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Implement dynamic chunk size, set_chunk_size().

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This commit is contained in:
Daniel Nichter
2011-09-12 07:32:19 -06:00
parent 0bb4497fbe
commit 3ed822e8e6
2 changed files with 102 additions and 18 deletions
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88
lib/NibbleIterator.pm
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@@ -91,17 +91,18 @@ sub new {
# 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 { $q->quote($_) } @{$index_cols})
. " FROM $from "
. " WHERE " . $asc->{boundaries}->{'>='} # lower boundary
. ($args{where} ? " AND ($args{where})" : '')
. " ORDER BY $order_by "
. " LIMIT 2 OFFSET " . (($o->get('chunk-size') || 1) - 1)
. " /*upper boundary*/";
MKDEBUG && _d('Next upper boundary statement:', $ub_sql);
my $ub_sql = _make_ub_sql(
cols => $index_cols,
from => $from,
where => $asc->{boundaries}->{'>='}
. ($args{where} ? " AND ($args{where})" : ''),
order_by => $order_by,
limit => $o->get('chunk-size'),
Quoter => $q,
);
# This statement does the actual nibbling work; its rows are returned
# to the caller via next().
my $nibble_sql
= ($args{dms} ? "$args{dms} " : "SELECT ")
. ($args{select} ? $args{select}
@@ -150,7 +151,11 @@ sub new {
my $self = {
%args,
asc => $asc,
index => $index,
index_cols => $index_cols,
from => $from,
order_by => $order_by,
first_lb_sql => $first_lb_sql,
last_ub_sql => $last_ub_sql,
ub_sql => $ub_sql,
@@ -181,8 +186,8 @@ sub next {
}
}
# If there's another boundary, fetch the rows within it.
BOUNDARY:
# If there's another nibble, fetch the rows within it.
NIBBLE:
while ( $self->{have_rows} || $self->_next_boundaries() ) {
# If no rows, then we just got the next boundaries, which start
# the next nibble.
@@ -249,6 +254,50 @@ sub nibble_number {
return $self->{nibbleno};
}
sub set_chunk_size {
my ($self, $limit) = @_;
MKDEBUG && _d('Setting new chunk size (LIMIT):', $limit);
$self->{ub_sql} = _make_ub_sql(
cols => $self->{index_cols},
from => $self->{from},
where => $self->{asc}->{boundaries}->{'>='}
. ($self->{where} ? " AND ($self->{where})" : ''),
order_by => $self->{order_by},
limit => $limit,
Quoter => $self->{Quoter},
);
# ub_sth won't exist if user calls this sub before calling next() once.
if ($self->{ub_sth}) {
$self->{ub_sth}->finish();
$self->{ub_sth} = undef;
}
$self->_prepare_sths();
return;
}
sub _make_ub_sql {
my (%args) = @_;
my @required_args = qw(cols from where order_by limit Quoter);
foreach my $arg ( @required_args ) {
die "I need a $arg argument" unless $args{$arg};
}
my ($cols, $from, $where, $order_by, $limit, $q) = @args{@required_args};
my $ub_sql
= "SELECT /*!40001 SQL_NO_CACHE */ "
. join(', ', map { $q->quote($_) } @{$cols})
. " FROM $from "
. " WHERE $where "
. " ORDER BY $order_by "
. " LIMIT 2 OFFSET " . ((int($limit) || 1) - 1)
. " /*upper boundary*/";
MKDEBUG && _d('Upper boundary statement:', $ub_sql);
return $ub_sql;
}
sub _can_nibble_once {
my ($self) = @_;
my ($dbh, $tbl, $q) = @{$self}{qw(dbh tbl Quoter)};
@@ -277,13 +326,18 @@ sub _prepare_sths {
my ($self) = @_;
MKDEBUG && _d('Preparing statement handles');
if ( $self->{one_nibble} ) {
$self->{nibble_sth} = $self->{dbh}->prepare($self->{one_nibble_sql});
$self->{explain_sth} = $self->{dbh}->prepare($self->{explain_one_nibble_sql});
$self->{nibble_sth} = $self->{dbh}->prepare($self->{one_nibble_sql})
unless $self->{nibble_sth};
$self->{explain_sth} = $self->{dbh}->prepare($self->{explain_one_nibble_sql})
unless $self->{explain_sth};
}
else {
$self->{ub_sth} = $self->{dbh}->prepare($self->{ub_sql});
$self->{nibble_sth} = $self->{dbh}->prepare($self->{nibble_sql});
$self->{explain_sth} = $self->{dbh}->prepare($self->{explain_nibble_sql});
$self->{ub_sth} = $self->{dbh}->prepare($self->{ub_sql})
unless $self->{ub_sth};
$self->{nibble_sth} = $self->{dbh}->prepare($self->{nibble_sql})
unless $self->{nibble_sth};
$self->{explain_sth} = $self->{dbh}->prepare($self->{explain_nibble_sql})
unless $self->{explain_sth};
}
}