect) is really bad. With a web app you want requests that don't depend
on Cassandra to complete, but cassandra-driver blocks all requests when
there's no Cassandra connection even if it's not needed for the current web
app's request. This design decision gives me very low confidence in the
Python cassandra-driver.

On Sun, Dec 31, 2017 at 2:34 PM, Alan Hamlett 
wrote:

> Thanks for the reply, I think it's related. However, after using a fork of
> Flask-CQLAlchemy with postfork I'm still getting the NoHostAvailable error
> once per 4k requests. One strange thing is the error rate doesn't increase
> with the number of requests, since some uWSGI clients with ~20k requests
> over the same time period have an error rate of once per 20k requests. Both
> uWSGI hosts have the same number of worker processes.
>
> *Flask-CQLAlchemy Fork with Patch:*
>
> https://github.com/alanhamlett/flask-cqlalchemy/tree/
> a7e5c7c7cf0c51a19be98791dd4c47b72b97d9be
>
> *Error Traceback seen after patch applied:*
>
> Failed to create connection pool for new host 10.1.2.3:
> Traceback (most recent call last):
>   File "cassandra/cluster.py", line 2452, in cassandra.cluster.Session.add_
> or_renew_pool.run_add_or_renew_pool
>   File "cassandra/pool.py", line 332, in cassandra.pool.HostConnection.
> __init__
>   File "cassandra/cluster.py", line 1195, in cassandra.cluster.Cluster.
> connection_factory
>   File "cassandra/connection.py", line 341, in cassandra.connection.
> Connection.factory
> cassandra.OperationTimedOut: errors=Timed out creating connection (5
> seconds), last_host=None
> Traceback (most recent call last):
>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1982, in
> wsgi_app
> response = self.full_dispatch_request()
>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1614, in
> full_dispatch_request
> rv = self.handle_user_exception(e)
>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1517, in
> handle_user_exception
> reraise(exc_type, exc_value, tb)
>   File "./venv/lib/python3.4/site-packages/flask/_compat.py", line 33, in
> reraise
> raise value
>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1612, in
> full_dispatch_request
> rv = self.dispatch_request()
>   File "./venv/lib/python3.4/site-packages/flask/app.py", line 1598, in
> dispatch_request
> return self.view_functions[rule.endpoint](**req.view_args)
>   File "./app/api_utils.py", line 876, in get_durations
> use_cassandra=use_cassandra,
>   File "./venv/lib/python3.4/site-packages/datadog/dogstatsd/context.py",
> line 53, in wrapped
> return func(*args, **kwargs)
>   File "./app/api_utils.py", line 1339, in heartbeats_to_durations
> for heartbeat in heartbeats:
>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
> line 512, in __iter__
> self._execute_query()
>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
> line 469, in _execute_query
> self._result_generator = (i for i in self._execute(self._select_
> query()))
>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
> line 401, in _execute
> result = _execute_statement(self.model, statement, self._consistency,
> self._timeout, connection=connection)
>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
> line 1505, in _execute_statement
> return conn.execute(s, params, timeout=timeout, connection=connection)
>   File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/connection.py",
> line 341, in execute
> result = conn.session.execute(query, params, timeout=timeout)
>   File "cassandra/cluster.py", line 2122, in cassandra.cluster.Session.
> execute
>   File "cassandra/cluster.py", line 3982, in cassandra.cluster.
> ResponseFuture.result
> cassandra.cluster.NoHostAvailable: ('Unable to complete the operation
> against any hosts', {})
>
> On Sun, Dec 31, 2017 at 9:04 AM, Jeff Jirsa  wrote:
>
>> uWSGI forks and the driver / cqlalchemy may need to reconnect or
>> otherwise fix the state after each fork - you could try to prove this is
>> the cause by checking uWSGI logs or ps for indication that a worker process
>> has exited/been recycled. If you think it may be related to this, check out
>> @postfork decorator
>>
>>
>> --
>> Jeff Jirsa
>>
>>
>> On Dec 31, 2017, at 8:52 AM, Alan Hamlett  wrote:
>>
>> More info: The NoHostAvailable error is happening at random times on each
>> client host, 

Re: [python] [flask] [CQLAlchemy] NoHostAvailable on create

[Alan Hamlett]

Thanks for the reply, I think it's related. However, after using a fork of
Flask-CQLAlchemy with postfork I'm still getting the NoHostAvailable error
once per 4k requests. One strange thing is the error rate doesn't increase
with the number of requests, since some uWSGI clients with ~20k requests
over the same time period have an error rate of once per 20k requests. Both
uWSGI hosts have the same number of worker processes.

*Flask-CQLAlchemy Fork with Patch:*

https://github.com/alanhamlett/flask-cqlalchemy/tree/a7e5c7c7cf0c51a19be98791dd4c47b72b97d9be

*Error Traceback seen after patch applied:*

Failed to create connection pool for new host 10.1.2.3:
Traceback (most recent call last):
  File "cassandra/cluster.py", line 2452, in
cassandra.cluster.Session.add_or_renew_pool.run_add_or_renew_pool
  File "cassandra/pool.py", line 332, in
cassandra.pool.HostConnection.__init__
  File "cassandra/cluster.py", line 1195, in
cassandra.cluster.Cluster.connection_factory
  File "cassandra/connection.py", line 341, in
cassandra.connection.Connection.factory
cassandra.OperationTimedOut: errors=Timed out creating connection (5
seconds), last_host=None
Traceback (most recent call last):
  File "./venv/lib/python3.4/site-packages/flask/app.py", line 1982, in
wsgi_app
response = self.full_dispatch_request()
  File "./venv/lib/python3.4/site-packages/flask/app.py", line 1614, in
full_dispatch_request
rv = self.handle_user_exception(e)
  File "./venv/lib/python3.4/site-packages/flask/app.py", line 1517, in
handle_user_exception
reraise(exc_type, exc_value, tb)
  File "./venv/lib/python3.4/site-packages/flask/_compat.py", line 33, in
reraise
raise value
  File "./venv/lib/python3.4/site-packages/flask/app.py", line 1612, in
full_dispatch_request
rv = self.dispatch_request()
  File "./venv/lib/python3.4/site-packages/flask/app.py", line 1598, in
dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
  File "./app/api_utils.py", line 876, in get_durations
use_cassandra=use_cassandra,
  File "./venv/lib/python3.4/site-packages/datadog/dogstatsd/context.py",
line 53, in wrapped
return func(*args, **kwargs)
  File "./app/api_utils.py", line 1339, in heartbeats_to_durations
for heartbeat in heartbeats:
  File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
line 512, in __iter__
self._execute_query()
  File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
line 469, in _execute_query
self._result_generator = (i for i in
self._execute(self._select_query()))
  File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
line 401, in _execute
result = _execute_statement(self.model, statement, self._consistency,
self._timeout, connection=connection)
  File "./venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
line 1505, in _execute_statement
return conn.execute(s, params, timeout=timeout, connection=connection)
  File
"./venv/lib/python3.4/site-packages/cassandra/cqlengine/connection.py",
line 341, in execute
result = conn.session.execute(query, params, timeout=timeout)
  File "cassandra/cluster.py", line 2122, in
cassandra.cluster.Session.execute
  File "cassandra/cluster.py", line 3982, in
cassandra.cluster.ResponseFuture.result
cassandra.cluster.NoHostAvailable: ('Unable to complete the operation
against any hosts', {})

On Sun, Dec 31, 2017 at 9:04 AM, Jeff Jirsa  wrote:

> uWSGI forks and the driver / cqlalchemy may need to reconnect or otherwise
> fix the state after each fork - you could try to prove this is the cause by
> checking uWSGI logs or ps for indication that a worker process has
> exited/been recycled. If you think it may be related to this, check out
> @postfork decorator
>
>
> --
> Jeff Jirsa
>
>
> On Dec 31, 2017, at 8:52 AM, Alan Hamlett  wrote:
>
> More info: The NoHostAvailable error is happening at random times on each
> client host, so it's probably a client error. If the Cassandra cluster was
> really offline then all client hosts would report the error at the same
> time instead of different random times. The NoHostAvailable error occurs
> about once every 30 minutes, so most request call Model.create() without
> the error.
>
> On Sun, Dec 31, 2017 at 1:07 AM, Alan Hamlett 
> wrote:
>
>> I'm seeing tracebacks in my Python Flask app when creating rows:
>>
>> Traceback (most recent call last):
>>   File "/opt/app/current/app/api.py", line 1174, in consume_heartbeat
>> Heartbeat.create(**form_data)
>>   File 
>> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/models.py",
>>  line 672, in create
>> return cls.objects.create(**kwargs)
>>   File 
>> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>>  line 977, in create
>> .using(connection=self._connection) \
>>   File 
>> 

Re: [python] [flask] [CQLAlchemy] NoHostAvailable on create

[Jeff Jirsa]

uWSGI forks and the driver / cqlalchemy may need to reconnect or otherwise fix 
the state after each fork - you could try to prove this is the cause by 
checking uWSGI logs or ps for indication that a worker process has exited/been 
recycled. If you think it may be related to this, check out @postfork decorator


-- 
Jeff Jirsa


> On Dec 31, 2017, at 8:52 AM, Alan Hamlett  wrote:
> 
> More info: The NoHostAvailable error is happening at random times on each 
> client host, so it's probably a client error. If the Cassandra cluster was 
> really offline then all client hosts would report the error at the same time 
> instead of different random times. The NoHostAvailable error occurs about 
> once every 30 minutes, so most request call Model.create() without the error.
> 
>> On Sun, Dec 31, 2017 at 1:07 AM, Alan Hamlett  wrote:
>> I'm seeing tracebacks in my Python Flask app when creating rows:
>> 
>> Traceback (most recent call last):
>>   File "/opt/app/current/app/api.py", line 1174, in consume_heartbeat
>> Heartbeat.create(**form_data)
>>   File 
>> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/models.py",
>>  line 672, in create
>> return cls.objects.create(**kwargs)
>>   File 
>> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>>  line 977, in create
>> .using(connection=self._connection) \
>>   File 
>> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/models.py",
>>  line 738, in save
>> if_exists=self._if_exists).save()
>>   File 
>> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>>  line 1476, in save
>> self._execute(insert)
>>   File 
>> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>>  line 1351, in _execute
>> results = _execute_statement(self.model, statement, self._consistency, 
>> self._timeout, connection=connection)
>>   File 
>> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>>  line 1505, in _execute_statement
>> return conn.execute(s, params, timeout=timeout, connection=connection)
>>   File 
>> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/connection.py",
>>  line 341, in execute
>> result = conn.session.execute(query, params, timeout=timeout)
>>   File "cassandra/cluster.py", line 2122, in 
>> cassandra.cluster.Session.execute
>>   File "cassandra/cluster.py", line 3982, in 
>> cassandra.cluster.ResponseFuture.result
>> cassandra.cluster.NoHostAvailable: ('Unable to complete the operation 
>> against any hosts', {})
>> 
>> I'm using the cassandra-driver client library 3.12.0 via Flask-CQLAlchemy 
>> 1.2.0 (https://github.com/thegeorgeous/flask-cqlalchemy) with uWSGI 
>> (https://github.com/unbit/uwsgi).
>> 
>> cassandra.cqlengine.connection.setup is being passed lazy_connect=True and 
>> retry_connect=Truecassandra.cqlengine because lazy_connect=False causes 
>> requests to timeout to the Flask app for some reason.
>> 
>> Also seeing these errors in my uWSGI log file:
>> 
>> [control connection] Error connecting to 10.1.2.3: Traceback (most recent 
>> call last): File "cassandra/cluster.py", line 2781, in 
>> cassandra.cluster.ControlConnection._reconnect_internal File 
>> "cassandra/cluster.py", line 2803, in 
>> cassandra.cluster.ControlConnection._try_connect File 
>> "cassandra/cluster.py", line 1195, in 
>> cassandra.cluster.Cluster.connection_factory File "cassandra/connection.py", 
>> line 341, in cassandra.connection.Connection.factory 
>> cassandra.OperationTimedOut: errors=Timed out creating connection (5 
>> seconds), last_host=None
>> 
>> What's causing these connection and timeout errors? Something related to 
>> Flask-CQLAlchemy?
> 
> 

Re: [python] [flask] [CQLAlchemy] NoHostAvailable on create

[Alan Hamlett]

More info: The NoHostAvailable error is happening at random times on each
client host, so it's probably a client error. If the Cassandra cluster was
really offline then all client hosts would report the error at the same
time instead of different random times. The NoHostAvailable error occurs
about once every 30 minutes, so most request call Model.create() without
the error.

On Sun, Dec 31, 2017 at 1:07 AM, Alan Hamlett 
wrote:

> I'm seeing tracebacks in my Python Flask app when creating rows:
>
> Traceback (most recent call last):
>   File "/opt/app/current/app/api.py", line 1174, in consume_heartbeat
> Heartbeat.create(**form_data)
>   File 
> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/models.py",
>  line 672, in create
> return cls.objects.create(**kwargs)
>   File 
> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>  line 977, in create
> .using(connection=self._connection) \
>   File 
> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/models.py",
>  line 738, in save
> if_exists=self._if_exists).save()
>   File 
> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>  line 1476, in save
> self._execute(insert)
>   File 
> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>  line 1351, in _execute
> results = _execute_statement(self.model, statement, self._consistency, 
> self._timeout, connection=connection)
>   File 
> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
>  line 1505, in _execute_statement
> return conn.execute(s, params, timeout=timeout, connection=connection)
>   File 
> "/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/connection.py",
>  line 341, in execute
> result = conn.session.execute(query, params, timeout=timeout)
>   File "cassandra/cluster.py", line 2122, in cassandra.cluster.Session.execute
>   File "cassandra/cluster.py", line 3982, in 
> cassandra.cluster.ResponseFuture.result
> cassandra.cluster.NoHostAvailable: ('Unable to complete the operation against 
> any hosts', {})
>
>
> I'm using the cassandra-driver client library 3.12.0 via Flask-CQLAlchemy
> 1.2.0 (https://github.com/thegeorgeous/flask-cqlalchemy) with uWSGI (
> https://github.com/unbit/uwsgi).
>
> cassandra.cqlengine.connection.setup is being passed lazy_connect=True
> and retry_connect=Truecassandra.cqlengine because lazy_connect=False
> causes requests to timeout to the Flask app for some reason.
>
> Also seeing these errors in my uWSGI log file:
>
> [control connection] Error connecting to 10.1.2.3: Traceback (most recent 
> call last): File "cassandra/cluster.py", line 2781, in 
> cassandra.cluster.ControlConnection._reconnect_internal File 
> "cassandra/cluster.py", line 2803, in 
> cassandra.cluster.ControlConnection._try_connect File "cassandra/cluster.py", 
> line 1195, in cassandra.cluster.Cluster.connection_factory File 
> "cassandra/connection.py", line 341, in 
> cassandra.connection.Connection.factory cassandra.OperationTimedOut: 
> errors=Timed out creating connection (5 seconds), last_host=None
>
>
> What's causing these connection and timeout errors? Something related to
> Flask-CQLAlchemy?
>

[python] [flask] [CQLAlchemy] NoHostAvailable on create

[Alan Hamlett]

I'm seeing tracebacks in my Python Flask app when creating rows:

Traceback (most recent call last):
  File "/opt/app/current/app/api.py", line 1174, in consume_heartbeat
Heartbeat.create(**form_data)
  File 
"/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/models.py",
line 672, in create
return cls.objects.create(**kwargs)
  File 
"/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
line 977, in create
.using(connection=self._connection) \
  File 
"/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/models.py",
line 738, in save
if_exists=self._if_exists).save()
  File 
"/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
line 1476, in save
self._execute(insert)
  File 
"/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
line 1351, in _execute
results = _execute_statement(self.model, statement,
self._consistency, self._timeout, connection=connection)
  File 
"/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/query.py",
line 1505, in _execute_statement
return conn.execute(s, params, timeout=timeout, connection=connection)
  File 
"/opt/app/current/venv/lib/python3.4/site-packages/cassandra/cqlengine/connection.py",
line 341, in execute
result = conn.session.execute(query, params, timeout=timeout)
  File "cassandra/cluster.py", line 2122, in cassandra.cluster.Session.execute
  File "cassandra/cluster.py", line 3982, in
cassandra.cluster.ResponseFuture.result
cassandra.cluster.NoHostAvailable: ('Unable to complete the operation
against any hosts', {})


I'm using the cassandra-driver client library 3.12.0 via Flask-CQLAlchemy
1.2.0 (https://github.com/thegeorgeous/flask-cqlalchemy) with uWSGI (
https://github.com/unbit/uwsgi).

cassandra.cqlengine.connection.setup is being passed lazy_connect=True and
retry_connect=Truecassandra.cqlengine because lazy_connect=False causes
requests to timeout to the Flask app for some reason.

Also seeing these errors in my uWSGI log file:

[control connection] Error connecting to 10.1.2.3: Traceback (most
recent call last): File "cassandra/cluster.py", line 2781, in
cassandra.cluster.ControlConnection._reconnect_internal File
"cassandra/cluster.py", line 2803, in
cassandra.cluster.ControlConnection._try_connect File
"cassandra/cluster.py", line 1195, in
cassandra.cluster.Cluster.connection_factory File
"cassandra/connection.py", line 341, in
cassandra.connection.Connection.factory cassandra.OperationTimedOut:
errors=Timed out creating connection (5 seconds), last_host=None


What's causing these connection and timeout errors? Something related to
Flask-CQLAlchemy?