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[fix](planner) query should be cancelled if limit reached (apache#44338)
Problem Summary:
When there is a `limit` cluse in SQL, if FE has obtained data with more
than the `limit` number of rows,
it should send a cancel command to BE to cancel the query to prevent BE
from reading more data.
However, this function has problems in the current code and does not
work.
Especially in external table query, this may result in lots of
unnecessary network io read.
1. `isBlockQuery`
In the old optimizer, if a query statement contains a `sort` or `agg`
node,
`isBlockQuery` will be marked as true, otherwise it will be false.
In the new optimizer, this value is always true.
Regardless of the old or new optimizer, this logic is wrong.
But only when `isBlockQuery = false` will the reach limit logic be
triggered.
2. Calling problem of reach limit logic
The reach limit logic judgment will only be performed when `eos = true`
in the rowBatch returned by BE.
This is wrong.
Because for `limit N` queries, each BE's own `limit` is N. But for FE,
as long as the total number of rows
returned by all BEs exceeds N, the reach limit logic can be triggered.
So it should not be processed only when `eos = true`.
The PR mainly changes:
1. Remove `isBlockQuery`
`isBlockQuery` is only used in the reach limit logic. And it is not
needed. Remove it completely.
2. Modify the judgment position of reach limit.
When the number of rows obtained by FE is greater than the limit,
it will check the reach limit logic.
3. fix wrong `limitRows` in `QueryProcessor`
the limitRows should be got from the first fragment, not last.
4. In scanner scheduler on BE side, if scanner has limit, ignore the
scan bytes threshold per round.
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54 changes: 54 additions & 0 deletions
54
fe/fe-core/src/main/java/org/apache/doris/qe/LimitUtils.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,54 @@ | ||
| // 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.doris.qe; | ||
|
|
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| import org.apache.doris.common.Status; | ||
| import org.apache.doris.thrift.TStatusCode; | ||
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| import org.apache.logging.log4j.LogManager; | ||
| import org.apache.logging.log4j.Logger; | ||
|
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| import java.util.function.Consumer; | ||
|
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| /** | ||
| * This is a utility class for limit related operations. | ||
| * Because current there are 2 places need to check limit rows, so put the logic here for unification. | ||
| * - Coordinator.getNext(); | ||
| * - QueryProcessor.getNext(); | ||
| */ | ||
| public class LimitUtils { | ||
| private static final Logger LOG = LogManager.getLogger(LimitUtils.class); | ||
| private static final Status LIMIT_REACH_STATUS = new Status(TStatusCode.LIMIT_REACH, "query reach limit"); | ||
|
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| // if reached limit rows, cancel this query immediately | ||
| // to avoid BE from reading more data. | ||
| public static boolean cancelIfReachLimit(RowBatch resultBatch, long limitRows, long numReceivedRows, | ||
| Consumer<Status> cancelFunc) { | ||
| boolean reachedLimit = false; | ||
| if (limitRows > 0 && numReceivedRows >= limitRows) { | ||
| if (LOG.isDebugEnabled()) { | ||
| LOG.debug("reach limit rows: {}, received rows: {}, cancel query", limitRows, numReceivedRows); | ||
| } | ||
| cancelFunc.accept(LIMIT_REACH_STATUS); | ||
| // set this | ||
| resultBatch.setEos(true); | ||
| reachedLimit = true; | ||
| } | ||
| return reachedLimit; | ||
| } | ||
| } |
59 changes: 59 additions & 0 deletions
59
fe/fe-core/src/test/java/org/apache/doris/qe/LimitUtilsTest.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,59 @@ | ||
| // 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.doris.qe; | ||
|
|
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|
|
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| import org.apache.doris.common.Status; | ||
|
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| import org.junit.Assert; | ||
| import org.junit.Test; | ||
|
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| import java.util.function.Consumer; | ||
|
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| public class LimitUtilsTest { | ||
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| private static int res = 0; | ||
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| @Test | ||
| public void testUpperBound() { | ||
| Consumer<Status> cancelFunc = batch -> res = 666; | ||
| RowBatch rowBatch = new RowBatch(); | ||
| rowBatch.setEos(false); | ||
| // - no limit | ||
| Assert.assertFalse(LimitUtils.cancelIfReachLimit(rowBatch, 0, 10, cancelFunc)); | ||
| Assert.assertFalse(rowBatch.isEos()); | ||
| Assert.assertEquals(0, res); | ||
|
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| // - not reach limit | ||
| Assert.assertFalse(LimitUtils.cancelIfReachLimit(rowBatch, 10, 1, cancelFunc)); | ||
| Assert.assertFalse(rowBatch.isEos()); | ||
| Assert.assertEquals(0, res); | ||
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| // - reach limit | ||
| Assert.assertTrue(LimitUtils.cancelIfReachLimit(rowBatch, 10, 10, cancelFunc)); | ||
| Assert.assertTrue(rowBatch.isEos()); | ||
| Assert.assertEquals(666, res); | ||
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| // - reach limit | ||
| res = 0; | ||
| rowBatch.setEos(false); | ||
| Assert.assertTrue(LimitUtils.cancelIfReachLimit(rowBatch, 10, 100, cancelFunc)); | ||
| Assert.assertTrue(rowBatch.isEos()); | ||
| Assert.assertEquals(666, res); | ||
| } | ||
| } |