[Moin-user] Very slow page saving caused by notifications

[Thomas Waldmann]

> There are probably other areas of Moin that could benefit from Xapian-based 
> indexing, but this certainly looks like a good application of it.

Some notes:

search / indexing
=================

xapian is not a requirement for moin 1.9, but an option. thus, there is
alternative code in moin (for searching) so it works if you do not have
xapian.

xapian is a binary dependency - you either need a package or a compiler.

due to the 2 distinct codes (indexed vs. non-indexed) for searching with
and without xapian, there are some fundamental differences in how one
can use it and what one can expect from it.

in moin 2, we have replaced xapian by whoosh (which is pure-python, so
we were able to just REQUIRE it). this will fix quite some of the issues
we have seen in moin 1.x relating to indexing, queries and search.

i have done a few benchmarks and whoosh was surprisingly fast (not as
fast as xapian sometimes, but also not much slower).

in moin2, we use whoosh for all sorts of internal lookups as well as for
the search you can do from the UI.

all stuff (users, pages, attachments) in moin2 is stored into typed
items/revisions (which have metadata and data) and metadata and
(filtered) data gets indexed.

that makes life much easier for the developers as there is less and
simpler code now.

caching
=======
sometimes stuff can be accelerated by adding a cache. but if you have a
cache, you always have to make sure it is consistent with the real data.

i had a quick look at the subscribed users caching patch and I suspect
that might not be the case there.