Date: Sun, 31 Mar 2024 18:59:51 +0200
From: "Peter J. Holzer" <hjp-pgsql@hjp.at>
To: pgsql-general@lists.postgresql.org
Subject: Re: how to check if the license is expired.
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On 2024-03-30 09:23:15 -0400, Ron Johnson wrote:
> On Sat, Mar 30, 2024 at 9:15=E2=80=AFAM =E9=BB=84=E5=AE=81 <huangning0722=
@gmail.com> wrote:
>=20
>     I want to develop a postgresql paid extension, then there is a local
>     license file, how do I check if the license file is expired, check it=
 once
>     at each api execution, will that affect the performance of the api, is
>     there any other way?
>=20
>=20
> What you're really asking is "how do I read a file from an extension?".
> =C2=A0

We often chide users for falling into the "XY problem"[1] trap, so think
it's nice that =E9=BB=84=E5=AE=81 asks about the bigger picture.

I can't help with the extension (never wrote one), but a few thoughts:

Basically I see three ways to get at the license information:

* from a file (as mentioned)
* from a database table
* over the network (e.g. from a license server)

On my (not very fast) laptop I can open and read a small text file in
about 25 =C2=B5s. Selecting one row from a small database table takes about=
 100
=C2=B5s, which is quite a bit slower but I tested that from an external
process. A stored procedure would be faster than that and possibly even
faster than the file access. A query over the network is unlikely to be
faster.

Plus of course you need to check the contents, which likely involves
some cryptographic operation. Checking a 2048 bit RSA signature takes
about 30 =C2=B5s on my laptop, most other algorithms are slower (unless you
go with a simple HMAC which wouldn't be secure).

So realistically we are somewhere in the 50 to 200 =C2=B5s range.

Is this an acceptable performance penalty per API call? If not, is it
really necessary to check this on every call? Maybe it can be done just
once per session or once per hour.

        hp


[1] You have problem X and think that Y is part of the solution. So you
    ask how to achieve Y. However, Z would be better than Y for solving
    X, but nobody can tell you because they don't know about X.

--=20
   _  | Peter J. Holzer    | Story must make more sense than reality.
|_|_) |                    |
| |   | hjp@hjp.at         |    -- Charles Stross, "Creative writing
__/   | http://www.hjp.at/ |       challenge!"

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