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

bin/pt-table-checksum

@@ -5991,6 +5991,25 @@ sub main {
       }
    }
 
+   # Parse --chunk-index INDEX:N where N is the number of
+   # left-most columns of INDEX to use.
+   # https://bugs.launchpad.net/percona-toolkit/+bug/1010232
+   my ($chunk_index, $n_chunk_index_cols)
+      = split(':', $o->get('chunk-index') || '');
+   if ( defined $chunk_index && !$chunk_index ) {
+      $o->save_error('--chunk-index cannot be an empty string');
+   }
+   else {
+      $chunk_index = lc $chunk_index;
+   }
+   if ( defined $n_chunk_index_cols
+        && (!$n_chunk_index_cols
+            || $n_chunk_index_cols =~ m/[^\d]/
+            || $n_chunk_index_cols < 1) ) {
+      $o->save_error('Invalid number of --chunk-index columns: '
+         . $n_chunk_index_cols);
+   }
+
    if ( !$o->get('help') ) {
       if ( @ARGV > 1 ) {
          $o->save_error("More than one host specified; only one allowed");
@@ -6910,22 +6929,23 @@ sub main {
          my $nibble_iter;
          eval {
             $nibble_iter = new OobNibbleIterator(
-               Cxn          => $master_cxn,
-               tbl          => $tbl,
-               chunk_size   => $tbl->{chunk_size},
-               chunk_index  => $o->get('chunk-index'),
-               dml          => $checksum_dml,
-               select       => $checksum_cols,
-               past_dml     => $checksum_dml,
-               past_select  => $past_cols,
-               callbacks    => $callbacks,
-               resume       => $last_chunk,
-               OptionParser => $o,
-               Quoter       => $q,
-               TableNibbler => $tn,
-               TableParser  => $tp,
-               RowChecksum  => $rc,
-               comments     => {
+               Cxn                => $master_cxn,
+               tbl                => $tbl,
+               chunk_size         => $tbl->{chunk_size},
+               chunk_index        => $chunk_index,
+               n_chunk_index_cols => $n_chunk_index_cols,
+               dml                => $checksum_dml,
+               select             => $checksum_cols,
+               past_dml           => $checksum_dml,
+               past_select        => $past_cols,
+               callbacks          => $callbacks,
+               resume             => $last_chunk,
+               OptionParser       => $o,
+               Quoter             => $q,
+               TableNibbler       => $tn,
+               TableParser        => $tp,
+               RowChecksum        => $rc,
+               comments           => {
                   bite   => "checksum table",
                   nibble => "checksum chunk",
                },
@@ -8037,12 +8057,6 @@ when using this option; a poor choice of index could cause bad performance.
 This is probably best to use when you are checksumming only a single table, not
 an entire server.
 
-=item --chunk-index-columns
-
-type: int
-
-Number of left-most L<"--chunk-index"> columns to use.
-
 =item --chunk-size
 
 type: size; default: 1000

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));
 

t/lib/TableNibbler.t

@@ -9,7 +9,7 @@ BEGIN {
 use strict;
 use warnings FATAL => 'all';
 use English qw(-no_match_vars);
-use Test::More tests => 24;
+use Test::More tests => 25;
 
 use TableParser;
 use TableNibbler;
@@ -297,6 +297,34 @@ is_deeply(
    'Alternate index with asc_first on sakila.rental',
 );
 
+is_deeply(
+   $n->generate_asc_stmt(
+      tbl_struct   => $t,
+      cols         => $t->{cols},
+      index        => 'rental_date',
+      n_index_cols => 2,
+   ),
+   {
+      cols  => [qw(rental_id rental_date inventory_id customer_id
+                  return_date staff_id last_update)],
+      index => 'rental_date',
+      where => '((`rental_date` > ?) OR (`rental_date` = ? AND `inventory_id` >= ?))',
+      slice => [qw(1 1 2)],
+      scols => [qw(rental_date rental_date inventory_id)],
+      boundaries => {
+         '<'  =>
+         '((`rental_date` < ?) OR (`rental_date` = ? AND `inventory_id` < ?))',
+         '<=' =>
+         '((`rental_date` < ?) OR (`rental_date` = ? AND `inventory_id` <= ?))',
+         '>'  =>
+         '((`rental_date` > ?) OR (`rental_date` = ? AND `inventory_id` > ?))',
+         '>=' =>
+         '((`rental_date` > ?) OR (`rental_date` = ? AND `inventory_id` >= ?))'
+      },
+   },
+   'Use only N left-most columns of the index',
+);
+
 is_deeply(
    $n->generate_asc_stmt(
       tbl_struct => $t,