nntp: make XOVER, XHDR, OVER, HDR and NEWNEWS faster

While SQLite is faster than Xapian for some queries we
use, it sucks at handling OFFSET.  Fortunately, we do
not need offsets when retrieving sorted results and
can bake it into the query.

For inbox.comp.version-control.git (v1 Xapian),
XOVER and XHDR are over 20x faster.

1 files changed, 18 insertions, 21 deletions

diff --git a/lib/PublicInbox/NNTP.pm b/lib/PublicInbox/NNTP.pm
index 48ab7fc2..ff6d8958 100644
--- a/lib/PublicInbox/NNTP.pm
+++ b/lib/PublicInbox/NNTP.pm
@@ -331,20 +331,20 @@ sub cmd_newnews ($$$$;$$) {
         };
         return '.' unless @srch;
 
-        my $opts = { limit => 1000, offset => 0 };
+        my $prev = 0;
         long_response($self, 0, long_response_limit, sub {
                 my ($i) = @_;
                 my $srch = $srch[0];
-                my $msgs = $srch->query_ts($ts, $opts);
-                if (my $nr = scalar @$msgs) {
+                my $msgs = $srch->query_ts($ts, $prev);
+                if (scalar @$msgs) {
                         more($self, '<' .
                                 join(">\r\n<", map { $_->mid } @$msgs ).
                                 '>');
-                        $opts->{offset} += $nr;
+                        $prev = $msgs->[-1]->{num};
                 } else {
                         shift @srch;
                         if (@srch) { # continue onto next newsgroup
-                                $opts->{offset} = 0;
+                                $prev = 0;
                         } else { # break out of the long response.
                                 $$i = long_response_limit;
                         }
@@ -582,7 +582,7 @@ sub long_response ($$$$) {
         $self->{long_res} = sub {
                 # limit our own running time for fairness with other
                 # clients and to avoid buffering too much:
-                my $lim = 100;
+                my $lim = $end == long_response_limit ? 1 : 100;
 
                 my $err;
                 do {
@@ -710,20 +710,19 @@ sub hdr_searchmsg ($$$$) {
                 return $r unless ref $r;
                 my ($beg, $end) = @$r;
                 more($self, $xhdr ? r221 : r225);
-                my $off = 0;
-                long_response($self, $beg, $end, sub {
+                my $cur = $beg;
+                long_response($self, 0, long_response_limit, sub {
                         my ($i) = @_;
-                        my $msgs = $srch->query_xover($beg, $end, $off);
-                        my $nr = scalar @$msgs or return;
-                        $off += $nr;
+                        my $msgs = $srch->query_xover($cur, $end);
+                        my $nr = scalar @$msgs or
+                                        return ($$i = long_response_limit);
                         my $tmp = '';
                         foreach my $s (@$msgs) {
                                 $tmp .= $s->num . ' ' . $s->$field . "\r\n";
                         }
                         utf8::encode($tmp);
                         do_more($self, $tmp);
-                        # -1 to adjust for implicit increment in long_response
-                        $$i = $nr ? $$i + $nr - 1 : long_response_limit;
+                        $cur = $msgs->[-1]->{num} + 1;
                 });
         }
 }
@@ -848,20 +847,18 @@ sub cmd_xover ($;$) {
         my ($beg, $end) = @$r;
         more($self, "224 Overview information follows for $beg to $end");
         my $srch = $self->{ng}->search;
-        my $off = 0;
-        long_response($self, $beg, $end, sub {
+        my $cur = $beg;
+        long_response($self, 0, long_response_limit, sub {
                 my ($i) = @_;
-                my $msgs = $srch->query_xover($beg, $end, $off);
-                my $nr = scalar @$msgs or return;
-                $off += $nr;
+                my $msgs = $srch->query_xover($cur, $end);
+                my $nr = scalar @$msgs or return ($$i = long_response_limit);
 
                 # OVERVIEW.FMT
                 more($self, join("\r\n", map {
                         over_line($_->{num}, $_);
                         } @$msgs));
-
-                # -1 to adjust for implicit increment in long_response
-                $$i = $nr ? $$i + $nr - 1 : long_response_limit;
+                $cur = $msgs->[-1]->{num} + 1;
+                1;
         });
 }