[This should eventually be put into a section 5 manpage similar to our existing v1+v2 format manpages]
One feature I've been working on is detached/external indices for Xapian search. Currently (and since the earliest days of this project supporting Xapian), indices were per-inbox. This allowed inboxes to be isolated, making it easy to add and remove inboxes. The detached/external indices will allows a merging of several existing inboxes into a single (or several) virtual inboxes. Why? We want a cross-inbox search in the WWW UI, and perhaps an "All Mail" IMAP/JMAP inbox. Initial idea: We already use Xapian shards. Bump RLIMIT_NOFILE, put all the existing shards together, query, and done! Problem: Queries are unusably slow with hundreds of shards: https://lists.xapian.org/pipermail/xapian-discuss/2020-August/009815.html (and we'd expect hundreds of thousands of shards) Solution: Another index, independent of existing per-inbox indices. Sharded to CPU core count (similar to V2). over.sqlite3 is pretty useful for sharding + deduplication, so it will be used here, too. msgmap.sqlite3 may be optional, since its really only needed for NNTP... Existing public-inboxes can be attached to the new index. Detaching might not be supported right away... Downsides: More stuff to documente, more stuff for users to learn. Increased disk space and page cache utilization. Eventually, the web UI should be able to just use the detached index for search. Unfortunately, IMAP search relies on UIDs which are per-inbox, at least. Removing an inbox from the index can be tricky, will need a "GC" command. TBD: Unindexing from "public-inbox-learn spam" may be tricky. We need a way to prevent an untrusted inbox we're mirroring from unindexing a message that isn't marked as deleted from a "trusted" inbox. Purge + edit support will be similarly tricky, I think. We will probably require existing inboxes to have indexlevel=basic before an inbox can belong to a detached/external index. Advantages: Deduplication built-in. Cross-posted messages only get expensive Xapian data indexed once (multiple List-Id can get attached to each message). For users who can forgo per-inbox IMAP search, this may lead to space savings for WWW search with many inboxes. indexlevel=basic for NNTP and IMAP (w/o search) doesn't require too much space. Extra benefits of this approach: The potential to provide a transition from v1 to v2 inboxes by exposing them as a union of existing inboxes. "Private inbox" support with local flags (delete, seen, replied) Any number of virtual inboxes for grouping similar projects together can be created by combinations of existing v1/v2 inboxes. Disclaimer: My brain hasn't been working quite right... Heat + pandemic + power outages + insects + poor air quality have all been taking their toll :< -- unsubscribe: one-click, see List-Unsubscribe header archive: https://public-inbox.org/meta/
