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https://issues.apache.org/jira/browse/LUCENE-8542?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16704304#comment-16704304
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Lucene/Solr QA commented on LUCENE-8542:
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| (/) *{color:green}+1 overall{color}* |
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|| Vote || Subsystem || Runtime || Comment ||
|| || || || {color:brown} Prechecks {color} ||
| {color:green}+1{color} | {color:green} test4tests {color} | {color:green}  0m 
 0s{color} | {color:green} The patch appears to include 1 new or modified test 
files. {color} |
|| || || || {color:brown} master Compile Tests {color} ||
| {color:green}+1{color} | {color:green} compile {color} | {color:green}  1m 
38s{color} | {color:green} master passed {color} |
|| || || || {color:brown} Patch Compile Tests {color} ||
| {color:green}+1{color} | {color:green} compile {color} | {color:green}  0m 
51s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} javac {color} | {color:green}  0m 
51s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} Release audit (RAT) {color} | 
{color:green}  0m 30s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} Check forbidden APIs {color} | 
{color:green}  0m 20s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} Validate source patterns {color} | 
{color:green}  0m 20s{color} | {color:green} the patch passed {color} |
|| || || || {color:brown} Other Tests {color} ||
| {color:green}+1{color} | {color:green} unit {color} | {color:green} 30m 
12s{color} | {color:green} core in the patch passed. {color} |
| {color:green}+1{color} | {color:green} unit {color} | {color:green}  3m 
10s{color} | {color:green} facet in the patch passed. {color} |
| {color:black}{color} | {color:black} {color} | {color:black} 40m 30s{color} | 
{color:black} {color} |
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|| Subsystem || Report/Notes ||
| JIRA Issue | LUCENE-8542 |
| JIRA Patch URL | 
https://issues.apache.org/jira/secure/attachment/12950019/LUCENE-8542.patch |
| Optional Tests |  compile  javac  unit  ratsources  checkforbiddenapis  
validatesourcepatterns  |
| uname | Linux lucene2-us-west.apache.org 4.4.0-112-generic #135-Ubuntu SMP 
Fri Jan 19 11:48:36 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux |
| Build tool | ant |
| Personality | 
/home/jenkins/jenkins-slave/workspace/PreCommit-LUCENE-Build/sourcedir/dev-tools/test-patch/lucene-solr-yetus-personality.sh
 |
| git revision | master / 75b1831 |
| ant | version: Apache Ant(TM) version 1.9.6 compiled on July 20 2018 |
| Default Java | 1.8.0_191 |
|  Test Results | 
https://builds.apache.org/job/PreCommit-LUCENE-Build/127/testReport/ |
| modules | C: lucene lucene/core lucene/facet U: lucene |
| Console output | 
https://builds.apache.org/job/PreCommit-LUCENE-Build/127/console |
| Powered by | Apache Yetus 0.7.0   http://yetus.apache.org |


This message was automatically generated.



> Provide the LeafSlice to CollectorManager.newCollector to save memory on 
> small index slices
> -------------------------------------------------------------------------------------------
>
>                 Key: LUCENE-8542
>                 URL: https://issues.apache.org/jira/browse/LUCENE-8542
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: core/search
>            Reporter: Christoph Kaser
>            Priority: Minor
>         Attachments: LUCENE-8542.patch
>
>
> I have an index consisting of 44 million documents spread across 60 segments. 
> When I run a query against this index with a huge number of results requested 
> (e.g. 5 million), this query uses more than 5 GB of heap if the IndexSearch 
> was configured to use an ExecutorService.
> (I know this kind of query is fairly unusual and it would be better to use 
> paging and searchAfter, but our architecture does not allow this at the 
> moment.)
> The reason for the huge memory requirement is that the search [will create a 
> TopScoreDocCollector for each 
> segment|https://github.com/apache/lucene-solr/blob/master/lucene/core/src/java/org/apache/lucene/search/IndexSearcher.java#L404],
>  each one with numHits = 5 million. This is fine for the large segments, but 
> many of those segments are fairly small and only contain several thousand 
> documents. This wastes a huge amount of memory for queries with large values 
> of numHits on indices with many segments.
> Therefore, I propose to change the CollectorManager - interface in the 
> following way:
>  * change the method newCollector to accept a parameter LeafSlice that can be 
> used to determine the total count of documents in the LeafSlice
>  * Maybe, in order to remain backwards compatible, it would be possible to 
> introduce this as a new method with a default implementation that calls the 
> old method - otherwise, it probably has to wait for Lucene 8?
>  * This can then be used to cap numHits for each TopScoreDocCollector to the 
> leafslice-size.
> If this is something that would make sense for you, I can try to provide a 
> patch.



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