isearch: emulate per-inbox search with ->ALL

Using "eidx_key:" boolean prefix to limit results to a given
inbox, we can use ->ALL to emulate and replace per-Inbox
xap15/[0-9] search indices.

With this change, the presence of "extindex.all.topdir" in the
$PI_CONFIG will cause the WWW code to use that extindex and
ignore per-inbox Xapian DBs in xap15/[0-9].

Unfortunately IMAP search still requires old per-inbox indices,
for now.  Mapping extindex Xapian docids to per-Inbox UIDs and
vice-versa is proving tricky.  Fortunately, IMAP search is
rarely used and optional.  The RFCs don't specify expensive
phrase search, either, so `indexlevel=medium' can be used in
per-inbox Xapian indices to save space.

For primarily WWW (and future JMAP) users; this should result in
significant disk space, FD, and page cache footprint savings for
large instances with many inboxes and many cross-posted
messages.

1 files changed, 1 insertions, 0 deletions

diff --git a/lib/PublicInbox/ExtSearch.pm b/lib/PublicInbox/ExtSearch.pm
index 80455d8d..2a560935 100644
--- a/lib/PublicInbox/ExtSearch.pm
+++ b/lib/PublicInbox/ExtSearch.pm
@@ -128,5 +128,6 @@ no warnings 'once';
 *recent = \&PublicInbox::Inbox::recent;
 
 *max_git_epoch = *nntp_usable = *msg_by_path = \&mm; # undef
+*isrch = *search;
 
 1;