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https://issues.apache.org/jira/browse/JCR-1820?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Marcel Reutegger updated JCR-1820:
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Attachment: JCR-1820.patch
The proposed patch performs a check on the number of nodes that get added by
the update and prepares an index reader when the number is higher than the
buffer size. This should be a reasonable threshold because it will only trigger
a writer flush when it is inevitable anyway.
> Ensure queries are not blocked during large updates
> ---------------------------------------------------
>
> Key: JCR-1820
> URL: https://issues.apache.org/jira/browse/JCR-1820
> Project: Jackrabbit
> Issue Type: Improvement
> Components: jackrabbit-core
> Reporter: Marcel Reutegger
> Priority: Minor
> Attachments: JCR-1820.patch
>
>
> The index currently guarantees that long running queries do not block
> updates. In addition a query *may* run during an update, but there is not
> guarantee because it depends on the availability of an index reader being
> available when the update starts. The index reader is invalidated at the end
> of the update, which will force the creation of a new index reader when the
> next query is executed.
> Consider the following scenario:
> 1) update index -> transaction id T1
> 2) potential index reader is invalidated
> 3) execute query -> creates index reader R1, which includes changes up to T1
> 4) update index -> transaction id T2
> 5) index reader R1 is invalidated
> 6) update index (large transaction) -> transaction id T3
> 7) while previous update is running execute query -> thread is blocked
> because no reader is available
> The improvement should detect the large transaction and prepare an index
> reader for potential queries during the update. That is, 6) should be split
> into:
> 6a) detect large transaction and prepare index reader R2, which includes
> changes up to T2
> 6b) update index -> transaction id T3
> While the update is running a query will use index reader R2.
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