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DBD-Recall-1.10
River stage zero No dependents
++
/ DBD::Recall

NAME

DBD::Recall - Database fault tolerance through replication.

VERSION

 $Revision: 1.10 $
 $Date: 2001/05/27 10:52:16 $

SYNOPSIS

  use DBI;

  my $replicas = '192.168.1.1:7000,192.168.1.2:7000,192.168.1.3:7000';
  my $dsn = "DBI:Recall:database=$replicas";

  my $drh = DBI->install_driver ($driver, { Replicas => $replicas }); 
  my @dbs = $drh->func( "_ListDBs" ); 
  print (join "\n",@dbs,"\n");

  my $dbh = DBI->connect($dsn);
  my @tables = $dbh->tables();
  print (join "\n",@tables,"\n");

DESCRIPTION

This module interfaces to Recall, a data replication library written by Eric Newton, to provide transparent fault tolerance for database applications.

Recall is based on a data replication algorithm developed at DEC's SRC for the Echo filesystem. It implements a fast protocol with low network overhead and guranteed fault tolerance as long as n of 2n-1 replica nodes are up.

The DBD::Recall interface allows you to add fault tolerance to your database applications by a trivial change in your code. Simply use this module instead of the DBD you are currently using.

To achieve replicated functionality you'll also need to set up a few pieces of external infrastucture, such as the replica servers, and rsync access between replicas. This is all described in greater detail in Replication::Recall::DBServer.

WARNING

DBD::Recall is a hack that attempts to accomplish something (fault-tolerance through replication) at the perl DBD driver level that would be better implemented by database servers. It works, but it is not pretty.

Some commercial servers, such as Oracle, do implement replication. If speed and reliability are critical to your application, you will probably be better off with one of the commercial databases that implement replication within the database engine.

I've only tried DBD::Recall with MySQL so far on Debian GNU/Linux. If you get it to work with another database engine or on another operating system, please email me about your experiences so I can include information about your platform in future releases.

BUGS

  • Transparency is accomplished through a remote delegation hack which might break under certain circumstances. If this happens to you, please let me know.

  • There must be loads more. Let me know if you find some.

AUTHOR

DBD::Recall is Copyright (c) 2000 Ashish Gulhati <hash@netropolis.org>. All Rights Reserved.

ACKNOWLEDGEMENTS

Thanks to Barkha for inspiration, laughs and all 'round good times; and to Eric Newton, Gurusamy Sarathy, Larry Wall, Richard Stallman and Linus Torvalds for all the great software.

LICENSE

This code is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

DISCLAIMER

This is free software. If it breaks, you own both parts.