[
https://issues.apache.org/jira/browse/DRILL-4363?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15141042#comment-15141042
]
ASF GitHub Bot commented on DRILL-4363:
---------------------------------------
Github user jinfengni commented on a diff in the pull request:
https://github.com/apache/drill/pull/371#discussion_r52476961
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/planner/logical/DrillPushLimitToScanRule.java
---
@@ -0,0 +1,107 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.drill.exec.planner.logical;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.calcite.plan.RelOptRule;
+import org.apache.calcite.plan.RelOptRuleCall;
+import org.apache.calcite.plan.RelOptRuleOperand;
+import org.apache.calcite.rel.RelNode;
+import org.apache.calcite.util.Pair;
+import org.apache.drill.exec.physical.base.GroupScan;
+import org.apache.drill.exec.planner.logical.partition.PruneScanRule;
+import org.apache.drill.exec.store.parquet.ParquetGroupScan;
+
+import java.io.IOException;
+import java.util.concurrent.TimeUnit;
+
+public abstract class DrillPushLimitToScanRule extends RelOptRule {
+ static final org.slf4j.Logger logger =
org.slf4j.LoggerFactory.getLogger(DrillPushLimitToScanRule.class);
+
+ private DrillPushLimitToScanRule(RelOptRuleOperand operand, String
description) {
+ super(operand, description);
+ }
+
+ public static DrillPushLimitToScanRule LIMIT_ON_SCAN = new
DrillPushLimitToScanRule(
+ RelOptHelper.some(DrillLimitRel.class,
RelOptHelper.any(DrillScanRel.class)), "DrillPushLimitToScanRule_LimitOnScan") {
+ @Override
+ public boolean matches(RelOptRuleCall call) {
+ DrillScanRel scanRel = call.rel(1);
+ return scanRel.getGroupScan() instanceof ParquetGroupScan; // It
only applies to Parquet.
+ }
+
+ @Override
+ public void onMatch(RelOptRuleCall call) {
+ DrillLimitRel limitRel = call.rel(0);
+ DrillScanRel scanRel = call.rel(1);
+ doOnMatch(call, limitRel, scanRel, null);
+ }
+ };
+
+ public static DrillPushLimitToScanRule LIMIT_ON_PROJECT = new
DrillPushLimitToScanRule(
+ RelOptHelper.some(DrillLimitRel.class,
RelOptHelper.some(DrillProjectRel.class,
RelOptHelper.any(DrillScanRel.class))),
"DrillPushLimitToScanRule_LimitOnProject") {
+ @Override
+ public boolean matches(RelOptRuleCall call) {
+ DrillScanRel scanRel = call.rel(2);
+ return scanRel.getGroupScan() instanceof ParquetGroupScan; // It
only applies to Parquet.
+ }
+
+ @Override
+ public void onMatch(RelOptRuleCall call) {
+ DrillLimitRel limitRel = call.rel(0);
+ DrillProjectRel projectRel = call.rel(1);
+ DrillScanRel scanRel = call.rel(2);
+ doOnMatch(call, limitRel, scanRel, projectRel);
+ }
+ };
+
+
+ protected void doOnMatch(RelOptRuleCall call, DrillLimitRel limitRel,
DrillScanRel scanRel, DrillProjectRel projectRel){
+ try {
+ final int rowCountRequested = (int) limitRel.getRows();
+
+ final Pair<GroupScan, Boolean> newGroupScanPair =
ParquetGroupScan.filterParquetScanByLimit((ParquetGroupScan)(scanRel.getGroupScan()),
rowCountRequested);
--- End diff --
I can change to use applyLimit(int maxRecords). This method will modify
the internal state of the groupscan and return true, if the limit is applied.
Otherwise, leave the groupscan instance unchanged and return false.
> Apply row count based pruning for parquet table in LIMIT n query
> ----------------------------------------------------------------
>
> Key: DRILL-4363
> URL: https://issues.apache.org/jira/browse/DRILL-4363
> Project: Apache Drill
> Issue Type: Improvement
> Reporter: Jinfeng Ni
> Assignee: Aman Sinha
> Fix For: 1.6.0
>
>
> In interactive data exploration use case, one common and probably first query
> that users would use is " SELECT * from table LIMIT n", where n is a small
> number. Such query will give user idea about the columns in the table.
> Normally, user would expect such query should be completed in very short
> time, since it's just asking for small amount of rows, without any
> sort/aggregation.
> When table is small, there is no big problem for Drill. However, when the
> table is extremely large, Drill's response time is not as fast as what user
> would expect.
> In case of parquet table, it seems that query planner could do a bit better
> job : by applying row count based pruning for such LIMIT n query. The
> pruning is kind of similar to what partition pruning will do, except that it
> uses row count, in stead of partition column values. Since row count is
> available in parquet table, it's possible to do such pruning.
> The benefit of doing such pruning is clear: 1) for small "n", such pruning
> would end up with a few parquet files, in stead of thousands, or millions of
> files to scan. 2) execution probably does not have to put scan into multiple
> minor fragments and start reading the files concurrently, which will cause
> big IO overhead. 3) the physical plan itself is much smaller, since it does
> not include the long list of parquet files, reduce rpc cost of sending the
> fragment plans to multiple drillbits, and the overhead to
> serialize/deserialize the fragment plans.
>
>
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
