[jira] [Commented] (LUCENE-7235) Avoid taking the lock in LRUQueryCache when not necessary

["Robert Muir (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-7235?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15251867#comment-15251867 ] 

Robert Muir commented on LUCENE-7235:
-------------------------------------

+1.

I think we should also consider explicitly disabling the cache in tiny cases like MemoryIndex?

> Avoid taking the lock in LRUQueryCache when not necessary
> ---------------------------------------------------------
>
>                 Key: LUCENE-7235
>                 URL: https://issues.apache.org/jira/browse/LUCENE-7235
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Adrien Grand
>            Assignee: Adrien Grand
>            Priority: Minor
>         Attachments: LUCENE-7235.patch
>
>
> LRUQueryCache's CachingWeightWrapper works this way:
>  - first it looks up the cache to see if there is an entry for the query in the current leaf
>  - if yes, it returns it
>  - otherwise it checks whether the query should be cached on this leaf
>  - if yes, it builds a cache entry and returns it
>  - otherwise it returns a scorer built from the wrapped weight
> The potential issue is that this first step always takes the lock, and I have seen a couple cases where indices were small and/or queries were very cheap and this showed up as a bottleneck. On the other hand, we have checks in step 3 that tell the cache to not cache on a particular segment regardless of the query. So I would like to move that part before 1 so that we do not even take the lock in that case.
> For instance right now we require that segments have at least 10k documents and 3% of all docs in the index to be cached. I just looked at a random index that contains 1.7m documents, and only 4 segments out of 29 met this criterion (yet they contain 1.1m documents: 65% of the total index size). So in the case of that index, we would take the lock 7x less often.



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)

---------------------------------------------------------------------
To unsubscribe, e-mail: dev-unsubscribe@lucene.apache.org
For additional commands, e-mail: dev-help@lucene.apache.org