felace felace - 1 month ago 16
Python Question

Psycopg / Postgres : Connections hang out randomly

I'm using psycopg2 for the cherrypy app I'm currently working on and cli & phpgadmin to handle some operations manually. Here's the python code :

#One connection per thread
cherrypy.thread_data.pgconn = psycopg2.connect("...")
...
#Later, an object is created by a thread :
class dbobj(object):
def __init__(self):
self.connection=cherrypy.thread_data.pgconn
self.curs=self.connection.cursor(cursor_factory=psycopg2.extras.DictCursor)
...
#Then,
try:
blabla
self.curs.execute(...)
self.connection.commit()
except:
self.connection.rollback()
lalala
...
#Finally, the destructor is called :
def __del__(self):
self.curs.close()


I'm having a problem with either psycopg or postgres (altough I think the latter is more likely). After having sent a few queries, my connections drop dead. Similarly, phpgadmin -usually- gets dropped as well ; it prompts me to reconnect after having made requests several times. Only the CLI remains persistent.

The problem is, these happen very randomly and I can't even track down what the cause is. I can either get locked down after a few page requests or never really encounter anything after having requested hundreds of pages. The only error I've found in postgres log, after terminating the app is :

...
LOG: unexpected EOF on client connection
LOG: could not send data to client: Broken pipe
LOG: unexpected EOF on client connection
...


I thought of creating a new connection every time a new dbobj instance is created but I absolutely don't want to do this.

Also, I've read that one may run into similar problems unless all transactions are committed : I use the try/except block for every single INSERT/UPDATE query, but I never use it for SELECT queries nor do I want to write even more boilerplate code (btw, do they need to be committed ?). Even if that's the case, why would phpgadmin close down ?

max_connections is set to 100 in the .conf file, so I don't think that's the reason either. A single cherrypy worker has only 10 threads.

Does anyone have an idea where I should look first ?

Answer

Even tough I don't have any idea why successful SELECT queries block the connection, spilling .commit() after pretty much every single query that doesn't have to work in conjunction with another solved the problem.