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https://issues.apache.org/jira/browse/COUCHDB-2097?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14052889#comment-14052889
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Benoit Chesneau commented on COUCHDB-2097:
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This is not about having 2 files process or not. With the change everything is
now serialised, first in the updater process and then in the file process. So
with this changes read and writes are now waiting in the same queue. 2 times.
This design is already a problem and the one we should skip in a database
generally. I already showed on a single node that long writes (with large docs
or bulk updates) have a direct impact on reads (i will work on a test case to
measure it). Latest rcouch have reverted this change and is quite more stable
on a standalone node.Imo this is a direct regression compared to the old
situation where multiple reads can be done distinctly from writes.
I know that this changes was done to remove the reference counting. However I
don't see why this should be done by only relying on 1 file process. Why not a
database process? In any case I think that removing or improving reference
counting shouldn't have an impact on read//writes. The current patch may
improve the overall performances in the database but it adds a bottleneck by
doing it.
I would be interested by measuring the difference on that particular part, not
on the overall performance of the db. So we can make a rational decisions
pondering advantages of one against the other and make sure most scenarios are
taken in consideration.
> Avoid performance regression with a single fd
> ---------------------------------------------
>
> Key: COUCHDB-2097
> URL: https://issues.apache.org/jira/browse/COUCHDB-2097
> Project: CouchDB
> Issue Type: Improvement
> Security Level: public(Regular issues)
> Components: BigCouch
> Reporter: Paul Joseph Davis
> Labels: release
> Attachments: mike-wallace-fd-benchmarks.txt
>
>
> Part of one of our large enhancements required that we remove a CouchDB
> performance optimization on having two file handles to each .couch file. We
> need to make sure that this doesn't negatively impact performance.
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