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, 4 insertions, 1 deletions

diff --git a/lib/PublicInbox/Search.pm b/lib/PublicInbox/Search.pm
index 7e72913f..ba239255 100644
--- a/lib/PublicInbox/Search.pm
+++ b/lib/PublicInbox/Search.pm
@@ -55,7 +55,7 @@ use constant {
 use PublicInbox::Smsg;
 use PublicInbox::Over;
 our $QP_FLAGS;
-our %X = map { $_ => 0 } qw(BoolWeight Database Enquire QueryParser Stem);
+our %X = map { $_ => 0 } qw(BoolWeight Database Enquire QueryParser Stem Query);
 our $Xap; # 'Search::Xapian' or 'Xapian'
 our $NVRP; # '$Xap::'.('NumberValueRangeProcessor' or 'NumberRangeProcessor')
 our $ENQ_ASCENDING;
@@ -331,6 +331,9 @@ sub has_threadid ($) {
 sub _enquire_once { # retry_reopen callback
         my ($self, $query, $opts) = @_;
         my $xdb = xdb($self);
+        if (defined(my $eidx_key = $opts->{eidx_key})) {
+                $query = $X{Query}->new(OP_FILTER(), $query, 'O'.$eidx_key);
+        }
         my $enquire = $X{Enquire}->new($xdb);
         $enquire->set_query($query);
         $opts ||= {};