https://bugzilla.wikimedia.org/show_bug.cgi?id=21868
Summary: SMW Parser is missing grammar validation
Product: MediaWiki extensions
Version: any
Platform: All
OS/Version: All
Status: NEW
Severity: critical
Priority: Normal
Component: Semantic MediaWiki
AssignedTo: mar...@semantic-mediawiki.org
ReportedBy: avino...@gmail.com
The SMW Parser seems to ignore grammar/syntax errors altogether. Instead of
issuing an error message, it's generating an impossibly-heavy DB query:
SELECT /* SMW::getQueryResult Avinoamr */ DISTINCT t0.smw_id AS
id,t0.smw_title AS t,t0.smw_namespace AS ns,t0.smw_iw AS iw,t0.smw_sortkey
FROM `smw_ids` AS t0 INNER JOIN `smw_ids` AS t2 ON t0.smw_id=t2.smw_id WHERE
t2.smw_iw!=':smw' AND t2.smw_iw!=':smw-redi' AND t2.smw_iw!=':smw-border' AND
t2.smw_iw!=':smw-intprop' ORDER BY t0.smw_sortkey ASC LIMIT 21
This query is obviously malformed, it doesn't try to match anything useful,
just filters out certain rows. On our current MediaWiki installation this query
takes more than 1 hour to complete.
I've noticed it's being generated by (1) using a bad syntax (try
[Field::->Value]]), or (2) by using the {#ask} parser function with an empty
query string (try {#ask:}).
Obviously, the user should be aware of what he's doing - but a couple of these
queries can really slow down the DBs for no reason.
I think it's a critical performance/stability bug. If I'm not mistaken, a
single user can pretty much crash several of the DB servers simply by running
these queries repeatedly.
I'm not certain what kind of parsing algorithm is being used (LL(1) ?), but I'm
sure grammar validation is part of it. If you wish, I volunteer to help with
developing this support - but I'd like to have a comprehensive understanding
and guidance before I begin.
By the way - another approach would be to check the Query object before
executing it. And if we realize that this meaningless SQL error will be
executed, we can just throw a non-informative Parsing exception. That's a more
quick & dirty solution, in my opinion.
--
Configure bugmail: https://bugzilla.wikimedia.org/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.
_______________________________________________
Wikibugs-l mailing list
Wikibugs-l@lists.wikimedia.org
https://lists.wikimedia.org/mailman/listinfo/wikibugs-l
