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https://issues.apache.org/jira/browse/SOLR-15301?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17423179#comment-17423179
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Andras Salamon commented on SOLR-15301:
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Asking only for specific metrics instead of all the metrics is a good practice,
but sometimes clients ask for all the possible metrics. And if someone asks for
three index size metrics (for whatever reason), it is not too good to repeat
the index size calculation.
My first idea was also to use a timestamp and some deadline for the expiration
but choose ThreadLocal because of two reasons:
* I was not able to find a good deadline. It depends on the speed of the index
size calculation, and the frequency of the metrics call, which is different for
each scenario. If I hardwire one second and the index size calculation is
slower it will repeat the calculations. The slower the calculation the more
likely we will repeat.
* Without this commit (or with the timestamp expiration solution) the values
returned by a single metrics call are not consistent. Right now we calculate
the index size three times, and the three calculations might return different
values. So now it's possible that we return the raw size 100000 (byes) and the
human readable for 200Kb. The ThreadLocal ensures that the values returned in a
single call are consistent.
> Eliminate repetitive index size calculation for Solr metrics
> ------------------------------------------------------------
>
> Key: SOLR-15301
> URL: https://issues.apache.org/jira/browse/SOLR-15301
> Project: Solr
> Issue Type: Improvement
> Components: metrics
> Reporter: Andras Salamon
> Assignee: Andras Salamon
> Priority: Minor
> Fix For: main (9.0)
>
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> During metrics calculation Solr asks for core indexSize three times. Twice in
> SolrCore and once in ReplicationHandler. It slows down metrics calculation
> and it is also possible that these three reported values are not exactly the
> same if size changes during calculation.
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