[PATCH 1/2] searchidxshard: ensure we set indexlevel on shard[0]

[Eric Wong <e@yhbt.net>]

For sharded v2 repositories with few-enough messages, it is
possible for shard[0] to go unused and never trigger the
->commit_txn_lazy to set the indexlevel field in Xapian
metadata.

So set it immediately at initialization and avoid this case.
While we're at it, avoid triggering needless pwrite syscalls
from ->set_metadata by checking with ->get_metadata, first.
---
 lib/PublicInbox/SearchIdx.pm      | 26 +++++++++++++++++---------
 lib/PublicInbox/SearchIdxShard.pm |  4 +++-
 t/init.t                          |  7 ++++++-
 3 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/lib/PublicInbox/SearchIdx.pm b/lib/PublicInbox/SearchIdx.pm
index 44b05813..7d089e7a 100644
--- a/lib/PublicInbox/SearchIdx.pm
+++ b/lib/PublicInbox/SearchIdx.pm
@@ -58,6 +58,7 @@ sub new {
 		ibx_ver => $version,
 		indexlevel => $indexlevel,
 	}, $class;
+	$self->{-set_indexlevel_once} = 1 if $indexlevel eq 'medium';
 	$ibx->umask_prepare;
 	if ($version == 1) {
 		$self->{lock_path} = "$inboxdir/ssoma.lock";
@@ -842,20 +843,27 @@ sub begin_txn_lazy {
 	});
 }
 
+# store 'indexlevel=medium' in v2 shard=0 and v1 (only one shard)
+# This metadata is read by Admin::detect_indexlevel:
+sub set_indexlevel {
+	my ($self) = @_;
+
+	if (!$self->{shard} && # undef or 0, not >0
+			delete($self->{-set_indexlevel_once})) {
+		my $xdb = $self->{xdb};
+		my $level = $xdb->get_metadata('indexlevel');
+		if (!$level || $level ne 'medium') {
+			$xdb->set_metadata('indexlevel', 'medium');
+		}
+	}
+}
+
 sub commit_txn_lazy {
 	my ($self) = @_;
 	delete $self->{txn} or return;
 	$self->{-inbox}->with_umask(sub {
 		if (my $xdb = $self->{xdb}) {
-
-			# store 'indexlevel=medium' in v2 shard=0 and
-			# v1 (only one shard)
-			# This metadata is read by Admin::detect_indexlevel:
-			if (!$self->{shard} # undef or 0, not >0
-			    && $self->{indexlevel} eq 'medium') {
-				$xdb->set_metadata('indexlevel', 'medium');
-			}
-
+			set_indexlevel($self);
 			$xdb->commit_transaction;
 		}
 		$self->{over}->commit_lazy if $self->{over};
diff --git a/lib/PublicInbox/SearchIdxShard.pm b/lib/PublicInbox/SearchIdxShard.pm
index 2b48b1b4..1ea01095 100644
--- a/lib/PublicInbox/SearchIdxShard.pm
+++ b/lib/PublicInbox/SearchIdxShard.pm
@@ -11,9 +11,11 @@ use IO::Handle (); # autoflush
 
 sub new {
 	my ($class, $v2writable, $shard) = @_;
-	my $self = $class->SUPER::new($v2writable->{-inbox}, 1, $shard);
+	my $ibx = $v2writable->{-inbox};
+	my $self = $class->SUPER::new($ibx, 1, $shard);
 	# create the DB before forking:
 	$self->_xdb_acquire;
+	$self->set_indexlevel;
 	$self->_xdb_release;
 	$self->spawn_worker($v2writable, $shard) if $v2writable->{parallel};
 	$self;
diff --git a/t/init.t b/t/init.t
index e20ff006..a78c2fc8 100644
--- a/t/init.t
+++ b/t/init.t
@@ -5,6 +5,7 @@ use warnings;
 use Test::More;
 use PublicInbox::Config;
 use PublicInbox::TestCommon;
+use PublicInbox::Admin;
 use File::Basename;
 my ($tmpdir, $for_destroy) = tmpdir();
 sub quiet_fail {
@@ -72,11 +73,15 @@ SKIP: {
 	quiet_fail($cmd, 'initializing V2 as V1 fails');
 
 	foreach my $lvl (qw(medium basic)) {
+		my $dir = "$tmpdir/v2$lvl";
 		$cmd = [ '-init', "v2$lvl", '-V2', '-L', $lvl,
-			"$tmpdir/v2$lvl", "http://example.com/v2$lvl",
+			$dir, "http://example.com/v2$lvl",
 			"v2$lvl\@example.com" ];
 		ok(run_script($cmd), "-init -L $lvl");
 		is(read_indexlevel("v2$lvl"), $lvl, "indexlevel set to '$lvl'");
+		my $ibx = PublicInbox::Inbox->new({ inboxdir => $dir });
+		is(PublicInbox::Admin::detect_indexlevel($ibx), $lvl,
+			'detected expected level w/o config');
 	}
 
 	# loop for idempotency