Storage Engines

Every time you login to Telegram, some personal piece of data are created and held by both parties (the client, Pyrogram and the server, Telegram). This session data is uniquely bound to your own account, indefinitely (until you logout or decide to manually terminate it) and is used to authorize a client to execute API calls on behalf of your identity.

Persisting Sessions

In order to make a client reconnect successfully between restarts, that is, without having to start a new authorization process from scratch each time, Pyrogram needs to store the generated session data somewhere.

Other useful data being stored is peers’ cache. In short, peers are all those entities you can chat with, such as users or bots, basic groups, but also channels and supergroups. Because of how Telegram works, a unique pair of id and access_hash is needed to contact a peer. This, plus other useful info such as the peer type, is what is stored inside a session storage.

So, if you ever wondered how is Pyrogram able to contact peers just by asking for their ids, it’s because of this very reason: the peer id is looked up in the internal database and the available access_hash is retrieved, which is then used to correctly invoke API methods.

Different Storage Engines

Let’s now talk about how Pyrogram actually stores all the relevant data. Pyrogram offers two different types of storage engines: a File Storage and a Memory Storage. These engines are well integrated in the library and require a minimal effort to set up. Here’s how they work:

File Storage

This is the most common storage engine. It is implemented by using SQLite, which will store the session and peers details. The database will be saved to disk as a single portable file and is designed to efficiently store and retrieve peers whenever they are needed.

To use this type of engine, simply pass any name of your choice to the session_name parameter of the Client constructor, as usual:

from pyrogram import Client

with Client("my_account") as app:
    print(app.get_me())

Once you successfully log in (either with a user or a bot identity), a session file will be created and saved to disk as my_account.session. Any subsequent client restart will make Pyrogram search for a file named that way and the session database will be automatically loaded.

Memory Storage

In case you don’t want to have any session file saved to disk, you can use an in-memory storage by passing the special session name “:memory:” to the session_name parameter of the Client constructor:

from pyrogram import Client

with Client(":memory:") as app:
    print(app.get_me())

This storage engine is still backed by SQLite, but the database exists purely in memory. This means that, once you stop a client, the entire database is discarded and the session details used for logging in again will be lost forever.

Session Strings

In case you want to use an in-memory storage, but also want to keep access to the session you created, call export_session_string() anytime before stopping the client…

from pyrogram import Client

with Client(":memory:") as app:
    print(app.export_session_string())

…and save the resulting (quite long) string somewhere. You can use this string as session name the next time you want to login using the same session; the storage used will still be completely in-memory:

from pyrogram import Client

session_string = "...ZnUIFD8jsjXTb8g_vpxx48k1zkov9sapD-tzjz-S4WZv70M..."

with Client(session_string) as app:
    print(app.get_me())

Session strings are useful when you want to run authorized Pyrogram clients on platforms like Heroku, where their ephemeral filesystems makes it much harder for a file-based storage engine to properly work as intended.

But, why is the session string so long? Can’t it be shorter? No, it can’t. The session string already packs the bare minimum data Pyrogram needs to successfully reconnect to an authorized session, and the 2048-bits auth key is the major contributor to the overall length. Needless to say that this string, as well as any other session storage, represent strictly personal data. Keep them safe.