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https://issues.apache.org/jira/browse/COUCHDB-2097?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14052891#comment-14052891
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Paul Joseph Davis commented on COUCHDB-2097:
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> 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 is incorrect. Reads don't go through the couch_db_updater process. You are
right that reads and writes are going through the same fd now though. As to why
the change uses the fd process instead of the db process, couch_file can
outlive the db updater process for clients that have long requests. Streaming
large views when the number of open dbs is near max_dbs_open for instance.
> I would be interested by measuring the difference on that particular part,
> not on the overall performance of the db.
Which particular part? two vs one fd? Mike Wallace did that and showed that the
single fd version was considerably slower which we would expect. The changes
that this ticket was concerned with involve the entire change set which
necessarily includes the changes to couch_server.
> 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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