Questions on size of session

[Timin Uram]

Hey! Is there some sort of limit on how much one could store in a
session as far as amount of data?

Is it advisable to store a LOT of data in the session when a user logs
in to save queries to the dbase while the user is browsing the site?

Does this depend somehow on how many sessions are going on at once?

Any input would be appreciated, thanks!

[Tony Marston]

There is really no limit to the size of session data, but I would strongly
advise AGAINST storing large volumes of table data in a session array to
avoid reading from the database again. That is NOT what sessions ere
designed for. You should only store in the session array what is necessary
to maintain state between requests. If other data can be read from the
database, then read it from the database. There will be little or no
difference in performance.

--
Tony Marston

http://www.tonymarston.net
"Timin Uram" <so*******@hotmail.com> wrote in message
news:11**********************@z14g2000cwz.googlegr oups.com...

Hey! Is there some sort of limit on how much one could store in a
session as far as amount of data?

Is it advisable to store a LOT of data in the session when a user logs
in to save queries to the dbase while the user is browsing the site?

Does this depend somehow on how many sessions are going on at once?

Any input would be appreciated, thanks!

[Erwin Moller]

Timin Uram wrote:

Hey! Is there some sort of limit on how much one could store in a
session as far as amount of data?
No, session are stored (serialized $_SESSION) as flatfile or in a database.
So the limit depends on the size on your system.

Is it advisable to store a LOT of data in the session when a user logs
in to save queries to the dbase while the user is browsing the site?
In general: No.
It is advisable to store a few essential pieces of information in your
session, and query your database when needed, based on these values.
eg: suppose you have a huge usertable (including adresses and such)

when user logs in:
$_SESSION["userid"] = $someuserid;
and maybe:
$_SESSION["username"] = $someusername;

Like that you can easily say:
hello <?= $_SESSION["username"] ?>, welcome here and there.

But you typically do not store everything you know of the user in a SESSION,
because userid is enough for you to fetch the information when you need it.


Does this depend somehow on how many sessions are going on at once?
Yes.
If you have 1 MB per session, 1000 session will clearly give you some
performancepenalty.


Any input would be appreciated, thanks!

However: I have been in situation I used a session to store a huge amount of
information.
In that particular situation, I calculated all the information I needed for
a complex image, and then had to feed it to an imagecreationscript.
That image was on the same page as where all the calculation were performed.
But the imageproducing script was a seperate script, so it needed the
information too.
So I stored in in a session.
After the imagescript was done, it deleted the information from the session.

Bottomline: Avoid storing unneeded information in a session.
Unneeded as in: I can fetch it quickly when needed based on a userid or
something like that.

just my 2 cents.

Regards,
Erwin Moller

[chernyshevsky]

No, it's not advisable to store a lot of data in a session. As others
have noted, it's not a idea to duplicate data from a database. Even if
you really need some sort of caching mechanism, you wouldn't store the
data in a session. The problem is that PHP rewrites the session data
for every request. And as we all know writing to disk is a rather slow
operation.

If you really need to do it, serialize the array and store it in a
separate file.

[Erwin Moller]

ch***********@hotmail.com wrote:

No, it's not advisable to store a lot of data in a session. As others
have noted, it's not a idea to duplicate data from a database. Even if
you really need some sort of caching mechanism, you wouldn't store the
data in a session. The problem is that PHP rewrites the session data
for every request. And as we all know writing to disk is a rather slow
operation.

If you really need to do it, serialize the array and store it in a
separate file.

Just curious: Isn't that excactly what a session does between request?
I mean: Isn't that excactly as slow as storing it in a session?

Regards,
Erwin Moller

[Erwin Moller]

Erwin Moller wrote:

ch***********@hotmail.com wrote:

No, it's not advisable to store a lot of data in a session. As others
have noted, it's not a idea to duplicate data from a database. Even if
you really need some sort of caching mechanism, you wouldn't store the
data in a session. The problem is that PHP rewrites the session data
for every request. And as we all know writing to disk is a rather slow
operation.

If you really need to do it, serialize the array and store it in a
separate file.

Just curious: Isn't that excactly what a session does between request?
I mean: Isn't that excactly as slow as storing it in a session?

Aha, I think understand what you mean:
If you need that bunch of serialized data only 1 in 10 pages, you only
unpack it once in 10 pages.
Session is of course packing/unpacking for every request.

doh...

*Erwin runs off to find some coffee*

Regards,
Erwin Moller