Provided by: libkiokudb-backend-dbi-perl_1.22-1_all 
NAME
KiokuDB::Backend::DBI - DBI backend for KiokuDB
SYNOPSIS
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
DESCRIPTION
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).
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.
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.
COLUMN EXTRACTIONS
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.
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".
These columns are only used for lookup purposes, only "data" is consulted when loading
entries.
DBIC INTEGRATION
This backend is layered on top of DBIx::Class::Storage::DBI and reused DBIx::Class::Schema
for DDL.
Because of this objects from a DBIx::Class::Schema can refer to objects in the KiokuDB
entries table, and vice versa.
For more details see DBIx::Class::Schema::KiokuDB.
SUPPORTED DATABASES
This driver has been tested with MySQL 5 (4.1 should be the minimal supported version),
SQLite 3, and PostgreSQL 8.3.
The SQL code is reasonably portable and should work with most databases. Binary column
support is required when using the Storable serializer.
Transactions
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.
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
SQLite provides serializable isolation by default.
<http://www.sqlite.org/pragma.html#pragma_read_uncommitted>
MySQL
MySQL provides read committed isolation by default.
Serializable level isolation can be enabled by by default by changing the
"transaction-isolation" global variable,
<http://dev.mysql.com/doc/refman/5.1/en/set-transaction.html#isolevel_serializable>
PostgreSQL
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.
<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>
ATTRIBUTES
schema
Created automatically.
This is DBIx::Class::Schema object that is used for schema deployment, connectivity
and transaction handling.
connect_info
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.
columns
Additional columns, see "COLUMN EXTRACTIONS".
serializer
KiokuDB::Serializer. Coerces from a string, too:
KiokuDB->connect("dbi:...", serializer => "storable");
Defaults to KiokuDB::Serializer::JSON.
create
If true the existence of the tables will be checked for and the DB will be deployed if
not.
Defaults to false.
extract
An optional Search::GIN::Extract used to create the "gin_index" entries.
Usually Search::GIN::Extract::Callback.
schema_hook
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.
for_update
If true (the defaults), will cause all select statement to be issued with a "FOR
UPDATE" modifier on MySQL, Postgres and Oracle.
This is highly reccomended because these database provide low isolation guarantees as
configured out the box, and highly interlinked graph databases are much more
susceptible to corruption because of lack of transcational isolation than normalized
relational databases.
sqlite_sync_mode
If this attribute is set and the underlying database is SQLite, then "PRAGMA
syncrhonous=..." will be issued with this value.
Can be "OFF", "NORMAL" or "FULL" (SQLite's default), or 0, 1, or 2.
See <http://www.sqlite.org/pragma.html#pragma_synchronous>.
mysql_strict
If true (the default), sets MySQL's strict mode.
This is HIGHLY reccomended, or you may enjoy some of MySQL's more interesting
features, like automatic data loss when the columns are too narrow.
See <http://dev.mysql.com/doc/refman/5.0/en/server-sql-mode.html> and
DBIx::Class::Storage::DBI::mysql for more details.
on_connect_call
See DBIx::Class::Storage::DBI.
This attribute is constructed based on the values of "mysql_version" and
"sqlite_sync_mode", but may be overridden if you need more control.
dbic_attrs
See DBIx::Class::Storage::DBI.
Defaults to
{ on_connect_call => $self->on_connect_call }
batch_size
SQL that deals with entries run in batches of the amount provided in "batch_size". If
it is not provided, the statements will run in a single batch.
This solves the issue with SQLite where lists can only handle 999 elements at a time.
"batch_size" will be set to 999 by default if the driver in use is SQLite.
METHODS
See KiokuDB::Backend and the various roles for more info.
deploy
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.
drop_tables
Drops the "entries" and "gin_index" tables.
TROUBLESHOOTING
I get "unexpected end of string while parsing JSON string"
You are problably using MySQL, which comes with a helpful data compression feature: when
your serialized objects are larger than the maximum size of a "BLOB" column MySQL will
simply shorten it for you.
Why "BLOB" defaults to 64k, and how on earth someone would consider silent data truncation
a sane default I could never fathom, but nevertheless MySQL does allow you to disable this
by setting the "strict" SQL mode in the configuration.
To resolve the actual problem (though this obviously won't repair your lost data), alter
the entries table so that the "data" column uses the nonstandard "LONGBLOB" datatype.
VERSION CONTROL
<http://github.com/nothingmuch/kiokudb-backend-dbi>
AUTHOR
Yuval Kogman <nothingmuch@woobling.org>
COPYRIGHT
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.