diff --git a/bin/pt-online-schema-change b/bin/pt-online-schema-change
index 31f09bd5..a1d968c1 100755
--- a/bin/pt-online-schema-change
+++ b/bin/pt-online-schema-change
@@ -5457,6 +5457,7 @@ use strict;
 use warnings FATAL => 'all';
 use English qw(-no_match_vars);
 use constant PTDEBUG => $ENV{PTDEBUG} || 0;
+use IndexLength;
 
 use Data::Dumper;
 $Data::Dumper::Indent    = 1;
@@ -5497,9 +5498,7 @@ sub new {
       my $nibble_sql
          = ($args{dml} ? "$args{dml} " : "SELECT ")
          . ($args{select} ? $args{select}
-         #                 : join(', ', map { $q->quote($_) } @cols))
-                           : join(', ', map{ $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' ?
-                                   "CAST(".$q->quote($_)." AS UNSIGNED)" : $q->quote($_) } @cols))
+                          : join(', ', map { $q->quote($_) } @cols))
          . " FROM $tbl->{name}"
          . ($where ? " WHERE $where" : '')
          . ($args{lock_in_share_mode} ? " LOCK IN SHARE MODE" : "")
@@ -5509,9 +5508,7 @@ sub new {
       my $explain_nibble_sql
          = "EXPLAIN SELECT "
          . ($args{select} ? $args{select}
-         #                 : join(', ', map { $q->quote($_) } @cols))
-                           : join(', ', map{ $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' ?
-                                   "CAST(".$q->quote($_)." AS UNSIGNED)" : $q->quote($_) } @cols))
+                          : join(', ', map { $q->quote($_) } @cols))
          . " FROM $tbl->{name}"
          . ($where ? " WHERE $where" : '')
          . ($args{lock_in_share_mode} ? " LOCK IN SHARE MODE" : "")
@@ -5540,43 +5537,40 @@ sub new {
       );
       PTDEBUG && _d('Ascend params:', Dumper($asc));
 
-      #      my $force_concat_enums = $o->has('force-concat-enums') && $o->get('force-concat-enums');
-      #      my $i=0;
-      #      for my $index (@{$index_cols}) {
-      #          last if $args{n_chunk_index_cols} && $i >= $args{n_chunk_index_cols};
-      #          $i++;
-      #          if ($tbl->{tbl_struct}->{type_for}->{$index} eq 'enum') {
-      #             if ($tbl->{tbl_struct}->{defs}->{$index} =~ m/enum\s*\((.*?)\)/) {
-      #                 my @items = split(/,\s*/, $1);
-      #                 my $sorted = 1; # Asume the items list is sorted to later check if this is true
-      #                 for (my $i=1; $i < scalar(@items); $i++) {
-      #                     if ($items[$i-1] gt $items[$i]) {
-      #                         $sorted = 0;
-      #                         last;
-      #                     }
-      #                 }
-      #                 if (!$force_concat_enums && !$sorted) {
-      #                    die "The index " . $index . " in table " .  $tbl->{name} .
-      #                    " has unsorted enum items.\nPlease read the documentation for the --force-concat-enums parameter\n";
-      #                 }
-      #             }
-      #          }
-      #      }
+      my $force_concat_enums = $o->has('force-concat-enums') && $o->get('force-concat-enums');
+      my $i=0;
+      for my $index (@{$index_cols}) {
+          last if $args{n_chunk_index_cols} && $i >= $args{n_chunk_index_cols};
+          $i++;
+          if ($tbl->{tbl_struct}->{type_for}->{$index} eq 'enum') {
+             if ($tbl->{tbl_struct}->{defs}->{$index} =~ m/enum\s*\((.*?)\)/) {
+                 my @items = split(/,\s*/, $1);
+                 my $sorted = 1; # Asume the items list is sorted to later check if this is true
+                 for (my $i=1; $i < scalar(@items); $i++) {
+                     if ($items[$i-1] gt $items[$i]) {
+                         $sorted = 0;
+                         last;
+                     }
+                 }
+                 if (!$force_concat_enums && !$sorted) {
+                    die "The index " . $index . " in table " .  $tbl->{name} .
+                    " has unsorted enum items.\nPlease read the documentation for the --force-concat-enums parameter\n";
+                 }
+             }
+          }
+      }
 
 
       my $from     = "$tbl->{name} FORCE INDEX(`$index`)";
-      #my $order_by = join(', ', map { $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' && $force_concat_enums
-      #                                  ? "CONCAT(".$q->quote($_).")" : $q->quote($_)} @{$index_cols});
-      my $order_by = join(', ', map {$q->quote($_)} @{$index_cols});
+      my $order_by = join(', ', map { $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' && $force_concat_enums
+                                        ? "CONCAT(".$q->quote($_).")" : $q->quote($_)} @{$index_cols});
 
-      #my $order_by_dec = join(' DESC,', map { $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' && $force_concat_enums
-      #                                  ? "CONCAT(".$q->quote($_).")" : $q->quote($_)} @{$index_cols});
-      my $order_by_dec = join(' DESC,', map {$q->quote($_)} @{$index_cols});
+      my $order_by_dec = join(' DESC,', map { $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' && $force_concat_enums
+                                        ? "CONCAT(".$q->quote($_).")" : $q->quote($_)} @{$index_cols});
 
       my $first_lb_sql
          = "SELECT /*!40001 SQL_NO_CACHE */ "
-         #. join(', ', map { $q->quote($_) } @{$asc->{scols}})
-         . join(', ', map { $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' ? "CAST(".$q->quote($_)." AS UNSIGNED)" : $q->quote($_)} @{$asc->{scols}})
+         . join(', ', map { $q->quote($_) } @{$asc->{scols}})
          . " FROM $from"
          . ($where ? " WHERE $where" : '')
          . " ORDER BY $order_by"
@@ -5588,8 +5582,7 @@ sub new {
       if ( $args{resume} ) {
          $resume_lb_sql
             = "SELECT /*!40001 SQL_NO_CACHE */ "
-            #. join(', ', map { $q->quote($_) } @{$asc->{scols}})
-            . join(', ', map { $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' ? "CAST(".$q->quote($_)." AS UNSIGNED)" : $q->quote($_)} @{$asc->{scols}})
+            . join(', ', map { $q->quote($_) } @{$asc->{scols}})
             . " FROM $from"
             . " WHERE " . $asc->{boundaries}->{'>'}
             . ($where ? " AND ($where)" : '')
@@ -5601,8 +5594,7 @@ sub new {
 
       my $last_ub_sql
          = "SELECT /*!40001 SQL_NO_CACHE */ "
-         #. join(', ', map { $q->quote($_) } @{$asc->{scols}})
-         . join(', ', map { $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' ? "CAST(".$q->quote($_)." AS UNSIGNED)" : $q->quote($_)} @{$asc->{scols}})
+         . join(', ', map { $q->quote($_) } @{$asc->{scols}})
          . " FROM $from"
          . ($where ? " WHERE $where" : '')
          . " ORDER BY "
@@ -5613,8 +5605,7 @@ sub new {
 
       my $ub_sql
          = "SELECT /*!40001 SQL_NO_CACHE */ "
-         #. join(', ', map { $q->quote($_) } @{$asc->{scols}})
-         . join(', ', map { $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' ? "CAST(".$q->quote($_)." AS UNSIGNED)" : $q->quote($_)} @{$asc->{scols}})
+         . join(', ', map { $q->quote($_) } @{$asc->{scols}})
          . " FROM $from"
          . " WHERE " . $asc->{boundaries}->{'>='}
                      . ($where ? " AND ($where)" : '')
@@ -5626,8 +5617,7 @@ sub new {
       my $nibble_sql
          = ($args{dml} ? "$args{dml} " : "SELECT ")
          . ($args{select} ? $args{select}
-         #                          : join(', ', map { $q->quote($_) } @{$asc->{cols}}))
-                                    : join(', ', map { $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' ? "CAST(".$q->quote($_)." AS UNSIGNED)" : $q->quote($_)} @{$asc->{cols}}))
+                          : join(', ', map { $q->quote($_) } @{$asc->{cols}}))
          . " FROM $from"
          . " WHERE " . $asc->{boundaries}->{'>='}  # lower boundary
          . " AND "   . $asc->{boundaries}->{'<='}  # upper boundary
@@ -5741,7 +5731,7 @@ sub next {
       if ( !$self->{have_rows} ) {
          $self->{nibbleno}++;
          PTDEBUG && _d('Nibble:', $self->{nibble_sth}->{Statement}, 'params:',
-            join(', ', (@{$self->{lower}} || [], @{$self->{upper} }||[])));
+            join(', ', (@{$self->{lower} || []}, @{$self->{upper} || []})));
          if ( my $callback = $self->{callbacks}->{exec_nibble} ) {
             $self->{have_rows} = $callback->(%callback_args);
          }
@@ -5832,8 +5822,12 @@ sub set_boundary {
 }
 
 sub one_nibble {
-   my ($self) = @_;
-   return $self->{one_nibble};
+   my ($self, $value) = @_;
+   if (@_ == 2) {
+       $self->{one_nibble} = $value;
+   } else {
+       return $self->{one_nibble};
+   }
 }
 
 sub limit {
@@ -5867,11 +5861,11 @@ sub row_estimate {
 
 sub can_nibble {
    my (%args) = @_;
-   my @required_args = qw(Cxn tbl chunk_size OptionParser TableParser);
+   my @required_args = qw(Cxn tbl chunk_size OptionParser TableParser Quoter);
    foreach my $arg ( @required_args ) {
       die "I need a $arg argument" unless $args{$arg};
    }
-   my ($cxn, $tbl, $chunk_size, $o) = @args{@required_args};
+   my ($cxn, $tbl, $chunk_size, $o, $q) = @args{@required_args};
 
    my $where = $o->has('where') ? $o->get('where') : '';
 
@@ -5881,6 +5875,23 @@ sub can_nibble {
       where => $where,
    );
 
+   my $can_get_keys;
+   if ($mysql_index) {
+       my $idx_len = IndexLength->new(Quoter => $q);
+       my ($key_len, $key) = $idx_len->index_length(
+           Cxn          => $args{Cxn},
+           tbl          => $tbl,
+           index        => $mysql_index,
+           n_index_cols => $o->get('chunk-index-columns'),
+       );
+
+       if ( !$key || !$key_len || lc($key) ne lc($mysql_index)) {
+           $can_get_keys = 0;
+       } else {
+           $can_get_keys = 1;
+       }
+   } 
+
    if ( !$where ) {
       $mysql_index = undef;
    }
@@ -5889,6 +5900,10 @@ sub can_nibble {
    my $one_nibble = !defined $args{one_nibble} || $args{one_nibble}
                   ? $row_est <= $chunk_size * $chunk_size_limit
                   : 0;
+   if (!$can_get_keys) {
+       $one_nibble = 1;
+   }
+
    PTDEBUG && _d('One nibble:', $one_nibble ? 'yes' : 'no');
 
    if ( $args{resume}
@@ -6140,7 +6155,7 @@ sub _next_boundaries {
 
 
    PTDEBUG && _d($self->{ub_sth}->{Statement}, 'params:',
-      join(', ', @{$self->{lower}} || []), $self->{limit});
+      join(', ', @{$self->{lower}}), $self->{limit});
    $self->{ub_sth}->execute(@{$self->{lower}}, $self->{limit});
    my $boundary = $self->{ub_sth}->fetchall_arrayref();
    PTDEBUG && _d('Next boundary:', Dumper($boundary));
@@ -6181,9 +6196,6 @@ sub identical_boundaries {
       if scalar @$b1 != scalar @$b2;  # shouldn't happen
    my $n_vals = scalar @$b1;
    for my $i ( 0..($n_vals-1) ) {
-      next if (!defined($b1->[$i]) && !defined($b2->[$i]));
-      return 0 if (!defined($b1->[$i]) && defined($b2->[$i])); # diff
-      return 0 if (defined($b1->[$i]) && !defined($b2->[$i])); # diff
       return 0 if $b1->[$i] ne $b2->[$i]; # diff
    }
    return 1;
@@ -9579,6 +9591,7 @@ sub main {
          # a single chunk on all slaves.  E.g. if a slave is out of sync
          # and has a lot more rows than the master, single chunking on the
          # master could cause the slave to choke.
+         my $failed_to_nibble;
          if ( $nibble_iter->one_nibble() ) {
             PTDEBUG && _d('Getting table row estimate on replicas');
             my @too_large;
@@ -9605,10 +9618,13 @@ sub main {
                      . ($tbl->{chunk_size} * $limit)
                      . " rows (chunk size=$tbl->{chunk_size}"
                      . " * chunk size limit=$limit).\n";
-               die ts($msg);
+               warn $msg;
+               $failed_to_nibble = 1;
+               $nibble_iter->one_nibble(0); # disable nibbling for this table
+               # die ts($msg);
             }
          }
-         else { # chunking the table
+         if (!$nibble_iter->one_nibble() || $failed_to_nibble) { # chunking the table
             if ( $o->get('check-plan') ) {
                my $idx_len = new IndexLength(Quoter => $q);
                my ($key_len, $key) = $idx_len->index_length(
diff --git a/bin/pt-table-checksum b/bin/pt-table-checksum
index 8ccabf4d..cc15207b 100755
--- a/bin/pt-table-checksum
+++ b/bin/pt-table-checksum
@@ -6593,6 +6593,7 @@ sub next {
       }
       $self->{rowno}     = 0;
       $self->{have_rows} = 0;
+      
    }
 
    PTDEBUG && _d('Done nibbling');
@@ -6657,8 +6658,12 @@ sub set_boundary {
 }
 
 sub one_nibble {
-   my ($self) = @_;
-   return $self->{one_nibble};
+   my ($self, $value) = @_;
+   if (@_ == 2) {
+       $self->{one_nibble} = $value;
+   } else {
+       return $self->{one_nibble};
+   }
 }
 
 sub limit {
@@ -6706,15 +6711,7 @@ sub can_nibble {
       where => $where,
    );
 
-   if ( !$where ) {
-       $mysql_index = undef;
-   } 
-
-   my $chunk_size_limit = $o->get('chunk-size-limit') || 1;
-   my $one_nibble = !defined $args{one_nibble} || $args{one_nibble}
-                  ? $row_est <= $chunk_size * $chunk_size_limit
-                  : 0;
-
+   my $can_get_keys;
    if ($mysql_index) {
        my $idx_len = IndexLength->new(Quoter => $q);
        my ($key_len, $key) = $idx_len->index_length(
@@ -6725,10 +6722,24 @@ sub can_nibble {
        );
 
        if ( !$key || !$key_len || lc($key) ne lc($mysql_index)) {
-           $one_nibble = 1;
+           $can_get_keys = 0;
+       } else {
+           $can_get_keys = 1;
        }
    } 
 
+   if ( !$where ) {
+      $mysql_index = undef;
+   }
+
+   my $chunk_size_limit = $o->get('chunk-size-limit') || 1;
+   my $one_nibble = !defined $args{one_nibble} || $args{one_nibble}
+                  ? $row_est <= $chunk_size * $chunk_size_limit
+                  : 0;
+   if (!$can_get_keys) {
+       $one_nibble = 1;
+   }
+
    PTDEBUG && _d('One nibble:', $one_nibble ? 'yes' : 'no');
 
    if ( $args{resume}
@@ -6906,7 +6917,7 @@ sub _get_bounds {
       if (    defined $nibble->{lower_boundary}
            && defined $nibble->{upper_boundary} ) {
          my $sth = $dbh->prepare($self->{resume_lb_sql});
-         my @ub = $self->{Quoter}->deserialize_list($nibble->{upper_boundary});
+         my @ub  = split ',', $nibble->{upper_boundary};
          PTDEBUG && _d($sth->{Statement}, 'params:', @ub);
          $sth->execute(@ub);
          $self->{next_lower} = $sth->fetchrow_arrayref();
diff --git a/lib/IndexLength.pm b/lib/IndexLength.pm
index c2f12055..d160a257 100644
--- a/lib/IndexLength.pm
+++ b/lib/IndexLength.pm
@@ -99,7 +99,7 @@ sub _get_first_values {
    }
    my ($cxn, $tbl, $index, $n_index_cols) = @args{@required_args};
 
-   my $q = $self->{quoter};
+   my $q = $self->{Quoter};
 
    # Select just the index columns.
    my $index_struct  = $tbl->{tbl_struct}->{keys}->{$index};
diff --git a/lib/NibbleIterator.pm b/lib/NibbleIterator.pm
index 50784af9..7fa31eed 100644
--- a/lib/NibbleIterator.pm
+++ b/lib/NibbleIterator.pm
@@ -121,6 +121,7 @@ sub new {
       };
    }
    else {
+      my $parms = _nibble_params($nibble_params, $tbl, %args, \@cols, $chunk_size, $where, \%comments, $q);
       my $index      = $nibble_params->{index}; # brevity
       my $index_cols = $tbl->{tbl_struct}->{keys}->{$index}->{cols};
 
@@ -293,9 +294,198 @@ sub new {
    $self->{pause_file} = $nibble_params->{pause_file};
    $self->{sleep}      = $args{sleep} || 60;
 
+   $self->{chunk_size} = $chunk_size;
+   $self->{comments}   = %comments;
+   $self->{cols}       = \@cols;
+   $self->{where}      = $where;
+   $self->{tbl}        = $tbl;
+
    return bless $self, $class;
 }
 
+sub _one_nibble {
+    my ($self, %args) = @_;
+    my $q        = new Quoter();
+    my $cols     = $self->{cols};
+    my $where    = $self->{where};
+    my $tbl      = $self->{tbl};
+    my %comments = $self->{comments};
+
+      # If the chunk size is >= number of rows in table, then we don't
+      # need to chunk; we can just select all rows, in order, at once.
+      my $nibble_sql
+         = ($args{dml} ? "$args{dml} " : "SELECT ")
+         . ($args{select} ? $args{select}
+                          : join(', ', map { $q->quote($_) } @$cols))
+         . " FROM $tbl->{name}"
+         . ($where ? " WHERE $where" : '')
+         . ($args{lock_in_share_mode} ? " LOCK IN SHARE MODE" : "")
+         . " /*$comments{bite}*/";
+      PTDEBUG && _d('One nibble statement:', $nibble_sql);
+
+      my $explain_nibble_sql
+         = "EXPLAIN SELECT "
+         . ($args{select} ? $args{select}
+                          : join(', ', map { $q->quote($_) } @$cols))
+         . " FROM $tbl->{name}"
+         . ($where ? " WHERE $where" : '')
+         . ($args{lock_in_share_mode} ? " LOCK IN SHARE MODE" : "")
+         . " /*explain $comments{bite}*/";
+      PTDEBUG && _d('Explain one nibble statement:', $explain_nibble_sql);
+
+      return {
+         one_nibble         => 1,
+         limit              => 0,
+         nibble_sql         => $nibble_sql,
+         explain_nibble_sql => $explain_nibble_sql,
+      };
+}
+
+sub _nibble_params {
+      my ($nibble_params, $tbl, %args, $cols, $chunk_size, $where, %comments, $q) = @_;
+      my $index      = $nibble_params->{index}; # brevity
+      my $index_cols = $tbl->{tbl_struct}->{keys}->{$index}->{cols};
+
+      # 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,
+         n_index_cols => $args{n_chunk_index_cols},
+         cols         => $cols,
+         asc_only     => 1,
+      );
+      PTDEBUG && _d('Ascend params:', Dumper($asc));
+
+      # Check if enum fields items are sorted or not.
+      # If they are sorted we can skip adding CONCAT to improve the queries eficiency.
+      my $force_concat_enums;
+
+      # Make SQL statements, prepared on first call to next().  FROM and
+      # ORDER BY are the same for all statements.  FORCE IDNEX and ORDER BY
+      # are needed to ensure deterministic nibbling.
+
+      my $from     = "$tbl->{name} FORCE INDEX(`$index`)";
+      my $order_by = join(', ', map { $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' && $force_concat_enums
+                                        ? "CONCAT(".$q->quote($_).")" : $q->quote($_)} @{$index_cols});
+
+      my $order_by_dec = join(' DESC,', map { $tbl->{tbl_struct}->{type_for}->{$_} eq 'enum' && $force_concat_enums
+                                        ? "CONCAT(".$q->quote($_).")" : $q->quote($_)} @{$index_cols});
+
+      # The real first row in the table.  Usually we start nibbling from
+      # this row.  Called once in _get_bounds().
+      my $first_lb_sql
+         = "SELECT /*!40001 SQL_NO_CACHE */ "
+         . join(', ', map { $q->quote($_) } @{$asc->{scols}})
+         . " FROM $from"
+         . ($where ? " WHERE $where" : '')
+         . " ORDER BY $order_by"
+         . " LIMIT 1"
+         . " /*first lower boundary*/";
+      PTDEBUG && _d('First lower boundary statement:', $first_lb_sql);
+
+      # If we're resuming, this fetches the effective first row, which
+      # should differ from the real first row.  Called once in _get_bounds().
+      my $resume_lb_sql;
+      if ( $args{resume} ) {
+         $resume_lb_sql
+            = "SELECT /*!40001 SQL_NO_CACHE */ "
+            . join(', ', map { $q->quote($_) } @{$asc->{scols}})
+            . " FROM $from"
+            . " WHERE " . $asc->{boundaries}->{'>'}
+            . ($where ? " AND ($where)" : '')
+            . " ORDER BY $order_by"
+            . " LIMIT 1"
+            . " /*resume lower boundary*/";
+         PTDEBUG && _d('Resume lower boundary statement:', $resume_lb_sql);
+      }
+
+      # The nibbles are inclusive, so we need to fetch the real last row
+      # in the table.  Saved as boundary last_upper and used as boundary
+      # upper in some cases.  Called once in _get_bounds().
+      my $last_ub_sql
+         = "SELECT /*!40001 SQL_NO_CACHE */ "
+         . join(', ', map { $q->quote($_) } @{$asc->{scols}})
+         . " FROM $from"
+         . ($where ? " WHERE $where" : '')
+         . " ORDER BY "
+         . $order_by_dec . ' DESC'
+         . " LIMIT 1"
+         . " /*last upper boundary*/";
+      PTDEBUG && _d('Last upper boundary statement:', $last_ub_sql);
+
+      # Nibbles are inclusive, so for a..z, the nibbles are: a-e, f-j, k-o, p-t,
+      # u-y, and z.  This complicates getting the next upper boundary because
+      # if we use either (col >= lb AND col < ub) or (col > lb AND col <= ub)
+      # in nibble_sql (below), then that fails for either the last or first
+      # nibble respectively.  E.g. (col >= z AND col < z) doesn't work, nor
+      # does (col > a AND col <= e).  Hence the fancy LIMIT 2 which returns
+      # the upper boundary for the current nibble *and* the lower boundary
+      # for the next nibble.  See _next_boundaries().
+      my $ub_sql
+         = "SELECT /*!40001 SQL_NO_CACHE */ "
+         . join(', ', map { $q->quote($_) } @{$asc->{scols}})
+         . " FROM $from"
+         . " WHERE " . $asc->{boundaries}->{'>='}
+                     . ($where ? " AND ($where)" : '')
+         . " ORDER BY $order_by"
+         . " LIMIT ?, 2"
+         . " /*next chunk boundary*/";
+      PTDEBUG && _d('Upper boundary statement:', $ub_sql);
+
+      # This statement does the actual nibbling work; its rows are returned
+      # to the caller via next().
+      my $nibble_sql
+         = ($args{dml} ? "$args{dml} " : "SELECT ")
+         . ($args{select} ? $args{select}
+                          : join(', ', map { $q->quote($_) } @{$asc->{cols}}))
+         . " FROM $from"
+         . " WHERE " . $asc->{boundaries}->{'>='}  # lower boundary
+         . " AND "   . $asc->{boundaries}->{'<='}  # upper boundary
+         . ($where ? " AND ($where)" : '')
+         . ($args{order_by} ? " ORDER BY $order_by" : "")
+         . ($args{lock_in_share_mode} ? " LOCK IN SHARE MODE" : "")
+         . " /*$comments{nibble}*/";
+      PTDEBUG && _d('Nibble statement:', $nibble_sql);
+
+      my $explain_nibble_sql 
+         = "EXPLAIN SELECT "
+         . ($args{select} ? $args{select}
+                          : join(', ', map { $q->quote($_) } @{$asc->{cols}}))
+         . " FROM $from"
+         . " WHERE " . $asc->{boundaries}->{'>='}  # lower boundary
+         . " AND "   . $asc->{boundaries}->{'<='}  # upper boundary
+         . ($where ? " AND ($where)" : '')
+         . ($args{order_by} ? " ORDER BY $order_by" : "")
+         . ($args{lock_in_share_mode} ? " LOCK IN SHARE MODE" : "")
+         . " /*explain $comments{nibble}*/";
+      PTDEBUG && _d('Explain nibble statement:', $explain_nibble_sql);
+
+      my $limit = $chunk_size - 1;
+      PTDEBUG && _d('Initial chunk size (LIMIT):', $limit);
+
+      my $params = {
+         index                => $index,
+         limit                => $limit,
+         first_lb_sql         => $first_lb_sql,
+         last_ub_sql          => $last_ub_sql,
+         ub_sql               => $ub_sql,
+         nibble_sql           => $nibble_sql,
+         explain_first_lb_sql => "EXPLAIN $first_lb_sql",
+         explain_ub_sql       => "EXPLAIN $ub_sql",
+         explain_nibble_sql   => $explain_nibble_sql,
+         resume_lb_sql        => $resume_lb_sql,
+         sql                  => {
+            columns    => $asc->{scols},
+            from       => $from,
+            where      => $where,
+            boundaries => $asc->{boundaries},
+            order_by   => $order_by,
+         },
+      };
+      return $params;
+}
+
 sub next {
    my ($self) = @_;
 
@@ -453,8 +643,12 @@ sub set_boundary {
 }
 
 sub one_nibble {
-   my ($self) = @_;
-   return $self->{one_nibble};
+   my ($self, $value) = @_;
+   if (@_ == 2) {
+       $self->{one_nibble} = $value;
+   } else {
+       return $self->{one_nibble};
+   }
 }
 
 sub limit {
diff --git a/t/lib/NibbleIterator.t b/t/lib/NibbleIterator.t
index 10f5548e..2431cadf 100644
--- a/t/lib/NibbleIterator.t
+++ b/t/lib/NibbleIterator.t
@@ -36,7 +36,6 @@ my $dp  = new DSNParser(opts=>$dsn_opts);
 my $sb  = new Sandbox(basedir => '/tmp', DSNParser => $dp);
 my $dbh = $sb->get_dbh_for('master');
 
-plan skip_all => 'Cannot connect to sandbox master';
 if ( !$dbh ) {
    plan skip_all => 'Cannot connect to sandbox master';
 } else {