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https://issues.apache.org/jira/browse/LUCENE-9432?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17159213#comment-17159213
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Uwe Schindler edited comment on LUCENE-9432 at 7/16/20, 1:27 PM:
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Hi,
I checked the patch. A linkedlist is in most cases a bad idea, because it does
not allow performant index based access - and that is what is used here. I
don't fully understand the code, but a linked list is a bad choice for this
access pattern, as LinkedList.get() involves linear scan!
The problem you see here is more related to the fact that the array is of zero
size initially and Array.oversize() behaves bad there if initial size is too
small (many copies of small arrays). I'd siply replace the whole thing by an
ArrayList with suitable initial size. If you want a real stack-based behaviour
(push/pop), a better replacement would be ArrayDeque implementing the Deque
interface.
So in short: Either replace by a Deque (fully using the Deque interface
including push/pop and corresponding iterators) or use an ArrayList. A
LinkedList is a bad choice as it might save some copy costs, but it brings a
huge overhead with linear scans and also lots of garbage on heap.
was (Author: thetaphi):
Hi,
I checked the patch. A linkedlist is in most cases a bad idea, because it does
not allow performant index based access - and that is what is used here. I
don't fully understand the code, but a linked list is a bad choice for this
access pattern, as LinkedList.get() involves linear scan!
The problem you see here is more related to the fact that the array is of zero
size initially. I'd siply replace the whole thing by an ArrayList. If you want
a real stack-based behaviour (push/pop), a better replacement would be
ArrayDeque implementing the Deque interface.
So in short: Either replace by a Deque (fully using the Deque interface
including push/pop and corresponding iterators) or use an ArrayList. A
LinkedList is a bad choice as it might save some copy costs, but it brings a
huge overhead with linear scans and also lots of garbage on heap.
> Use LinkedList instead of manual array re-sizing for better throughput.
> -----------------------------------------------------------------------
>
> Key: LUCENE-9432
> URL: https://issues.apache.org/jira/browse/LUCENE-9432
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/codecs
> Reporter: Mohammad Sadiq
> Priority: Minor
> Labels: patch-available, performance, pull-request-available
> Attachments: LUCENE-9432.patch
>
>
> I observed that using {{LinkedList}} instead of manually re-sizing and
> copying {{SegmentTermEnumFrame}}s improves red-line QPS. Does it make sense
> to include this?
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