/**
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Created on Aug 28, 2012
*/
package com.bigdata.rdf.sparql.ast;
import com.bigdata.bop.controller.SubqueryOp;
/**
* Used to specify the query plan for FILTER (NOT) EXISTS. There are two basic
* plans: vectored sub-plan and subquery with LIMIT ONE. Each plan has its
* advantages.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
*
* @see <a href="http://trac.blazegraph.com/ticket/988"> bad performance for FILTER
* EXISTS </a>
*/
public enum FilterExistsModeEnum {
/**
* This evaluation mode builds a hash index from all source solutions,
* vectors the solutions from the hash index into the sub-plan, and the does
* a hash join of the sub-plan with the hash index to determine which
* solutions pass the filter.
* <p>
* This plan solves the FILTER (NOT) EXISTS for multiple source solutions at
* the same time (vectoring). It is more efficient if the sub-plan requires
* relatively little work per solution to fully evaluate the sub-plan and
* there are a large number of solutions flowing into the FILTER (NOT)
* EXISTS.
*/
VectoredSubPlan,
/**
* This evaluation mode routes each source solution (one by one) into a
* separate {@link SubqueryOp subquery} and imposes a LIMIT ONE.
* <p>
* This plan is more efficient if there are many solutions to the FILTER for
* each source solution, if it is relatively expensive to find all such
* solutions, and if there are relatively few source solutions. Under these
* conditions, the FILTER (NOT) EXISTS sub-query is cutoff once it finds the
* first solution to each source solution and the overhead of submitting
* multiple sub-queries is modest because there are not that many source
* solution that need to flow into the FILTER.
*/
SubQueryLimitOne;
}