Description:

Generates SQL select queries that fetch “pages” of rows from a table. The partition size property, along with the table’s row count, determine the size and number of pages and generated FlowFiles. In addition, incremental fetching can be achieved by setting Maximum-Value Columns, which causes the processor to track the columns’ maximum values, thus only fetching rows whose columns’ values exceed the observed maximums. This processor is intended to be run on the Primary Node only.

Tags:

sql, select, jdbc, query, database, fetch, generate

Properties:

In the list below, the names of required properties appear in bold. Any other properties (not in bold) are considered optional. The table also indicates any default values, and whether a property supports the Expression Language Guide.

Name Default Value Allowable Values Description
Database Connection Pooling Service Controller Service API: DBCPService
Implementations:
HiveConnectionPool
DBCPConnectionPool
The Controller Service that is used to obtain a connection to the database.
Database Type Generic *Generic
*Oracle
The type/flavor of database, used for generating database-specific code. In many cases the Generic type should suffice, but some databases (such as Oracle) require custom SQL clauses.
Table Name The name of the database table to be queried.
Columns to Return A comma-separated list of column names to be used in the query. If your database requires special treatment of the names (quoting, e.g.), each name should include such treatment. If no column names are supplied, all columns in the specified table will be returned.
Maximum-value Columns A comma-separated list of column names. The processor will keep track of the maximum value for each column that has been returned since the processor started running. Using multiple columns implies an order to the column list, and each column's values are expected to increase more slowly than the previous columns' values. Thus, using multiple columns implies a hierarchical structure of columns, which is usually used for partitioning tables. This processor can be used to retrieve only those rows that have been added/updated since the last retrieval. Note that some JDBC types such as bit/boolean are not conducive to maintaining maximum value, so columns of these types should not be listed in this property, and will result in error(s) during processing. If no columns are provided, all rows from the table will be considered, which could have a performance impact.
Max Wait Time 0 seconds The maximum amount of time allowed for a running SQL select query , zero means there is no limit. Max time less than 1 second will be equal to zero.
Partition Size 10000 The number of result rows to be fetched by each generated SQL statement. The total number of rows in the table divided by the partition size gives the number of SQL statements (i.e. FlowFiles) generated. A value of zero indicates that a single FlowFile is to be generated whose SQL statement will fetch all rows in the table.

Relationships:

Name Description
success Successfully created FlowFile from SQL query result set.
failure This relationship is only used when SQL query execution (using an incoming FlowFile) failed. The incoming FlowFile will be penalized and routed to this relationship. If no incoming connection(s) are specified, this relationship is unused.

Reads Attributes:

None specified.

Writes Attributes:

Name Description
generatetablefetch.sql.error If the processor has incoming connections, and processing an incoming flow file causes a SQL Exception, the flow file is routed to failure and this attribute is set to the exception message.
generatetablefetch.tableName The name of the database table to be queried.
generatetablefetch.columnNames The comma-separated list of column names used in the query.
generatetablefetch.whereClause Where clause used in the query to get the expected rows.
generatetablefetch.maxColumnNames The comma-separated list of column names used to keep track of data that has been returned since the processor started running.
generatetablefetch.limit The number of result rows to be fetched by the SQL statement.
generatetablefetch.offset Offset to be used to retrieve the corresponding partition.

State management:

Scope Description
CLUSTER After performing a query on the specified table, the maximum values for the specified column(s) will be retained for use in future executions of the query. This allows the Processor to fetch only those records that have max values greater than the retained values. This can be used for incremental fetching, fetching of newly added rows, etc. To clear the maximum values, clear the state of the processor per the State Management documentation

Restricted:

This component is not restricted.

Input requirement:

This component allows an incoming relationship.

See Also:

QueryDatabaseTable, ExecuteSQL, ListDatabaseTables