I've set up PGBouncer and configured it to connect to my postgres DB and it all connects just fine, however I'm not sure if its actually working.
I have a php script that runs as a daemon and picks up beanstalk jobs. The problem is for every distinct user/action on the system it opens a new connection to postgres and then leaves that connection idling because the daemon doesn't actually stop running so the connection is never terminated (a quick fix for this was to reset the connection at the end of the script loop, but that is going to be inefficient with many connects).
Anyway, this caused postgres to eventually run out of connections and lock up...
So PGBouncer seems like the answer.
But now when I run it, I see the same db connection multiple times when i do ps ax | grep postgres.
Isn't PGBouncer supposed to only ever have 1 connection open to the DB and route all traffic through that connection? Then open a new connection if that one is full?
At present I have 3 for one db connection (my access control system) and 2 for the other database (my client specific data).
To me, it feels like if I roll out these changes then I will just be faced with the same problem that the connections will just get eaten up again because they're not being released.
I hope that explains enough for someone to offer any advice.
It sounds like an important step here is to fix the scripts so they release the connections when they're done. Once you do that, PgBouncer will help reduce the connection setup/teardown overhead, but in connection pooling mode it won't give you the ability to maintain more connections to Pg than you otherwise could.
However, you can also use PgBouncer in transaction-pooling mode. When used for transaction pooling, PgBouncer keeps a pool of idle backend transactions and only assigns them when a client does a BEGIN. Connections are returned to the pool after the client does a COMMIT or ROLLBACK. That means that in transaction pooling mode you can have large numbers of open connections to PgBouncer; they don't each need a corresponding connection to a PostgreSQL backend, so long as most of them are idle at any point in time and don't have any transaction open.
The only real downside of transaction pooling mode is that it breaks applications that expect to SET session-level variables, keep prepared statements across transactions, etc. Applications may need modification, e.g. to use SET LOCAL.
Related
in Java, application servers like JBoss EAP have the option to periodically verify the connections in a database pool (https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/6.4/html/administration_and_configuration_guide/sect-database_connection_validation). This has been very useful for removing stale connections.
I'm now looking at a ADO.NET application, and I was wondering if there was any similar functionality that could be used with a Microsoft SQL Server?
I ended up find this post by redgate that describes some of the validation that goes on when connections are taken from the pool:
If the connection has died because a router has decided that it no
longer wants to forward your packets and no other routers like you
either then there is no way to know this unless you try to send some
data and don’t get a response.
If you create a connection and a connection pool is created and
connections are put into the pool and not used, the longer they are in
there, the bigger the chance of something bad happening to it.
When you go to use a connection there is nothing to warn you that a
router has stopped forwarding your packets until you go to use it; so
until you use it, you do not know that there is a problem.
This was an issue with connection pooling that was fixed in the first
.Net 4 reliability update (see issue 14 which vaguely describes this)
with a feature called “Connection Pool Resiliency”. The update meant
that when a connection is about to be taken from the pool, it is
checked for TCP validity and only returned if it is in a good state.
i connect to Postgresql via JDBC through pgbouncer with transaction pooling mode enabled. As far as I know in this mode pgbouncer can share same connection for several client without breaking session. So several clients may work within a single session sequentially, one by another. The question is does pgbouncer care about reseting session parameters when it detach one client from a connection and attach another client to this connection?
In particular, my app get connection and then issues something like this:
executeQuery(connection,"select set_config('myapp.user','fonar101',false)");
..../*other actions*/
commit(connection);
After commit pgbouncer can detach my app from connection and get it back to its pool, right? So,
if I issue another statements after commit they will probably be
executed within another session with incorrect values of session
parameters
pgbouncer can attach another client to that connection
and that client will proceed with again incorrect session settings
How does pgbouncer care about this things?
I'd say the opposite:
https://pgbouncer.github.io/config.html
transaction
Server is released back to pool after transaction finishes.
Which means that when you SET SESSION (default for SET), without specifying SET LOCAL, you change settings for all transactions that share the session in the pool...
According pgbouncer docs it doesnt support SET/RESET and ON COMMIT DROP for temp tables in transaction pooling mode.
When I run a query that takes a long time on my Postgres server (maybe 30 minutes), I get the error. I've verified the query is running with active status on the server using pgAdmin. I've also verified the correctness of the query, as it runs successfully on a smaller dataset. Server configurations are default, I haven't changed anything. Please help!
Look into the PostgreSQL server log.
Either you'll find a crash report there, which would explain the broken connection, or there is something in your network that cuts connections with no activity after a while.
Investigate your firewalls!
Maybe it is a solution to set the configuration parameter tcp_keepalives_idle to a value shorter than the time when the connection is cut. That will cause the server operating system to send keepalive messages on idle connections, which may be enough to prevent the overzealous connection reaper in your environment from disrupting your work.
In Postgres, is there a one-to-one relationship between a client and a connection? In other word, is a client always one connection and no client can open more than one connection?
For example, when Postgres says:
org.postgresql.util.PSQLException: FATAL: sorry, too many clients already.
is that equivalent to "too many connections already"?
Also, as far as I understand, Postgres uses one process for each client. So does this mean that each process is used for one connection only?
Refer - https://www.postgresql.org/docs/9.6/static/connect-estab.html
PostgreSQL is implemented using a simple "process per user"
client/server model. In this model there is one client process
connected to exactly one server process. As we do not know ahead of
time how many connections will be made, we have to use a master
process that spawns a new server process every time a connection is
requested.
So yes, one server process serves one connection.
You can have as many connections from a single client (machine, application) as the server can manage. The server can support a given number of connections, whether or not these come from different clients (machine, application) is irrelevant to the server.
The connection is made to the postmaster process that is listening on the port that PG is configured to listen to (5432 by default). When a connection is established (after authentication), the server spawns a process which is used exclusively by a single client. That client can make multiple connections to the same server, for instance to connect to different databases, or the same database using different credentials, etc.
This question already has answers here:
Is there a timeout for idle PostgreSQL connections?
(7 answers)
Closed 8 years ago.
I had a user who was having a crashing issue with our app and was not closing his connection to the database properly - eventually reaching his connection limit and was unable to log back in.
That's ok. The problem was eventually fixed and the app is closing the connection properly now.
I was wondering, if a user reaches his connection limit, and without me doing anything, what is the default setting for Postgres 9.1 to drop the connection on its own?
Well, for your actual question:
if a user reaches his connection limit, and without me doing anything, what is the default setting for Postgres 9.1 to drop the connection on its own?
If the connections you are talking about are active connections to real clients (i.e. the client is still around, not crashed and exited, and can read and write to its connection socket), Postgres will not "drop the connection on its own". See this question if you're interested in ways to prune such idle clients.
On the other hand, it is possible for a Postgres backend to be nominally connected to a client which has really crashed or otherwise exited, as you alluded to earlier. In that case, Postgres may not notice the client is gone and not just in an idle state for some time. I believe the exact time would be controlled by a "TCP keepalive time" OS setting, or you could even fiddle with this setting in your client via connection parameters: see the various keepalives-related settings.