Comment AI for debugging (Score 1) 248
Sometimes I use AI to write quick functions with bounds checking, it does a decent job, but it always needs tweaking.
AI shines for debugging, when I have something that "should" work, I copy/paste the errors or problem description into AI and ask "How to Fix ELI5"
Once, AI even suggested there was a bug in a library, and it was right.
Note: I pay for Google Gemini 2.5 Pro and find it the best for coding compared to Chat-GPT.
Gemini does a good job of breaking everything down.
Here is an example from a mysql session timeout (brokenpipe) a problem that I just fixed this morning, with the help of AI.
-- START Gemini Pro Session --
ELI5: Fixing "MySQL server has gone away (BrokenPipeError)"
The Problem Explained Like You're 5
Imagine you're on the phone with a friend (the MySQL server). You're talking, everything is fine. Then, you put the phone down for a while to do something else. Your friend, thinking you're done talking, hangs up. A little later, you pick up the phone and start talking again, but your friend is no longer there. All you hear is a dial tone. This is the "Broken pipe" or "MySQL server has gone away" error.
In your code, your application (you) was connected to the MySQL database (your friend). It kept the connection open in a "pool" of connections to be reused, which is efficient. However, the connection sat idle for too long, and the MySQL server, to save resources, automatically disconnected it (hung up). When your application tried to use that same connection again, it discovered the connection was dead, leading to the error.
This specific error trace shows that SQLAlchemy, a tool that helps your Python code talk to the database, tried to clean up (rollback a transaction) on a connection that had already been dropped by the server.
The Fix: How to Keep the Conversation Going
The most common and effective way to fix this is to tell SQLAlchemy to check if the connection is still alive before using it, or to regularly refresh the connection. Here are the recommended solutions, from most common to more specific:
1. Recycle Connections (pool_recycle) - The "Hang Up and Redial" Approach
This is the most common and generally recommended fix. You can tell SQLAlchemy to automatically close and replace connections that have been open for a certain amount of time. This time should be less than the MySQL server's wait_timeout (which is often 8 hours by default, but can be much shorter on some hosting providers). A safe value is often 3600 seconds (1 hour) or less.
When you create your SQLAlchemy engine, add the pool_recycle argument:
Python
from sqlalchemy import create_engine
# Add pool_recycle to your engine creation
engine = create_engine(
"mysql+pymysql://user:password@host/dbname",
pool_recycle=3600
)
2. Pre-Ping Connections (pool_pre_ping) - The "Are You Still There?" Check
This option tells SQLAlchemy to send a very small, quick message (a "ping") to the database to see if the connection is still active before your application uses it. If the ping fails, SQLAlchemy will replace the dead connection with a new one. This is very reliable but adds a tiny bit of overhead to each database operation.
Python
from sqlalchemy import create_engine
# Add pool_pre_ping to your engine creation
engine = create_engine(
"mysql+pymysql://user:password@host/dbname",
pool_pre_ping=True
)
For many applications, pool_pre_ping=True is the most robust solution.
3. Adjusting Server-Side Timeouts (If you control the server)
If you have administrative access to your MySQL server, you can increase its wait_timeout value. This tells the server to wait longer before hanging up on idle connections. You would typically change this in your MySQL configuration file (my.cnf or my.ini).
[mysqld]
wait_timeout = 28800
After changing this, you must restart the MySQL server. However, it's often better to make your application more resilient (using pool_recycle or pool_pre_ping) than to rely on server-side settings.
4. For Large Queries: Check max_allowed_packet
Less commonly, this error can occur if you are trying to send a very large piece of data to the database that exceeds the server's max_allowed_packet size. If you are inserting or updating a row with a lot of text or a large binary file, and the error happens consistently with that operation, you may need to increase this value in your MySQL server's configuration file.
[mysqld]
max_allowed_packet=64M
Again, this requires server access and a restart of the MySQL service.
Summary
In most cases, the simplest and most effective way to fix the "MySQL server has gone away" error is to configure SQLAlchemy's connection pool to handle stale connections gracefully. Start by adding pool_pre_ping=True or a reasonable pool_recycle value to your create_engine call. This ensures your application doesn't try to talk on a dead line.
