KiokuDB::Backend::DBI - DBI backend for KiokuDB
my $dir = KiokuDB->connect( "dbi:mysql:foo", user => "blah", password => "moo', columns => [ # specify extra columns for the 'entries' table # in the same format you pass to DBIC's add_columns name => { data_type => "varchar", is_nullable => 1, # probably important }, ], ); $dir->search({ name => "foo" }); # SQL::Abstract
This backend for KiokuDB leverages existing DBI accessible databases.
The schema is based on two tables, entries and gin_index (the latter is only used if a Search::GIN extractor is specified).
entries
gin_index
The entries table has two main columns, id and data (currently in JSPON format, in the future the format will be pluggable), and additional user specified columns.
id
data
The user specified columns are extracted from inserted objects using a callback (or just copied for simple scalars), allowing SQL where clauses to be used for searching.
The columns are specified using a DBIx::Class::ResultSource instance.
One additional column info parameter is used, extract, which is called as a method on the inserted object with the column name as the only argument. The return value from this callback will be used to populate the column.
extract
If the column extractor is omitted then the column will contain a copy of the entry data key by the same name, if it is a plain scalar. Otherwise the column will be NULL.
NULL
These columns are only used for lookup purposes, only data is consulted when loading entries.
This driver has been tested with MySQL 5 (4.1 should be the minimal supported version), SQLite 3, and PostgresSQL 8.3.
The SQL code is reasonably portable and should work with most databases. Binary column support is required when using the Storable serializer.
For reasons of performance and ease of use database vendors ship with read committed transaction isolation by default.
This means that read locks are not acquired when data is fetched from the database, allowing it to be updated by another writer. If the current transaction then updates the value it will be silently overwritten.
IMHO this is a much bigger problem when the data is unstructured. This is because data is loaded and fetched in potentially smaller chunks, increasing the risk of phantom reads.
Unfortunately enabling truly isolated transaction semantics means that txn_commit may fail due to a lock contention, forcing you to repeat your transaction. Arguably this is more correct "read comitted", which can lead to race conditions.
txn_commit
Enabling repeatable read or serializable transaction isolation prevents transactions from interfering with eachother, by ensuring all data reads are performed with a shared lock.
For more information on isolation see http://en.wikipedia.org/wiki/Isolation_(computer_science)
SQLite provides serializable isolation by default.
http://www.sqlite.org/pragma.html#pragma_read_uncommitted
MySQL provides read committed isolation by default.
Serializable level isolation can be enabled by by default by changing the transaction-isolation global variable,
transaction-isolation
http://dev.mysql.com/doc/refman/5.1/en/set-transaction.html#isolevel_serializable
PostgreSQL provides read committed isolation by default.
Repeatable read or serializable isolation can be enabled by setting the default transaction isolation level, or using the SET TRANSACTION SQL statement.
SET TRANSACTION
http://www.postgresql.org/docs/8.3/interactive/transaction-iso.html, http://www.postgresql.org/docs/8.3/interactive/runtime-config-client.html#GUC-DEFAULT-TRANSACTION-ISOLATION
Created automatically.
This is DBIx::Class::Schema object that is used for schema deployment, connectivity and transaction handling.
An array reference whose contents are passed to "connect" in DBIx::Class::Schema.
If omitted will be created from the attrs dsn, user, password and dbi_attrs.
dsn
user
password
dbi_attrs
Convenience attrs for connecting using "connect" in KiokuDB.
User in connect_info's builder.
connect_info
Additional columns, see "COLUMN EXTRACTIONS".
KiokuDB::Serializer. Coerces from a string, too:
KiokuDB->connect("dbi:...", serializer => "storable");
Defaults to KiokuDB::Serializer::JSON.
If true the existence of the tables will be checked for and the DB will be deployed if not.
Defaults to false.
An optional Search::GIN::Extract used to create the gin_index entries.
Usually Search::GIN::Extract::Callback.
A hook that is called on the backend object as a method with the schema as the argument just before connecting.
If you need to modify the schema in some way (adding indexes or constraints) this is where it should be done.
See KiokuDB::Backend and the various roles for more info.
Calls "deploy" in DBIx::Class::Schema.
Deployment to MySQL requires that you specify something like:
$dir->backend->deploy({ producer_args => { mysql_version => 4 } });
because MySQL versions before 4 did not have support for boolean types, and the schema emitted by SQL::Translator will not work with the queries used.
Drops the entries and gin_index tables.
http://github.com/nothingmuch/kiokudb-backend-dbi
Yuval Kogman <nothingmuch@woobling.org>
Copyright (c) 2008, 2009 Yuval Kogman, Infinity Interactive. All rights reserved This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
To install KiokuDB::Backend::DBI, copy and paste the appropriate command in to your terminal.
cpanm
cpanm KiokuDB::Backend::DBI
CPAN shell
perl -MCPAN -e shell install KiokuDB::Backend::DBI
For more information on module installation, please visit the detailed CPAN module installation guide.