Last modified: 2014-09-02 17:12:29 UTC
A cheap way to get information from page_props table for all links on page is needed. Two use cases are related to the DISPLAYTITLE: magic word (bug 17212) and to marking disambigs using the Disambiguator extension (bug 8339). At a glance it seems like it would be possible to reuse LinkCache + LinkBatch for both purposes, adding one indexed query per batch per prop, which sounds fast enough to me. (We'd also need a hook in both to allow extensions to do this.) The results could be stored in mGoodLinkFields in LinkCache, with names prefixed with "prop_" or something to distinguish them from the information from the page table that's in there right now. (This might require more hooks or not, depending on how we do them and how powerful we make them - if the hook for LinkCache allowed any queries, we'd need a separate one; if it just allowed stating prop names, it'd do here as well.) This really seems implementable and sort of easy. Thoughts? (CC-ing people involved in current patches to those two bugs and resident performance magicians.)
LinkCache is a kind of cache of last resort for parser linking, and could be removed without much performance impact. I think marking of links to disambiguation pages (bug 8339) should be handled in the same way as stub links. LinkHolderArray::replaceInternal() should do a batch query, and the result should be passed to Linker. There is an existing GetLinkColours hook, maybe that could be used. Ideally, the fixme comment on line 349 of LinkHolderArray.php should be fixed, i.e. clarifying the role of LinkCache and removing it from the data flow path from Parser to Linker. The issue with storing page_props data in a global-lifetime object like LinkCache is that it would use a lot of memory. LinkCache has no limit on the number of titles it holds, and it is difficult to implement such a limit due to the way it has historically been used. LinkHolderArray, by contrast, has a limited title count and its lifetime is limited to the length of the parse operation. Similarly, bug 17212 should be done with a batch query in CategoryViewer, similar to the treatment of the category table (cat_subcats etc.). It shouldn't be necessary to modify Linker in that case.
Today I learned of the GetLinkColours hook. That's good enough for me, and it's unclear how this bug could be fixed.
