Remove --chunk-index-columns and extend --chunk-index instead to take INDEX:N value. Add n_index_values to TableNibbler.

lib/NibbleIterator.pm

@@ -124,10 +124,11 @@ sub new {
       # Figure out how to nibble the table with the index.
       my $asc = $args{TableNibbler}->generate_asc_stmt(
          %args,
-         tbl_struct => $tbl->{tbl_struct},
-         index      => $index,
-         cols       => \@cols,
-         asc_only   => 1,
+         tbl_struct   => $tbl->{tbl_struct},
+         index        => $index,
+         n_index_cols => $args{n_chunk_index_cols},
+         cols         => \@cols,
+         asc_only     => 1,
       );
       PTDEBUG && _d('Ascend params:', Dumper($asc));
 

lib/TableNibbler.pm

@@ -41,6 +41,7 @@ sub new {
 # * tbl_struct    Hashref returned from TableParser::parse().
 # * cols          Arrayref of columns to SELECT from the table
 # * index         Which index to ascend; optional.
+# * n_index_cols  The number of left-most index columns to use.
 # * asc_only      Whether to ascend strictly, that is, the WHERE clause for
 #                 the asc_stmt will fetch the next row > the given arguments.
 #                 The option is to fetch the row >=, which could loop
@@ -77,8 +78,12 @@ sub generate_asc_stmt {
    # These are the columns we'll ascend.
    my @asc_cols = @{$tbl_struct->{keys}->{$index}->{cols}};
    if ( $args{asc_first} ) {
-      @asc_cols = $asc_cols[0];
       PTDEBUG && _d('Ascending only first column');
+      @asc_cols = $asc_cols[0];
+   }
+   elsif ( my $n = $args{n_index_cols} ) {
+      PTDEBUG && _d('Ascending only first', $n, 'columns');
+      @asc_cols = @asc_cols[0..($n-1)];
    }
    PTDEBUG && _d('Will ascend columns', join(', ', @asc_cols));