-After using it for a while, my feeling is that hyperestradier, as used in
+After using it for a while, my feeling is that [[hyperestraier]], as used in
the [[plugins/search]] plugin, is not robust enough for ikiwiki. It doesn't
-upgrade well, and it has a habit of sig-11 on certian input from time to
+upgrade well, and it has a habit of sig-11 on certain input from time to
time.
So some other engine should be found and used instead.
does Lucene..) Another nice thing is it supports "more documents like this
one" kind of search. --[[Joey]]
+## xapian
+
+I've invesitgated xapian briefly. I think a custom xapian indexer and use
+of the omega for cgi searches could work well for ikiwiki. --[[Joey]]
+
+### indexer
+
+A custom indexer is needed because omindex isn't good enough for ikiwiki's
+needs for incremental rendering. (And because, since ikiwiki has page info
+in memory, it's silly to write it to disk and have omindex read it back.)
+
+The indexer would run as a ikiwiki hook. It needs to be passed the page
+name, and the content. Which hook to use is an open question.
+Possibilities:
+
+* `filter` - Since this runs before preprocess, only the actual text
+ written on the page would be indexed. Not text generated by directives,
+ pulled in by inlining, etc. There's something to be said for that. And
+ something to be said against it. It would also get markdown formatted
+ content, mostly, though it would still need to strip html.
+* `sanitize` - Would get the htmlized content, so would need to strip html.
+ Preprocessor directive output would be indexed.
+* `format` - Would get the entire html page, including the page template.
+ Probably not a good choice as indexing the same template for each page
+ is unnecessary.
+
+Currently, a filter hook seems the best option.
+
+The hook would remove any html from the content, and index it.
+It would need to add the same document data that omindex would, as well as
+adding the same special terms (see
+http://xapian.org/docs/omega/overview.html "Boolean terms").
+
+(Note that the U term is a bit tricky because I'll have to replicate
+ominxes's hash_string() to hash terms > 240 chars.)
+
+The indexer (and deleter) will need a way to figure out the ids in xapian
+of the documents to delete. One way is storing the id of each page in the
+ikiwiki index.
+
+The other way would be adding a special term to the xapian db that can be
+used with replace_document_by_term/delete_document_by_term. omindex uses
+U<url> as a term, and I guess I could just use that, and then map page
+names to urls when deleting a page ... only real problem being the
+hashing; a collision would be bad.
+
+At the moment, storing xapian ids in the ikiwiki index file seems like the
+best approach.
+
+The hook should try to avoid re-indexing pages that have not changed since
+they were last indexed. One problem is that, if a page with an inline is
+built, every inlined item will get each hook run. And so a naive hook would
+index each of those items, even though none of them have necessarily
+changed. Date stamps are one possibility. Another would be to avoid having
+the hook not do any indexing when `%preprocessing` is set (Ikiwiki.pm would
+need to expose that variable.) Another approach would be to use a
+needsbuild hook and only index the pages that are being built.
+
+#### cgi
+
+The cgi hook would exec omega to handle the searching, much as is done
+with estseek in the current search plugin.
+
+It would first set `OMEGA_CONFIG_FILE=.ikiwiki/omega.conf` ; that omega.conf
+would set `database_dir=.ikiwiki/xapian` and probably also set a custom
+`template_dir`, which would have modified templates branded for ikiwiki. So
+the actual xapian db would be in `.ikiwiki/xapian/default/`.
+
+## lucene
+
>> I've done a bit of prototyping on this. The current hip search library is [Lucene](http://lucene.apache.org/java/docs/). There's a Perl port called [Plucene](http://search.cpan.org/~tmtm/Plucene-1.25/). Given that it's already packaged, as `libplucene-perl`, I assumed it would be a good starting point. I've written a **very rough** patch against `IkiWiki/Plugin/search.pm` to handle the indexing side (there's no facility to view the results yet, although I have a command-line interface working). That's below, and should apply to SVN trunk.
>> Of course, there are problems. ;-)