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13.10. Apache Accumulo Translator

The Apache Accumulo Translator, known by the type name accumulo, exposes querying functionality to Accumulo Data Sources. Apache Accumulo is a sorted, distributed key value store with robust, scalable, high performance data storage and retrieval system. This translator provides an easy way connect to Accumulo system and provides relational way using SQL to add records from directly from user or from other sources that are integrated with Teiid. It also gives ability to read/update/delete existing records from Accumulo store. Teiid has capability to pass-in logged in user's roles as visibility properties to restrict the data access.
Here are some use cases for this translator:
  • Accumulo source can be used in Teiid, to continually add/update the documents in the Accumulo system from other sources automatically.
  • Access Accumulo through SQL interface.
  • Make use of cell level security through enterprise roles.
  • Accumulo translator can be used as an indexing system to gather data from other enterprise sources such as RDBMS, Web Service, SalesForce etc, all in single client call transparently with out any coding.
Apache Accumulo is distributed key value store with unique data model. It allows to group its key-value pairs in a collection called "table". You can define a schema representing Accumulo table structures in Teiid using DDL or using Teiid Designer with help of metadata extension properties defined below. Since no data type information is defined on the columns, by default all columns are considered as string data types. However, during modeling of the schema, one can use various other data types supported through Teiid to define a data type of column, that user wishes to expose.Once this schema is defined and exposed through VDB in a Teiid database, and Accumulo Data Sources is created, the user can issue "INSERT/UPDATE/DELETE" based SQL calls to insert/update/delete records into the Accumulo, and issue "SELECT" based calls to retrieve records from Accumulo. You can use full range of SQL with Teiid system integrating other sources along with Accumulo source.

Important

By default, Accumulo table structure is flat and thus can not define relationships among tables. So, a SQL JOIN is performed in Teiid layer rather than pushed to source even if both tables on either side of the JOIN reside in the Accumulo. Currently any criteria based on EQUALITY and/or COMPARISON using complex AND/OR clauses are handled by Accumulo translator and will be properly executed at source.
Here is an example Dynamic VDB that shows the Accumulo translator: 
<vdb name="myvdb" version="1">
    <model name="accumulo">
        <source name="node-one" translator-name="accumulo" connection-jndi-name="java:/accumuloDS"/>
    </model>
<vdb>
The translator does NOT provide a connection to the Accumulo. For that purpose, Teiid has a JCA adapter that provides a connection to Accumulo using Accumulo Java libraries.
If you are using the Designer Tooling, to create a VDB create/use a Teiid Designer Model project, use the "Teiid Connection- Source Model" importer, create Accumulo Data Source using data source creation wizard and use accumulo as translator in the importer. The table is created in a source model by the time you finish with this importer. Create a VDB and deploy into Teiid Server and use either jdbc, odbc or odata to query.
The Accumulo translator is capable of traversing through Accumulo table structures and build a metadata structure for Teiid translator. The schema importer can understand simple tables by traversing a single ROWID of data, then looks for all the unique keys, based on it and comes up with a tabular structure for Accumulo based table. Using the following import properties, you can further refine the import behavior.

Table 13.5. Registry Properties

Property Name Description Required? Default
ColumnNamePattern
How the column name is to be formed
false
{CF}_{CQ}
ValueIn
Where the value for column is defined CQ or VALUE
false
{VALUE}

Note

{CQ}, {CF}, {ROWID} are expressions that you can use to define above properties in any pattern, and respective values of Column Qualifer, Column Familiy or ROWID will be replaced at import time. ROW ID of the Accumulo table, is automatically created as ROWID column, and will be defined as Primary Key on the table.
You can also define the metadata for the Accumulo based model, using DDL or using the Teiid Designer. When doing such exercise, the Accumulo Translator currently defines following extended metadata properties to be defined on its Teiid schema model to guide the translator to make proper decisions. The following properties are described under NAMESPACE "http://www.teiid.org/translator/accumulo/2013", for user convenience this namespace has alias name teiid_accumulo defind in Teiid. To define a extension property use expression like "teiid_accumulo:{property-name} value". All the properties below are intended to be used as OPTION properties on COLUMNS. See DDL Metadata for more information on defining DDL based metadata.

Table 13.6. Registry Properties

Property Name Description Required? Default
CF
Column Family
true
none
CQ
Column Qualifier
false
empty
VALUE-IN
Value of column defined in. Possible values (VALUE, CQ)
false
VALUE
Here is an example for a table called "User". A scan returns the following data: 
root@teiid> table User
root@teiid User> scan
  1 name:age []    43
  1 name:firstname []   John
  1 name:lastname []    Does
  2 name:age []    10
  2 name:firstname []   Jane
  2 name:lastname []    Smith
  3 name:age []    13
  3 name:firstname []   Mike
  3 name:lastname []    Davis
If you used the default importer from the Accumulo translator(like Dynamic VDB defined above), the table generated will look like this: 
CREATE FOREIGN TABLE "User" (
    rowid string OPTIONS (UPDATABLE FALSE, SEARCHABLE 'All_Except_Like'),
    name_age string OPTIONS (SEARCHABLE 'All_Except_Like', "teiid_accumulo:CF" 'name', "teiid_accumulo:CQ" 'age', "teiid_accumulo:VALUE-IN" '{VALUE}'),
    name_firstname string OPTIONS (SEARCHABLE 'All_Except_Like', "teiid_accumulo:CF" 'name', "teiid_accumulo:CQ" 'firstname', "teiid_accumulo:VALUE-IN" '{VALUE}'),
    name_lastname string OPTIONS (SEARCHABLE 'All_Except_Like', "teiid_accumulo:CF" 'name', "teiid_accumulo:CQ" 'lastname', "teiid_accumulo:VALUE-IN" '{VALUE}'),
    CONSTRAINT PK0 PRIMARY KEY(rowid)
) OPTIONS (UPDATABLE TRUE);
You can use "Import Property" as "ColumnNamePattern" as "{CQ}" will generate the following (note the names of the column): 
CREATE FOREIGN TABLE "User" (
    rowid string OPTIONS (UPDATABLE FALSE, SEARCHABLE 'All_Except_Like'),
    age string OPTIONS (SEARCHABLE 'All_Except_Like', "teiid_accumulo:CF" 'name', "teiid_accumulo:CQ" 'age', "teiid_accumulo:VALUE-IN" '{VALUE}'),
    firstname string OPTIONS (SEARCHABLE 'All_Except_Like', "teiid_accumulo:CF" 'name', "teiid_accumulo:CQ" 'firstname', "teiid_accumulo:VALUE-IN" '{VALUE}'),
    lastname string OPTIONS (SEARCHABLE 'All_Except_Like', "teiid_accumulo:CF" 'name', "teiid_accumulo:CQ" 'lastname', "teiid_accumulo:VALUE-IN" '{VALUE}'),
    CONSTRAINT PK0 PRIMARY KEY(rowid)
) OPTIONS (UPDATABLE TRUE);
If the column name is defined by Column Family, you can use "ColumnNamePattern" as "{CF}", and if the value for that column exists in the Column Qualifier then you can use "ValueIn" as "{CQ}". Using import properties you can dictate how the table is to b= be modeled. If you did not use built in import (not using Teiid Designer's Teiid Connection >> Source Model or Dynamic VDB), and would like to manually design the table in Designer then you must make sure you supply the Extension Metadata Properties defined above on the User table's columns from Accumulo extended metadata(In Designer, right-click on Model, and select "Model Extension Definitions" and select Accumulo. For example on FirstName column, you would supply
The Red Hat JBoss Data Virtualization-specific Accumulo Resource Adapter must be used with this translator.
You cannot perform native queries or use direct query procedures with this translator.