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bug#32234: Cuirass: The SQLite built in busy handler might block the Fib

From: Ludovic Courtès
Subject: bug#32234: Cuirass: The SQLite built in busy handler might block the Fibers scheduler
Date: Mon, 23 Jul 2018 16:57:49 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

Clément Lassieur <address@hidden> skribis:

> Ludovic Courtès <address@hidden> writes:


>> Perhaps instead we need to set the timeout to a small value and handle
>> SQLITE_BUSY at the call site in our code.  We could define a macro that
>> automatically retries upon SQLITE_BUSY.
> That would limit the issue to the first timeout span: for that short
> time the scheduler would be blocked.  I think a timeout of 0 would be
> better.

Yes, 0 is an acceptable “small value.”  ;-)  Perhaps 100ms would be
acceptable if the situation is rare enough, dunno.

> Another solution would be to serialize all the database accesses as we
> do already with the url handler, and stop using the SQLITE
> multithreading features.  It would probably make the code simpler
> because we would use the same paradigm everywhere, and we would avoid
> looping until SQLITE isn't busy at each request.

In essence we’d introduce a “database server” running as a fiber, and
everyone would talk to that server.

I considered doing that before but then though sqlite would probably be
able to do better than this, but I don’t know.

What’s a bit annoying with switching to a database server model is that
we’d need to adapt every call site.



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