msgmap: speed up minmax with separate queries

This significantly improves the performance of the NNTP GROUP
command with 2.7 million messages from over 250ms to 700us.
SQLite is weird about this, but at least there's a way to
optimize it.

diff --git a/lib/PublicInbox/Msgmap.pm b/lib/PublicInbox/Msgmap.pm
index f5f88431bbfa82d1e7af847126d14441f6409864..feef8ba79ab9a657d8135b0c65ca0186dd7bed51 100644 (file)
--- a/lib/PublicInbox/Msgmap.pm
+++ b/lib/PublicInbox/Msgmap.pm
@@ -138,10 +138,14 @@ sub num_for {
 sub minmax {
        my ($self) = @_;
        my $dbh = $self->{dbh};
-       my $sth = $self->{num_minmax} ||=
-               $dbh->prepare('SELECT MIN(num),MAX(num) FROM msgmap');
+       # breaking MIN and MAX into separate queries speeds up from 250ms
+       # to around 700us with 2.7million messages.
+       my $sth = $dbh->prepare_cached('SELECT MIN(num) FROM msgmap', undef, 1);
        $sth->execute;
-        $sth->fetchrow_array;
+       my $min = $sth->fetchrow_array;
+       $sth = $dbh->prepare_cached('SELECT MAX(num) FROM msgmap', undef, 1);
+       $sth->execute;
+       ($min, $sth->fetchrow_array);
 }
 
 sub mid_prefixes {

diff --git a/t/perf-nntpd.t b/t/perf-nntpd.t
index 4987f98109b1c9e284bd6052daafbb69099f28db..e5021532096e3ed53ae7cf123d6b554d3ce02285 100644 (file)
--- a/t/perf-nntpd.t
+++ b/t/perf-nntpd.t
@@ -3,7 +3,7 @@
 use strict;
 use warnings;
 use Test::More;
-use Benchmark qw(:all);
+use Benchmark qw(:all :hireswallclock);
 use PublicInbox::Inbox;
 use File::Temp qw/tempdir/;
 use POSIX qw(dup2);
@@ -79,8 +79,13 @@ $s = IO::Socket::INET->new(%opts);
 $s->autoflush(1);
 my $buf = $s->getline;
 is($buf, "201 server ready - post via email\r\n", 'got greeting');
-ok($s->print("GROUP $group\r\n"), 'changed group');
-$buf = $s->getline;
+
+my $t = timeit(10, sub {
+       ok($s->print("GROUP $group\r\n"), 'changed group');
+       $buf = $s->getline;
+});
+diag 'GROUP took: ' . timestr($t);
+
 my ($tot, $min, $max) = ($buf =~ /\A211 (\d+) (\d+) (\d+) /);
 ok($tot && $min && $max, 'got GROUP response');
 my $nr = $max - $min;
@@ -100,7 +105,7 @@ sub read_until_dot ($) {
        $n;
 }
 
-my $t = timeit(1, sub {
+$t = timeit(1, sub {
        $s->print("XOVER $spec\r\n");
        $n = read_until_dot($s);
 });