DB::Batch - Run database queries in batches through DBI
DB::Batch is a system for breaking up queries into batches behind the scenes, while maintaining the appearance of running a single query. Queries are run against an instance of DBI. For example, a query like: SELECT * FROM TABLE is expressed as: SELECT * FROM TABLE WHERE id BETWEEN # AND # and would be executed as: SELECT * FROM TABLE WHERE id BETWEEN 1 AND 100 SELECT * FROM TABLE WHERE id BETWEEN 101 AND 200 SELECT * FROM TABLE WHERE id BETWEEN 201 AND 300 ... Until the MAX(id) is reached. The script running this query, however, acts as if you are just running 'SELECT * FROM TABLE'. The purpose of this is to diminish load on a sql database when large amounts of data need to be retrieved by managing batch size and throttling.
In this example, we use a BETWEEN clause with two '#' placeholders. During execution the values in these placeholders are automatically incremented in chunks of 1000 (based on the batch size sent in) The execution starts at the given start and end values, which can be defined as integers or sql statements
calling $batch->fetchrow_array, fetchrow_hashref, or fetchrow_array will return all rows from the table, however in the background it will be running separate queries for each batch
use DB::Batch; use DBI; my $dbh = DBI->connect(...); my $batch = DB::Batch->new(dbh => $dbh); my $sql = 'SELECT id,col FROM table WHERE id BETWEEN # AND #'; my %db_args = ( start => 1, end => 'SELECT MAX(id) FROM table', batch => 1000, sleep => 1, ); # this will retrieve all rows from table while (my ($id,$col) = $batch->fetchrow_array($sql,\%db_args) { print "$id,$col \n"; }
In this example, DB::Batch will automatically increment our values for LIMIT and OFFSET behind the scenes until 1000 rows have been returned. (Note: this method is not optimal for very large data sets)
use DB::Batch; use DBI; my $dbh = DBI->connect(...); my $batch = DB::Batch->new(dbh => $dbh); my $sql = 'SELECT id,col FROM table WHERE id LIMIT # OFFSET #'; # you can also use the form: # my $sql = 'SELECT id,col FROM table WHERE id LIMIT #,#'; my %db_args = ( start => 1, limit => 1000, batch => 100, sleep => 1, ); # this will retrieve all rows from table while (my ($id,$col) = $batch->fetchrow_array($sql,\%db_args) { print "$id,$col \n"; }
In this example we provide a list of arguments and tell DB::Batch to bind 10 values at a time. The '#' will be expanded to the number of placeholders specified by makebinds, or up to as many placeholders that are needed to bind all the values of the given list.
use DB::Batch; use DBI; my $dbh = DBI->connect(...); my $batch = DB::Batch->new(dbh => $dbh); my $sql = 'SELECT id,col FROM table WHERE id IN (#)'; my %db_args = ( list => [qw(1..105)], makebinds => 10, ); # this will retrieve all rows from table while (my ($id,$col) = $batch->fetchrow_array($sql,\%db_args) { print "$id,$col \n"; }
Inserting can be done in batches using do_batch. In this example, 10 values from the given list will be binded and executed at a time behind the scenes.
use DB::Batch; use DBI; my $dbh = DBI->connect(...); my $batch = DB::Batch->new(dbh => $dbh); my $sql = "UPDATE foo SET col='abc' WHERE id IN (#)"; my %db_args = ( list => [qw(1..105)], makebinds => 10, ); # this will retrieve all rows from table $batch->do_batch($sql,\%db_args);
inserting multiple rows at once can be done by specifying the number of groups and number of placeholders with makebinds
use DB::Batch; use DBI; my $dbh = DBI->connect(...); my $batch = DB::Batch->new(dbh => $dbh); my $sql = 'INSERT INTO foo (col1,col2) VALUES #'; my %db_args = ( list => [qw(1 col2value2 2 col2value2 3 col2value3)], makebinds => 2, # groups => 3, # make 3 groups of 2 placeholders ); # this will retrieve all rows from table $batch->do_batch($sql,\%db_args);
If the flow of control of your script requires you to iterate over a large amount of data, use buffer_batch to buffer a number of rows of data and then execute it all at once in the end
use DB::Batch; use DBI; my $dbh = DBI->connect(...); my $batch = DB::Batch->new(dbh => $dbh); my $sql = 'INSERT INTO foo (col1,col2) VALUES #'; my @data = (1..10000); my %db_args = ( makebinds => 2, # groups => 3, # make 3 groups of 2 placeholders ); for my $col1 (@data) { my $col2 = $col1; $batch->buffer_batch($sql,$col1,$col2); } $batch->exec_buffer($sql,\%db_args);
Hooks
use DB::Batch; use DBI; my $dbh = DBI->connect(...); my $batch = DB::Batch->new(dbh => $dbh); my $sql = 'SELECT id,col FROM table WHERE id BETWEEN # AND #'; my $insert = 'INSERT INTO foo (col1,col2) VALUES #'; my %db_args = ( start => 1, end => 'SELECT MAX(id) FROM table', batch => 1000, sleep => 1, pre_hook => sub { # this is executed before the query is run through $dbh->prepare print Dumper [ $batch->get_last_batch() ]; # returns values about to be bound }, post_hook => sub { # This will run the INSERT after each batch of the SELECT query is finished, # this way the entire table worth of data doesn't need to be kept in memory # and written all at once $batch->exec_buffer($insert,{makebinds => 2, groups => 10}); } ); # this will retrieve all rows from table while (my ($id,$col) = $batch->fetchrow_array($sql,\%db_args) { # returns true if a new batch was started behind the scenes if ($batch->is_new_batch()) { print Dumper [ $batch->get_last_batch() ]; # returns current values being bound } # you can buffer results from one query to insert in batches to another table $batch->buffer_batch($insert,$id,$col); }
-- start at id 0, and run the query in increments of 100 up to 1000. SQL_STRING: 'SELECT foo FROM table WHERE id BETWEEN # AND #' ARGS: { start => 0 end => 1000, batch => 100 sleep => 100000 # number of microseconds to wait between queries pre_hook => sub { # do something prior to current sth being prepared }, post_hook => sub { # do something after current sth is finished } } -- determine start and end values at runtime based on the results of the given queries ARGS: { start => 'SELECT MIN(id) FROM table' end => 'SELECT MAX(id) FROM table', batch => 100 } -- expand the placeholder into 10 placeholders and bind the values of 'list' 10 at a time SQL_STRING: 'SELECT foo FROM table WHERE id IN (#)' ARGS: { makebinds => 10, list => [qw(2 4 6 8 10 12 14 16 18 20)], }
buffer the values in @LIST to be bound and run when exec_buffer is called on the same SQL_STRING
run do_batch after having buffered a list of bind values using buffer_batch(); -- args are identical to do_batch, except 'list' was build internally when buffer_batch was called SQL_STRING: 'INSERT INTO table VALUES #' ARGS: { makebinds => 10, }
buffer the values in @LIST to be bound and run when exec_buffer is called on the same SQL_STRING when the number of rows of data matches $ARGS->{trigger}, the insert is executed automatically
execute write queries in batches SQL_STRING: 'INSERT INTO table VALUES #' ARGS: { makebinds => 3, groups => 2 }
return the primary db handle being used
return a list of the last batch values bound to the current query
return a string with the full query that was last executed.
call this from inside a while($batch->fetch...) { } loop. Return the statement handle currently being processed
call this from inside a while($batch->fetch...) { } loop. Returns 1 if a new query batch was executed.
Copyright 2010, Chris Becker <clbecker@gmail.com>
<clbecker@gmail.com>
Original work sponsered by Shutterstock, LLC. http://shutterstock.com
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
To install DB::Batch, copy and paste the appropriate command in to your terminal.
cpanm
cpanm DB::Batch
CPAN shell
perl -MCPAN -e shell install DB::Batch
For more information on module installation, please visit the detailed CPAN module installation guide.