I'm connecting Redshift through Python from PC, Python from Lambda and SQL Workbench.
SQL Workbech always connects without any issues.
Both PC and Lambda often work correctly, but sometimes they can't connect - it looks like connection is waiting for Redshift to accept request, just nothing happens until, for ex. Lambda times out.
There's no log in run, no feedback information, nothing in redshift logs I can find about it.
I can fix every single run manually by connecting in Workbench, while the script is waiting for connection - it apparently refreshes something, allowing Python to connect and work properly.
What is the reason for this and how can I fix it?
Here's my connection:
conn = psycopg2.connect(
host=host,
database=db,
user=user,
password=pwd,
port=port
)
I went through several questions regarding connections like:
AWS Lambda times out connecting to RedShift
AWS Serverless lambda times out while connecting to redshift
python socket Windows 10 connection times out
but nothing looks like its related to my issue.
Found an answer - SQL Workbench blocked the connection. When Workbench is connected, all other sources happen to fail.
Easiest solution is to disconnect Workbench connection before other client tries to connect. If other client already tried connecting, then disconnecting is not enough - it requires reconnecting, so the other client refreshes (I have no idea why, found it by trial and error).
Disconnection may also not work, if there was any error query run in the past and it was not rolled back. After error, rollback and disconnection everything is fine.
Related
I'm trying to execute some long-running SQL queries using SQLAlchemy against a Postgres database hosted on AWS RDS.
from sqlalchemy import create_engine
conn_str = 'postgresql://user:password#db-primary.cluster-cxf.us-west-2.rds.amazonaws.com:5432/dev'
engine = create_engine(conn_str)
sql = 'UPDATE "Clients" SET "Name" = NULL'
#this takes about 4 hrs to execute if run in pgAdmin
with engine.begin() as conn:
conn.execute(sql)
After running for exactly 2 hours, the script errors out with
OperationalError: server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
(Background on this error at: https://sqlalche.me/e/14/e3q8)
I have tested setting connection timeouts in SQLAlchemy (based on How to set connection timeout in SQLAlchemy). This did not make a difference.
I have looked up the connection settings in the Postgres settings (based on https://dba.stackexchange.com/questions/164419/is-it-possible-to-limit-timeout-on-postgres-server), but both statement_timeout and idle_in_transaction_session_timeout are set to 0, meaning there are no set limits.
I agree with #jjanes. This smells like a TCP connection timeout issue. Might be that somewhere in the network layer something, be it a NAT or a firewall, dropped your TCP connection, leaving the code to wait for the full TCP keepalive timeout until it sees the connection as closed. This could happen usually when the network topology between the client and the database is complicated. For example there may be a company firewall, or some sort of interconnection. pgAdmin may come with a pre-configured setting for TCP keepalive, therefore it was not impacted, but I'm not sure.
Other timeouts didn't kick in because, in my understanding, TCP timeout is in the L4 layer, which overshadows other timeouts that are in L7 application layer.
You could try adding the keepalive parameters into your connection string and see if it can resolve the issue. For example:
postgresql://user:password#db-primary.cluster-cxf.us-west-2.rds.amazonaws.com:5432/dev?keepalives_idle=1&keepalives_count=1&tcp_user_timeout=1000
Note the keepalive parameters at the end. For your reference, here's the explanation to those parameters:
https://www.postgresql.org/docs/current/runtime-config-connection.html
I have a mysql server running on my local network that isn't reachable off the network, and it needs to stay like this.
When I am on a different network the following code hangs for about 5-10 seconds, my guess is that its retrying to connect for a number of attempts:
import mysql.connector
conn = mysql.connector.connect(
host="Address",
user="user",
password="password",
database="database"
)
Is there a way to "ping" the mysql server before this code to verify that the MySQL server is reachable or limit the number of retries?
At the moment I am having to use a try-except clause to catch if the server is not reaachable.
Instead of trying to implement specific behavior before connecting, adjust the connect timeout so that you don't have to wait - according to your need, the server is down if you can't connect within a short timeframe anyway.
You can use connection_timeout to adjust the socket timeout used when connecting to the server.
If you set it to a low value (seems like it's in seconds - so 1 should work fine) you'll get the behavior you're looking for (and it will also help you catch any issues with the user/password/database values).
I am writing an app with wxPython that incorporates pyodbc to access SQL Server. A user must first establish a VPN connection before they can establish a connection with the SQL server. In cases where a user forgets to establish a VPN connection or is simply not authorized to access a particular server, the app will freeze for up to 60+ seconds before it produces an error message. Often, users will get impatient and force-close the app before the error message pops up.
I wonder if there is a way to test whether it's possible to connect to the server without freezing up. I thought about using timeout, but it seems that timeout can be used only after I establish a connection
A sample connection string I use is below:
connection = pyodbc.connect(r'DRIVER={SQL Server};SERVER=ServerName;database=DatabaseName;Trusted_Connection=True;unicode_results=True')
See https://code.google.com/archive/p/pyodbc/wikis/Connection.wiki under timeout
Note: This attribute only affects queries. To set the timeout for the
actual connection process, use the timeout keyword of the
pyodbc.connect function.
So change your connection string to:
connection = pyodbc.connect(r'DRIVER={SQL Server};SERVER=ServerName;database=DatabaseName;Trusted_Connection=True;unicode_results=True', timeout=3)
should work
took a while before it threw an error message about server not existing or access being denied
Your comment conflates two very different kinds of errors:
server not existing is a network error. Either the name has no address, or the address is unreachable. No connection can be made.
access being denied is a response from the server. For the server to respond, a connection must exist. This is not to be confused with connection refused (ECONNREFUSED), which means the remote is not accepting connections on the port.
SQL Server uses TCP/IP. You can use standard network functions to determine if the network hostname of the machine running SQL Server can be found, and if the IP address is reachable. One advantage to using them to "pre-test" the connection is that any error you'll get will be much more specific than the typical there was a problem connecting to the server.
Note that not all delay-inducing errors can be avoided. For example, if the DNS server is not responding, the resolver will typically wait 30 seconds before giving up. If an IP address is valid, but there's no machine with that address, attempting a connection will take a long time to fail. There's no way for the client to know there's no such machine; it could just be taking a long time to get a response.
I am trying to access the remote database from one Linux server to another which is connected via LAN.
but it is not working.. after some time it will generate an error
`_mysql_exceptions.OperationalError: (2003, "Can't connect to MySQL server on '192.168.0.101' (99)")'
this error is random it will raise any time.
each time create a new db object in all methods.
and close the connection as well then also why this error raise.
can any one please help me to sort out this problem
This issue is due to so many pending request on the remote database.
So in this situation MySql closes the connection to the running script.
to overcome this situation put
time.sleep(sec) # here int is a seconds in number that to sleep the script.
it will solve this issue.. without transferring database to local server or any other administrative task on mysql
My solution was to collect more queries for one commit statement if those were insert queries.
We moved our SQL Server 2005 database to a new physical server, and since then it has been terminating any connection that persist for 30 seconds.
We are experiencing this in Oracle SQL developer and when connecting from python using pyodbc
Everything worked perfectly before, and now python returns this error after 30 seconds:
('08S01', '[08S01] [FreeTDS][SQL Server]Read from the server failed (20004) (SQLExecDirectW)')
First of all what you need is profile the sql server to see if any activity is happening. Look for slow running queries, CPU and memory bottlenecks.
Also you can include the timeout in the querystring like this:
"Data Source=(local);Initial Catalog=AdventureWorks;Integrated Security=SSPI;Connection Timeout=30";
and extend that number if you want.
But remember "timeout" doesn't means time connection, this is just the time to wait while trying to establish a connection before terminating.
I think this problem is more about database performance or maybe a network issue.
Maybe check your remote query timeout? It should default to 600, but maybe it's set to 30? Info here