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d484d2f684
This now gives a clean RAT check with bin/check-rat-report.py, which is one way for the Impala community to check compliance with ASF rules on intellectual property. Change-Id: I2ad06435f84a65ba126759e42a18fdaf52cd7036 Reviewed-on: http://gerrit.cloudera.org:8080/5232 Reviewed-by: Jim Apple <jbapple-impala@apache.org> Tested-by: Impala Public Jenkins Reviewed-by: John Russell <jrussell@cloudera.com>
78 lines
3.5 KiB
XML
78 lines
3.5 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!--
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Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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-->
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept rev="1.2.1" id="sync_ddl">
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<title>SYNC_DDL Query Option</title>
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<titlealts audience="PDF"><navtitle>SYNC_DDL</navtitle></titlealts>
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<prolog>
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<metadata>
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<data name="Category" value="Impala"/>
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<data name="Category" value="Impala Query Options"/>
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<data name="Category" value="DDL"/>
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<data name="Category" value="SQL"/>
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<data name="Category" value="Developers"/>
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<data name="Category" value="Data Analysts"/>
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</metadata>
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</prolog>
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<conbody>
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<p>
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<indexterm audience="Cloudera">SYNC_DDL query option</indexterm>
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When enabled, causes any DDL operation such as <codeph>CREATE TABLE</codeph> or <codeph>ALTER TABLE</codeph>
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to return only when the changes have been propagated to all other Impala nodes in the cluster by the Impala
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catalog service. That way, if you issue a subsequent <codeph>CONNECT</codeph> statement in
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<cmdname>impala-shell</cmdname> to connect to a different node in the cluster, you can be sure that other
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node will already recognize any added or changed tables. (The catalog service automatically broadcasts the
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DDL changes to all nodes automatically, but without this option there could be a period of inconsistency if
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you quickly switched to another node, such as by issuing a subsequent query through a load-balancing proxy.)
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</p>
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<p>
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Although <codeph>INSERT</codeph> is classified as a DML statement, when the <codeph>SYNC_DDL</codeph> option
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is enabled, <codeph>INSERT</codeph> statements also delay their completion until all the underlying data and
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metadata changes are propagated to all Impala nodes. Internally, Impala inserts have similarities with DDL
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statements in traditional database systems, because they create metadata needed to track HDFS block locations
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for new files and they potentially add new partitions to partitioned tables.
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</p>
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<note>
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Because this option can introduce a delay after each write operation, if you are running a sequence of
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<codeph>CREATE DATABASE</codeph>, <codeph>CREATE TABLE</codeph>, <codeph>ALTER TABLE</codeph>,
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<codeph>INSERT</codeph>, and similar statements within a setup script, to minimize the overall delay you can
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enable the <codeph>SYNC_DDL</codeph> query option only near the end, before the final DDL statement.
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</note>
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<p conref="../shared/impala_common.xml#common/type_boolean"/>
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<p conref="../shared/impala_common.xml#common/default_false_0"/>
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<!-- To do:
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Example could be useful here.
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-->
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<p conref="../shared/impala_common.xml#common/related_info"/>
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<p>
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<xref href="impala_ddl.xml#ddl"/>
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</p>
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</conbody>
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</concept>
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