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https://issues.apache.org/jira/browse/BOOKKEEPER-963?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15681615#comment-15681615
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Matteo Merli commented on BOOKKEEPER-963:
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Yes, typically we've seen the bottleneck for writes to a single bookie resides
in the Journal.
When writing batched entries of 128KB we can write up to 130 MB /sec on a
single SSD (with RAID-1 mirroring).
With SSD, it's also to be noted that maximum performance is achievable by
having multiple threads doing sequential writes in different disk blocks.
By having multiple journals we can extend the write-throughput of a single
bookie, with either more disks dedicated to journal or more journals on the
same disk device.
> Allow to use multiple journals in bookie
> ----------------------------------------
>
> Key: BOOKKEEPER-963
> URL: https://issues.apache.org/jira/browse/BOOKKEEPER-963
> Project: Bookkeeper
> Issue Type: Improvement
> Reporter: Matteo Merli
> Assignee: Matteo Merli
> Fix For: 4.5.0
>
>
> By configuring multiple journals, we can take advantage of the IO of multiple
> disks to increase the write throughput of a single bookie.
> Each journal will have its own journal and sync threads and writes will be
> assigned to a particular journal by hashing on the ledger id.
> In addition to using multiple physical disks, there can improvements even by
> using multiple journal on a single SSD device, because these disks can handle
> well multiple concurrent writes in different blocks of the disk.
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