- $sth = $dbh->prepare('SELECT oidbin,uid FROM blob2num WHERE fid = ?');
- $sth->execute($fid);
- while (my ($oidbin, $id) = $sth->fetchrow_array) {
- $cb->($oidbin, $id, @args);
+
+ # minimize implicit txn time to avoid blocking writers by
+ # batching SELECTs. This looks wonky but is necessary since
+ # $cb-> may access the DB on its own.
+ my $ary = $dbh->selectall_arrayref(<<'', undef, $fid);
+SELECT _rowid_,oidbin,uid FROM blob2num WHERE fid = ?
+ORDER BY _rowid_ ASC LIMIT 1000
+
+ my $min = @$ary ? $ary->[-1]->[0] : undef;
+ while (defined $min) {
+ for my $row (@$ary) { $cb->($row->[1], $row->[2], @args) }
+
+ $ary = $dbh->selectall_arrayref(<<'', undef, $fid, $min);
+SELECT _rowid_,oidbin,uid FROM blob2num WHERE fid = ? AND _rowid_ > ?
+ORDER BY _rowid_ ASC LIMIT 1000
+
+ $min = @$ary ? $ary->[-1]->[0] : undef;