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DataStax Cassandra cassandra.cluster.NoHostAvailable

I am consistently getting this error under normal conditions. I am using the Python Cassandra driver (v3.11) to connect locally with RPC enabled. The issue presents itself after a period of time. y assumption was that it was related to max number of connections or queries. Any pointers on where to begin troubleshooting would be greatly appreciated.

Please check if your nodes are really listening by opening up a separate connection from say cqlsh terminal, as you say it is running locally so probably a single node. If that connects, you might want to see how many file handles are open, maybe it is running out of those. We had a similar problem couple of years back, that was attributed to available file handles.

insufficient data in "D" message

I'm using SQLAlchemy scoped sessions to work with a postgresql 9.4 database.
Sometimes I get an error that says "DatabaseError: (DatabaseError) insufficient data in "D" message". I cannot reproduce this error and it happens in an unpredictable way.
After looking at he postgres log files, this error occurs shortly after postgresql logs "could not receive data from client: Connection reset by peer". I guess that means that the connection was cut from the application side. But I don't see anything that could cause this.

It's time to break out your network tools. You have errors on both end that suggests something caused your connection to drop.
It might be hardware, drivers, some bug in your software stack or a proxy / firewall deciding it didn't like the look of your connection and killed it. It's unlikely to be PostgreSQL itself or any of your Python code.
Fire up tcpdump or wireshark and take a look at the packets going back and fore. Ideally on both ends of the connection. That should give you a good indication of where the problem is.

Recover from dropped connection in redis pub/sub

I am running client that is connecting to a redis db. The client is on a WiFi connection and will drop the connection at times. Unfortunately, when this happens, the program just keeps running without throwing any type of warning.
r = redis.StrictRedis(host=XX, password=YY...)
ps = r.pubsub()
ps.subscribe("12345")
for items in ps.listen():
if items['type'] == 'message':
data = items['data']
Ideally, what I am looking for is a catch an event when the connection is lost, try and reestablish the connection, do some error correcting, then get things back up and running. Should this be done in the python program? Should I have an external watchdog?

Unfortunately, one have to 'ping' Redis to check if it is available. If You try to put a value to Redis storage, it will raise an ConnectionError exception if connection is lost. But the listen() generator will not close automatically when connection is lost.
I think that hacking Redis' connection pool could help, give it a try.
P.S. In is very insecure to connect to redis in an untrusted network environment.

This is an old, old question but I linked one of my own questions to it and happened to run across it again. It turned out there was a bug in the redis library that caused the client to enter an infinite loop attempting to reconnect if it lost connection to the redis server. I debugged the issue and PR'd the change. it was merged a long time ago now. Once surfaced the maintainer also knew of a second location that had the same issue.
This problem shouldn't occur anymore.
To fully answer the question, I can't remember which error it is given the time since I fixed this but there is now a specific error returned you can catch and reconnect on.

Getting OperationalError: FATAL: sorry, too many clients already using psycopg2

I am getting the error OperationalError: FATAL: sorry, too many clients already when using psycopg2. I am calling the close method on my connection instance after I am done with it. I am not sure what could be causing this, it is my first experience with python and postgresql, but I have a few years experience with php, asp.net, mysql, and sql server.
EDIT: I am running this locally, if the connections are closing like they should be then I only have 1 connection open at a time. I did have a GUI open to the database but even closed I am getting this error. It is happening very shortly after I run my program. I have a function I call that returns a connection that is opened like:
psycopg2.connect(connectionString)
Thanks
Final Edit:
It was my mistake, I was recursively calling the same method on mistake that was opening the same method over and over. It has been a long day..

This error means what it says, there are too many clients connected to postgreSQL.
Questions you should ask yourself:
Are you the only one connected to this database?
Are you running a graphical IDE?
What method are you using to connect?
Are you testing queries at the same time that you running the code?
Any of these things could be the problem. If you are the admin, you can up the number of clients, but if a program is hanging it open, then that won't help for long.
There are many reasons why you could be having too many clients running at the same time.

Make sure your db connection command isn't in any kind of loop. I was getting the same error from my script until I moved my db.database() out of my programs repeating execution loop.

It simple means many clients are making transaction to PostgreSQL at same time.
I was running Postgis container and Django in different docker container. Hence for my case restarting both db and system container solved the problem.

Pylons error - 'MySQL server has gone away'

I'm using Pylons (a python framework) to serve a simple web application, but it seems to die from time to time, with this in the error log: (2006, 'MySQL server has gone away')
I did a bit of checking, and saw that this was because the connections to MySQL were not being renewed. This shouldn't be a problem though, because the sqlalchemy.pool_recycle in the config file should automatically keep it alive. The default was 3600, but I dialed it back to 1800 because of this problem. It helped a bit, but 3600 should be fine according to the docs. The errors still happen semi-regularly. I don't want to lower it too much though and DOS my own database :).
Maybe something in my MySQL config is goofy? Not sure where to look exactly.
Other relevant details:
Python 2.5
Pylons: 0.9.6.2 (w/ sql_alchemy)
MySQL: 5.0.51

I think I fixed it. It's turns out I had a simple config error. My ini file read:
sqlalchemy.default.url = [connection string here]
sqlalchemy.pool_recycle = 1800
The problem is that my environment.py file declared that the engine would only map keys with the prefix: sqlalchemy.default so pool_recycle was ignored.
The solution is to simply change the second line in the ini to:
sqlalchemy.default.pool_recycle = 1800

You might want to check MySQL's timeout variables:
show variables like '%timeout%';
You're probably interested in wait_timeout (less likely but possible: interactive_timeout). On Debian and Ubuntu, the defaults are 28800 (MySQL kills connections after 8 hours), but maybe the default for your platform is different or whoever administrates the server has configured things differently.
AFAICT, pool_recycle doesn't actually keep the connections alive, it expires them on its own before MySQL kills them. I'm not familiar with pylons, but if causing the connections to intermittently do a SELECT 1; is an option, that will keep them alive at the cost of basically no server load and minimal network traffic. One final thought: are you somehow managing to use a connection that pylons thinks it has expired?