https://bugzilla.wikimedia.org/show_bug.cgi?id=36400
Web browser: ---
Bug #: 36400
Summary: Continue may skip or repeat entries for iwlinks or
langlinks
Product: MediaWiki
Version: 1.20-git
Platform: All
OS/Version: All
Status: NEW
Keywords: patch-need-review
Severity: normal
Priority: Unprioritized
Component: API
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected]
Classification: Unclassified
Mobile Platform: ---
Created attachment 10495
--> https://bugzilla.wikimedia.org/attachment.cgi?id=10495
Patch to change the ORDER BY in the queries to match that expected by the
continue handling
For iwlinks, the continue parameter implies ORDER BY iwl_from, iwl_prefix,
iwl_title. However, this does not match the actual ordering in two of the three
cases:
1. When iwprefix is not given, the query is ORDER BY iwl_from, iwl_prefix (or
ORDER BY iwl_prefix when iwl_from is constant). iwl_title is not sorted, so if
the database would want to return three titles in the order A, C, B, with
iwlimit=1 it would return A and set continue to C. When continuing, it would
skip B because C > B.
2. When iwprefix is given but iwtitle is not given, the query is ORDER BY
iwl_title, iwl_from, which is backwards (iwl_prefix need not be included, as it
is constant). This is very easy to see the problem: just create pages A and B
where B has an interwiki link that sorts between two interwiki links in A.
https://en.wikipedia.org/w/api.php?format=jsonfm&action=query&prop=iwlinks&titles=A|C&iwprefix=wikisource&iwlimit=1
illustrates this at the moment.
3. When both iwprefix and iwltitle are specified, the query is ORDER BY
iwl_from. This is fine because iwl_prefix and iwl_title are constant in the
query.
The langlinks module has a similar structure, but here case 1 is not a problem
because (ll_from, ll_prefix) is a unique key. Case 2 *is* still an issue.
The simple fix would be to change the queries so the ordering matches that
implied by the continue parameter in all cases (see patch). I don't know if
this will make MySQL filesort, however.
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