docs/topics/impala_timeouts.xml - impala - Git at Google

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 <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
 <concept rev="1.2.1" id="timeouts">

   <title>Setting Timeout Periods for Daemons, Queries, and Sessions</title>

   <titlealts audience="PDF">

     <navtitle>Setting Timeouts</navtitle>

   </titlealts>

   <prolog>
     <metadata>
       <data name="Category" value="Impala"/>
       <data name="Category" value="Administrators"/>
       <data name="Category" value="Scheduling"/>
       <data name="Category" value="Scalability"/>
     </metadata>
   </prolog>

   <conbody>

     <p>
       Depending on how busy your <keyword keyref="distro"/> cluster is, you might increase or decrease various timeout
       values. Increase timeouts if Impala is cancelling operations prematurely, when the system
       is responding slower than usual but the operations are still successful if given extra
       time. Decrease timeouts if operations are idle or hanging for long periods, and the idle
       or hung operations are consuming resources and reducing concurrency.
     </p>

     <p outputclass="toc inpage"/>

   </conbody>

   <concept id="statestore_timeout">

     <title>Increasing the Statestore Timeout</title>

     <conbody>

       <p rev="IMP-1210">
         If you have an extensive Impala schema, for example with hundreds of databases, tens of
         thousands of tables, and so on, you might encounter timeout errors during startup as the
         Impala catalog service broadcasts metadata to all the Impala nodes using the statestore
         service. To avoid such timeout errors on startup, increase the statestore timeout value
         from its default of 10 seconds. Specify the timeout value using the
         <codeph>-statestore_subscriber_timeout_seconds</codeph> option for the statestore
         service, using the configuration instructions in
         <xref href="impala_config_options.xml#config_options"/>. The symptom of this problem is
         messages in the <codeph>impalad</codeph> log such as:
       </p>

 <codeblock>Connection with state-store lost
 Trying to re-register with state-store</codeblock>

       <p>
         See <xref href="impala_scalability.xml#statestore_scalability"/> for more details about
         statestore operation and settings on clusters with a large number of Impala-related
         objects such as tables and partitions.
       </p>

     </conbody>

   </concept>

   <concept id="impalad_timeout">

     <title>Setting the Idle Query and Idle Session Timeouts for impalad</title>

     <conbody>

       <p>
         To keep long-running queries or idle sessions from tying up cluster resources, you can
         set timeout intervals for both individual queries, and entire sessions.
       </p>

       <note conref="../shared/impala_common.xml#common/timeout_clock_blurb"/>

       <p>
         Use the following startup options for the <cmdname>impalad</cmdname>
         daemon to specify timeout values:
       </p>

       <ul>
         <li><codeph>--idle_query_timeout</codeph>
           <p>
             Specifies the time in
             seconds after which an idle query is cancelled. This could be a
             query whose results were all fetched but was never closed, or one
             whose results were partially fetched and then the client program
             stopped requesting further results. This condition is most likely to
             occur in a client program using the JDBC or ODBC interfaces, rather
             than in the interactive <cmdname>impala-shell</cmdname> interpreter.
             Once a query is cancelled, the client program cannot retrieve any
             further results from the query.
           </p>
           <p rev="2.0.0">
             You can reduce
             the idle query timeout by using the <codeph>QUERY_TIMEOUT_S</codeph>
             query option. Any non-zero value specified for the
               <codeph>--idle_query_timeout</codeph> startup option serves as an
             upper limit for the <codeph>QUERY_TIMEOUT_S</codeph> query option.
             See <xref href="impala_query_timeout_s.xml#query_timeout_s"/> about
             the query option.
           </p>
           <p rev="2.0.0">A zero value for
               <codeph>--idle_query_timeout</codeph> disables query timeouts.
           </p>
           <p>
             Cancelled queries remain in the open state but use only the
             minimal resources.
           </p>
         </li>

         <li><codeph>--idle_session_timeout</codeph>
           <p>
             Specifies the time in
             seconds after which an idle session expires. A session is idle when
             no activity is occurring for any of the queries in that session, and
             the session has not started any new queries. Once a session is
             expired, you cannot issue any new query requests to it. The session
             remains open, but the only operation you can perform is to close it.
           </p>
           <p>
             The default value of 0 specifies sessions never
             expire.
           </p>
           <p rev="2.12.0">
             You can override the
               <codeph>--idle_session_timeout</codeph> value with the <xref
               href="impala_idle_session_timeout.xml#idle_session_timeout"/> at
             the session level.
           </p>
         </li>
       </ul>

       <p>
         For instructions on changing <cmdname>impalad</cmdname> startup options, see
         <xref href="impala_config_options.xml#config_options"/>.
       </p>

       <note>
         <p rev="IMPALA-5108">
           Impala checks periodically for idle sessions and queries
           to cancel. The actual idle time before cancellation might be up to 50% greater than
           the specified configuration setting. For example, if the timeout setting was 60, the
           session or query might be cancelled after being idle between 60 and 90 seconds.
         </p>
       </note>

     </conbody>

   </concept>
   <concept id="concept_rfy_jl1_rx">
     <title>Setting Timeout and Retries for Thrift Connections to the Backend
       Client</title>
     <conbody>
       <p>Impala connections to the backend client are subject to failure in
         cases when the network is momentarily overloaded. To avoid failed
         queries due to transient network problems, you can configure the number
         of Thrift connection retries using the following option: </p>
       <ul id="ul_bj3_ql1_rx">
         <li>The <codeph>--backend_client_connection_num_retries</codeph> option
           specifies the number of times Impala will try connecting to the
           backend client after the first connection attempt fails. By default,
             <cmdname>impalad</cmdname> will attempt three re-connections before
           it returns a failure. </li>
       </ul>
       <p>You can configure timeouts for sending and receiving data from the
         backend client. Therefore, if for some reason a query hangs, instead of
         waiting indefinitely for a response, Impala will terminate the
         connection after a configurable timeout.</p>
       <ul id="ul_vm2_2v1_rx">
         <li>The <codeph>--backend_client_rpc_timeout_ms</codeph> option can be
           used to specify the number of milliseconds Impala should wait for a
           response from the backend client before it terminates the connection
           and signals a failure. The default value for this property is 300000
           milliseconds, or 5 minutes. </li>
       </ul>
     </conbody>
   </concept>

   <concept id="cancel_query">

     <title>Cancelling a Query</title>

     <conbody>
       <p> Occasionally, an Impala query might run for an unexpectedly long time,
         tying up resources in the cluster. This section describes the options to
         terminate such runaway queries.</p>
     </conbody>
     <concept id="cancel_query_with_query_option">
       <title>Setting a Time Limit on Query Execution</title>
       <conbody>
         <p>An Impala administrator can set a default value of the
             <codeph>EXEC_TIME_LIMIT_S</codeph> query option for a resource pool.
           If a user accidentally runs a large query that executes for longer
           than the limit, it will be automatically terminated after the time
           limit expires to free up resources. </p>
         <p>You can override the default value per query or per session if you do
           not want to apply the default <codeph>EXEC_TIME_LIMIT_S</codeph> value
           to a specific query or a session. See <xref
             href="impala_exec_time_limit_s.xml#exec_time_limit_s"/> for the
           details of the query option.</p>
       </conbody>
     </concept>
     <concept id="cancel_query_in_webUI">
       <title>Interactively Cancelling a Query </title>
       <conbody>
         <p> You can cancel the query explicitly, independent of the timeout
           period, by going into the web UI for the <cmdname>impalad</cmdname>
           host (on port 25000 by default), and using the link on the
             <codeph>/queries</codeph> tab to cancel the running query. </p>
         <p> Various client applications let you interactively cancel queries
           submitted or monitored through those applications. For example: <ul>
             <li> Press <systemoutput>^C</systemoutput> in
                 <cmdname>impala-shell</cmdname>. </li>
             <li> Click <b>Cancel</b> from the <b>Watch</b>page in Hue. </li>
           </ul>
         </p>
       </conbody>
     </concept>

   </concept>

 </concept>
	<?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 rev="1.2.1" id="timeouts">

	<title>Setting Timeout Periods for Daemons, Queries, and Sessions</title>

	<titlealts audience="PDF">

	<navtitle>Setting Timeouts</navtitle>

	</titlealts>

	<prolog>
	<metadata>
	<data name="Category" value="Impala"/>
	<data name="Category" value="Administrators"/>
	<data name="Category" value="Scheduling"/>
	<data name="Category" value="Scalability"/>
	</metadata>
	</prolog>

	<conbody>

	<p>
	Depending on how busy your <keyword keyref="distro"/> cluster is, you might increase or decrease various timeout
	values. Increase timeouts if Impala is cancelling operations prematurely, when the system
	is responding slower than usual but the operations are still successful if given extra
	time. Decrease timeouts if operations are idle or hanging for long periods, and the idle
	or hung operations are consuming resources and reducing concurrency.
	</p>

	<p outputclass="toc inpage"/>

	</conbody>

	<concept id="statestore_timeout">

	<title>Increasing the Statestore Timeout</title>

	<conbody>

	<p rev="IMP-1210">
	If you have an extensive Impala schema, for example with hundreds of databases, tens of
	thousands of tables, and so on, you might encounter timeout errors during startup as the
	Impala catalog service broadcasts metadata to all the Impala nodes using the statestore
	service. To avoid such timeout errors on startup, increase the statestore timeout value
	from its default of 10 seconds. Specify the timeout value using the
	<codeph>-statestore_subscriber_timeout_seconds</codeph> option for the statestore
	service, using the configuration instructions in
	<xref href="impala_config_options.xml#config_options"/>. The symptom of this problem is
	messages in the <codeph>impalad</codeph> log such as:
	</p>

	<codeblock>Connection with state-store lost
	Trying to re-register with state-store</codeblock>

	<p>
	See <xref href="impala_scalability.xml#statestore_scalability"/> for more details about
	statestore operation and settings on clusters with a large number of Impala-related
	objects such as tables and partitions.
	</p>

	</conbody>

	</concept>

	<concept id="impalad_timeout">

	<title>Setting the Idle Query and Idle Session Timeouts for impalad</title>

	<conbody>

	<p>
	To keep long-running queries or idle sessions from tying up cluster resources, you can
	set timeout intervals for both individual queries, and entire sessions.
	</p>

	<note conref="../shared/impala_common.xml#common/timeout_clock_blurb"/>

	<p>
	Use the following startup options for the <cmdname>impalad</cmdname>
	daemon to specify timeout values:
	</p>

	<ul>
	<li><codeph>--idle_query_timeout</codeph>
	<p>
	Specifies the time in
	seconds after which an idle query is cancelled. This could be a
	query whose results were all fetched but was never closed, or one
	whose results were partially fetched and then the client program
	stopped requesting further results. This condition is most likely to
	occur in a client program using the JDBC or ODBC interfaces, rather
	than in the interactive <cmdname>impala-shell</cmdname> interpreter.
	Once a query is cancelled, the client program cannot retrieve any
	further results from the query.
	</p>
	<p rev="2.0.0">
	You can reduce
	the idle query timeout by using the <codeph>QUERY_TIMEOUT_S</codeph>
	query option. Any non-zero value specified for the
	<codeph>--idle_query_timeout</codeph> startup option serves as an
	upper limit for the <codeph>QUERY_TIMEOUT_S</codeph> query option.
	See <xref href="impala_query_timeout_s.xml#query_timeout_s"/> about
	the query option.
	</p>
	<p rev="2.0.0">A zero value for
	<codeph>--idle_query_timeout</codeph> disables query timeouts.
	</p>
	<p>
	Cancelled queries remain in the open state but use only the
	minimal resources.
	</p>
	</li>

	<li><codeph>--idle_session_timeout</codeph>
	<p>
	Specifies the time in
	seconds after which an idle session expires. A session is idle when
	no activity is occurring for any of the queries in that session, and
	the session has not started any new queries. Once a session is
	expired, you cannot issue any new query requests to it. The session
	remains open, but the only operation you can perform is to close it.
	</p>
	<p>
	The default value of 0 specifies sessions never
	expire.
	</p>
	<p rev="2.12.0">
	You can override the
	<codeph>--idle_session_timeout</codeph> value with the <xref
	href="impala_idle_session_timeout.xml#idle_session_timeout"/> at
	the session level.
	</p>
	</li>
	</ul>

	<p>
	For instructions on changing <cmdname>impalad</cmdname> startup options, see
	<xref href="impala_config_options.xml#config_options"/>.
	</p>

	<note>
	<p rev="IMPALA-5108">
	Impala checks periodically for idle sessions and queries
	to cancel. The actual idle time before cancellation might be up to 50% greater than
	the specified configuration setting. For example, if the timeout setting was 60, the
	session or query might be cancelled after being idle between 60 and 90 seconds.
	</p>
	</note>

	</conbody>

	</concept>
	<concept id="concept_rfy_jl1_rx">
	<title>Setting Timeout and Retries for Thrift Connections to the Backend
	Client</title>
	<conbody>
	<p>Impala connections to the backend client are subject to failure in
	cases when the network is momentarily overloaded. To avoid failed
	queries due to transient network problems, you can configure the number
	of Thrift connection retries using the following option: </p>
	<ul id="ul_bj3_ql1_rx">
	<li>The <codeph>--backend_client_connection_num_retries</codeph> option
	specifies the number of times Impala will try connecting to the
	backend client after the first connection attempt fails. By default,
	<cmdname>impalad</cmdname> will attempt three re-connections before
	it returns a failure. </li>
	</ul>
	<p>You can configure timeouts for sending and receiving data from the
	backend client. Therefore, if for some reason a query hangs, instead of
	waiting indefinitely for a response, Impala will terminate the
	connection after a configurable timeout.</p>
	<ul id="ul_vm2_2v1_rx">
	<li>The <codeph>--backend_client_rpc_timeout_ms</codeph> option can be
	used to specify the number of milliseconds Impala should wait for a
	response from the backend client before it terminates the connection
	and signals a failure. The default value for this property is 300000
	milliseconds, or 5 minutes. </li>
	</ul>
	</conbody>
	</concept>

	<concept id="cancel_query">

	<title>Cancelling a Query</title>

	<conbody>
	<p> Occasionally, an Impala query might run for an unexpectedly long time,
	tying up resources in the cluster. This section describes the options to
	terminate such runaway queries.</p>
	</conbody>
	<concept id="cancel_query_with_query_option">
	<title>Setting a Time Limit on Query Execution</title>
	<conbody>
	<p>An Impala administrator can set a default value of the
	<codeph>EXEC_TIME_LIMIT_S</codeph> query option for a resource pool.
	If a user accidentally runs a large query that executes for longer
	than the limit, it will be automatically terminated after the time
	limit expires to free up resources. </p>
	<p>You can override the default value per query or per session if you do
	not want to apply the default <codeph>EXEC_TIME_LIMIT_S</codeph> value
	to a specific query or a session. See <xref
	href="impala_exec_time_limit_s.xml#exec_time_limit_s"/> for the
	details of the query option.</p>
	</conbody>
	</concept>
	<concept id="cancel_query_in_webUI">
	<title>Interactively Cancelling a Query </title>
	<conbody>
	<p> You can cancel the query explicitly, independent of the timeout
	period, by going into the web UI for the <cmdname>impalad</cmdname>
	host (on port 25000 by default), and using the link on the
	<codeph>/queries</codeph> tab to cancel the running query. </p>
	<p> Various client applications let you interactively cancel queries
	submitted or monitored through those applications. For example: <ul>
	<li> Press <systemoutput>^C</systemoutput> in
	<cmdname>impala-shell</cmdname>. </li>
	<li> Click <b>Cancel</b> from the <b>Watch</b>page in Hue. </li>
	</ul>
	</p>
	</conbody>
	</concept>

	</concept>

	</concept>