| <?xml version="1.0" encoding="UTF-8"?> |
| <!-- |
| 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. |
| --> |
| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
| <concept id="default_spillable_buffer_size" rev="2.10.0 IMPALA-3200"> |
| |
| <title>DEFAULT_SPILLABLE_BUFFER_SIZE Query Option</title> |
| <titlealts audience="PDF"><navtitle>DEFAULT_SPILLABLE_BUFFER_SIZE</navtitle></titlealts> |
| <prolog> |
| <metadata> |
| <data name="Category" value="Impala"/> |
| <data name="Category" value="Impala Query Options"/> |
| <data name="Category" value="Querying"/> |
| <data name="Category" value="Developers"/> |
| <data name="Category" value="Data Analysts"/> |
| </metadata> |
| </prolog> |
| |
| <conbody> |
| |
| <p> |
| <indexterm audience="hidden">DEFAULT_SPILLABLE_BUFFER_SIZE query option</indexterm> |
| Specifies the default size for a memory buffer used when the |
| spill-to-disk mechanism is activated, for example for queries against |
| a large table with no statistics, or large join operations. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/type_integer"/> |
| |
| <!-- DEFAULT_SPILLABLE_BUFFER_SIZE: [2097152] --> |
| |
| <p conref="../shared/impala_common.xml#common/default_blurb"/> |
| <p> |
| <codeph>2097152</codeph> (2 MB) |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/units_blurb"/> |
| |
| <p conref="../shared/impala_common.xml#common/added_in_2100"/> |
| |
| <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/> |
| <p> |
| This query option sets an upper bound on the size of the internal |
| buffer size that can be used during spill-to-disk operations. The |
| actual size of the buffer is chosen by the query planner. |
| </p> |
| <p> |
| If overall query performance is limited by the time needed for spilling, |
| consider increasing the <codeph>DEFAULT_SPILLABLE_BUFFER_SIZE</codeph> setting. |
| Larger buffer sizes result in Impala issuing larger I/O requests to storage |
| devices, which might result in higher throughput, particularly on rotational |
| disks. |
| </p> |
| <p> |
| The tradeoff with a large value for this setting is increased memory usage during |
| spill-to-disk operations. Reducing this value may reduce memory consumption. |
| </p> |
| <p> |
| To determine if the value for this setting is having an effect by capping the |
| spillable buffer size, you can see the buffer size chosen by the query planner for |
| a particular query. <codeph>EXPLAIN</codeph> the query while the setting |
| <codeph>EXPLAIN_LEVEL=2</codeph> is in effect. |
| </p> |
| |
| <p conref="../shared/impala_common.xml#common/example_blurb"/> |
| |
| <codeblock><![CDATA[ |
| set default_spillable_buffer_size=4MB; |
| ]]> |
| </codeblock> |
| |
| <p conref="../shared/impala_common.xml#common/related_info"/> |
| <p> |
| <xref keyref="buffer_pool_limit"/>, |
| <xref keyref="max_row_size"/>, |
| <xref keyref="min_spillable_buffer_size"/>, |
| <xref keyref="scalability_buffer_pool"/> |
| </p> |
| |
| </conbody> |
| </concept> |