[Koha-bugs] [Bug 8970] MARC import gives error under Starman/Plack

[bugzilla-daemon at bugs.koha-community.org]

http://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=8970

--- Comment #20 from Jacek Ablewicz <abl at biblos.pk.edu.pl> ---
(In reply to Robin Sheat from comment #17)
> OK, while I haven't nailed this down exactly, I think I have some hints that
> there's a race condition happening. I also get plain weird things like:
> 
> DBD::mysql::db selectrow_array failed: Cannot add or update a child row: a
> foreign key constraint fails (`koha_test`.`import_biblios`, CONSTRAINT
> `import_biblios_ibfk_1` FOREIGN KEY (`import_record_id`) REFERENCES
> `import_records` (`import_record_id`) ON DELETE CASCADE ON UPDATE CASCADE)
> at /mnt/catalyst/koha/C4/Context.pm line 618.
> 

Looks like the plack/mod_perl related pitfall, when 2+ concurrently running
processes are sharing the same single DBI connection (a big no-no, DBI would
not work reliably if used that way). But - reading previous comments in this
report, there may be some other unrelated/additional problems with background
jobs under plack as well (?).

> and that line in C4::Context is requesting a preference. So I think that we
> have some sort of race condition going on. Also, forking a plack process is
> a) tricky, and b) memory heavy (which is why the fork was failing for me in
> the first instance, it started working when I changed my VM from 512MB to
> 1024MB.)

Forked/background jobs - and plack workers etc. - would not be as memory heavy
(thanks to copy-on-write kernel feature) if we preload more C4/*, Koha/* and
CPAN modules at plack startup script. But right now, preloading C4/Auth.pm, or
any other module which is using it would cause the same exact problem with
single DBI connection being shared between all plack workers and/or mod-perl
processes.. That's because C4/Auth is fetching some sysprefs in BEGIN {} block.
I addressed it with the following line added in the end of the startup script

   ${C4::Context::context}->{dbh}=undef;

It seems to work fine under mod_perl (but I haven't tested it all that much
yet,
in particular - not with plack). This start-up script:

...

use CGI ();
CGI->compile(':all');

use C4::Members ();
use C4::Search ();
use C4::Serials ();
use C4::Acquisition ();
use C4::AuthoritiesMarc ();

C4::Context->config('AaaBbCcc');
${C4::Context::context}->{dbh}=undef;

does preload circa 80% of C4/* perl code, resulting in significantly better
latency and total RAM usage under mod_perl.

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