using postgresql for session

On Wed, 7 Oct 2015 09:58:04 -0600
"john.tiger" <john.tigernassau@gmail.com> wrote:

has anyone used postgres jsonb for holding session ? Since server side
session is really just a piece of data, why bother with special
"session" plugins and just use postgres to hold the data and retrieve it
with psycopg2 ? Maybe use some trigger if session changes? We are
using python Bottle with psycopg2 (super simple, powerful combo) - are
we missing something magical about session plugins ?

Nothing that I'm aware of. I've worked on large projects that keep the
session data in a Postgres table with great success.

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Bill Moran

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On 10/07/2015 08:58 AM, john.tiger wrote:

has anyone used postgres jsonb for holding session ? Since server side
session is really just a piece of data, why bother with special
"session" plugins and just use postgres to hold the data and retrieve it
with psycopg2 ?

That is how Django does it. It uses the django_session table.

Maybe use some trigger if session changes?

That would seem to the tricky part, determining when a session changes.

We are

using python Bottle with psycopg2 (super simple, powerful combo) - are
we missing something magical about session plugins ?

What sort of plugin are you talking about?

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Adrian Klaver
adrian.klaver@aklaver.com

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On 10/07/2015 10:53 AM, Bill Moran wrote:

On Wed, 7 Oct 2015 09:58:04 -0600
"john.tiger" <john.tigernassau@gmail.com> wrote:

has anyone used postgres jsonb for holding session ? Since server side
session is really just a piece of data, why bother with special
"session" plugins and just use postgres to hold the data and retrieve it
with psycopg2 ? Maybe use some trigger if session changes? We are
using python Bottle with psycopg2 (super simple, powerful combo) - are
we missing something magical about session plugins ?

Nothing that I'm aware of. I've worked on large projects that keep the
session data in a Postgres table with great success.

Previous job gave up on mongo and switched to postgres since it was
faster, more reliable.

On Oct 7, 2015, at 11:58 AM, john.tiger wrote:

has anyone used postgres jsonb for holding session ? Since server side session is really just a piece of data, why bother with special "session" plugins and just use postgres to hold the data and retrieve it with psycopg2 ? Maybe use some trigger if session changes? We are using python Bottle with psycopg2 (super simple, powerful combo) - are we missing something magical about session plugins ?

I previously used TEXT or BLOB for holding session data, and pickled the data. I can't remember.

If you're going to use PostgresSQL for the session, the big performance tip is to use partial index on the session key (assuming it's an md5-like hash).

So you'd want a table that is something like this:

CREATE TABLE session(
session_id VARCHAR(32) PRIMARY KEY,
session_data TEXT
);
CREATE INDEX idx_session_partial ON session(substr(session_id , 0,5))

Then query like this

SELECT * FROM session WHERE session_id = :session_id AND substr(session_id, 0, 5) = :session_id_substring ;
SELECT * FROM session WHERE session_id = :session_id AND substr(session_id, 0, 5) = substr(:session_id, 0, 5) ;

That will get the planner to use the partial index first, before using the session_id index. Depending on how many items are in your table, it can make your SELECTS several orders of magnitude faster.

As for session plugins -- a lot of people in the web frameworks community are abandoning server side sessions for client side sessions. They are generally easier to handle state across clusters and data centers. Some server side session-like data is still needed, but it's often assembled from data in the client side.

Most of the Python session plugins I've used have some sort of status check coupled with a cleanup function/middleware component to see if the object has changed at all. This way UPDATES only occur when needed.

FWIW, I ended up migrating our sessions into redis. We already had redis running on the cluster, and offloading it got a lot more performance our Postgres without scaling our hardware. There just isn't much of a reason for having pg manage a simple KV store.

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maybe we will just use beaker with our bottle framework - thought it was duplicative to have redis since we have postgres and lookup speed should be  trivial since session only has a couple of small fields like account id and role

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On 10/14/15 8:57 PM, Tiger Nassau wrote:

maybe we will just use beaker with our bottle framework - thought it was
duplicative to have redis since we have postgres and lookup speed should
be trivial since session only has a couple of small fields like account
id and role

The problem with sessions in Postgres tends to be the update rate, since
every update results in a new table tuple, and possible new index
tuples. That gets painful really fast for high-update workloads.
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Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com

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