VoltDB is a Churning Urn of Groovy Funk
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Join For FreeThis article was originally written by Stefano Santoro
VoltDB is welcoming Groovy into its ecosystem as its first inline procedure language. Code your procedure logic straight into the DDL, bypassing the java procedure requirements to edit/compile java source files separately.
With VoltDB Groovy stored procedures, you can code your procedure implementation as part of CREATE PROCEDURE statements in your DDL file.
CREATE PROCEDURE groovy.procedures.Item AS ### selectItem = new SQLStmt('SELECT ITEM_ID, DESCRIPTION FROM ITEMS WHERE ITEM_ID = ?') transactOn = { id -> voltQueueSQL(selectItem, EXPECT_ZERO_OR_ONE_ROW, id) voltExecuteSQL(true) } ### LANGUAGE GROOVY; PARTITION PROCEDURE Item ON TABLE ITEMS COLUMN ITEM_ID;
How to write a groovy procedure
You can rely on the fact that the following imports are predefined and made available for your Groovy store procedures:
import static org.voltdb.VoltTypes.* import static org.voltdb.VoltProcedure.* import org.voltdb.* import org.voltdb.groovy.TableBuilder import org.voltdb.groovy.Tuplerator import org.voltdb.VoltProcedure.VoltAbortException
You first define instances of SQLStmt
that, like in
Java, must never change throughout the procedure code. This is because
VoltDB reflects on, analyzes, and creates plan for those statements.
You need, then, to define the transactOn
closure. VoltDB invokes this closure when it actually executes the procedure. The closure can accept any arguments that its java run method equivalent can. It also must return a VoltTable
, or an array of VoltTable
s, or a long value.
If you need to abort the transaction while the transactOn closure executes, then you need to throw the VoltAbortException
.
Also keep in mind the following guidelines.
- define your SQLStmt’s outside the
transactOn
closure - use tables to persist any state that must live across procedure invocations
Groovy Table Readers and Builders
The following procedure showcases two additions that make reading, and building a table a little easier
CREATE PROCEDURE voter.procedures.ContestantWinningStates AS ### resultStmt = new SQLStmt(''' SELECT contestant_number, state, SUM(num_votes) AS num_votes FROM v_votes_by_contestant_number_state GROUP BY contestant_number, state ORDER BY 2 ASC, 3 DESC, 1 ASC; ''') transactOn = { int contestantNumber, int max -> voltQueueSQL(resultStmt) results = [] state = "" tuplerator(voltExecuteSQL()[0]).eachRow { isWinning = state != it[1] state = it[1] if (isWinning && it[0] == contestantNumber) { results << [state: state, votes: it[2]] } } if (max > results.size) max = results.size buildTable(state:STRING, num_votes:BIGINT) { results.sort { a,b -> b.votes - a.votes }[0..<max].each { row it.state, it.votes } } } ### LANGUAGE GROOVY;
tuplerator(VoltTable table)
returns a Groovy wrapper around
the VoltTable. The eachRow method accepts a closure that is invoked for
each row in the table. Column values can easily be accessed by column
index, or column name. In the example above ‘it’ is the implicit
parameter passed to eachRow closure, and ‘it’ accesses the first column
value for the row with the it[0]
accessor. The same may be accessed with it['contestantNumber']
or more simply with it.contestantNumber
. If you need to access directly the underlying table, you may do so by referring it with the ‘table’ accessor: it.table.get(1,STRING)
. Other methods available to you are rowAt(int rowNum)
, which sets the table cursor to the indicated row, and reset()
, which resets the table cursor. For example
tuplerator(voltExecuteSQL()[0]).atRow(0)['state']
gets the state column value for the first row.
buildTable(column name: type map) allows you to build tables easily. The method parameters are:
- a map where the keys are column names, and the values are their respective column types.
- a closure where row invocations add rows to the underlying table
The code above shows a table with two columns (state, and num_votes), that is fed values from the results collection.
Both may be combined as follows, where the results of one table are processed, and fed into the newly built one:
CREATE PROCEDURE voter.procedures.GetStateHeatmap AS ### resultStmt = new SQLStmt(''' SELECT contestant_number, state, SUM(num_votes) AS num_votes FROM v_votes_by_contestant_number_state GROUP BY contestant_number, state ORDER BY 2 ASC, 3 DESC, 1 ASC; ''') transactOn = { voltQueueSQL(resultStmt) state = "" buildTable( state:STRING, contestant_number:INTEGER, num_votes:BIGINT, is_winning:TINYINT ) { tuplerator(voltExecuteSQL()[0]).eachRow { byte isWinning = state != it.state ? (byte)1 : (byte)0 state = it.state row state, it.contestantNumber, it.numVotes, isWinning } } } ### LANGUAGE GROOVY;
The above code excerpts may be perused by visiting an example DDL in our Github repository
Java Procedures are still faster than Groovy procedures
The syntactic conciseness that leverages the dynamic code interpretation capabilities of Groovy comes at a performance cost. Java should be your procedure implementation language choice if you really need to eek out as much performance as you can. But if you want something to get you started faster with VoltDB, and explore its features, and power, then Groovy procedures are a very good option.
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