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https://issues.apache.org/jira/browse/OAK-1032?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jukka Zitting resolved OAK-1032.
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Resolution: Fixed
Fix Version/s: 0.11
Assignee: Jukka Zitting
There is now only one SegmentWriter.
> SegmentMK: One SegmentWriter per SegmentNodeStore
> -------------------------------------------------
>
> Key: OAK-1032
> URL: https://issues.apache.org/jira/browse/OAK-1032
> Project: Jackrabbit Oak
> Issue Type: Sub-task
> Components: core
> Reporter: Jukka Zitting
> Assignee: Jukka Zitting
> Priority: Minor
> Fix For: 0.11
>
>
> Currently each SegmentNodeStoreBranch (and thus Root) instance has it's own
> SegmentWriter that it uses to construct new segments. This allows maximum
> write concurrency as there's no need for any synchronization at the
> SegmentWriter level.
> The downside of this solution is that the resulting segments are often very
> small (< 100 bytes), which increases write overhead (in TarMK each segment
> needs at least 1kB of disk space) and reduces locality of reference (related
> content gets scattered across many segments). And concurrent write throughput
> is in any case constrained when more than one writer is updating the same
> journal.
> Thus I think it would be good to instead have just one SegmentWriter per
> SegmentNodeStore and have all branches use that shared writer. This requires
> synchronization when writing individual records, and can thus lead to extra
> contention, but since records are fine-grained and all record writes happen
> in memory, the amount of contention should be fairly small for normal
> workloads (and for truly heavy concurrent writing, we'd in any case be using
> multiple processes across many cluster nodes, in which case this limit
> wouldn't apply).
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