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https://issues.apache.org/jira/browse/COUCHDB-786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12876305#action_12876305
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Adam Kocoloski commented on COUCHDB-786:
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I'm worried about the interaction of this patch with COUCHDB-767. That issue
contains a patch which causes couch_file to spawn a worker process to sync the
file. The idea behind COUCHDB-767 is that reads can proceed even while the
file is being synced.
It seems that this patch would have the opposite effect -- all readers would be
blocked, not just while a file is synced, but while the header is being written
(which typically involves 2 syncs).
Perhaps it would be a good idea to combine the strategies from both issues, and
spawn a function to do the sync-write-sync dance for write_header? The
challenge is that #file.eof needs to be updated when the header is written,
which is not the case for a simple sync.
> Make fewer gen_server calls to fsync the db header
> --------------------------------------------------
>
> Key: COUCHDB-786
> URL: https://issues.apache.org/jira/browse/COUCHDB-786
> Project: CouchDB
> Issue Type: Improvement
> Components: Database Core
> Affects Versions: 0.10.2, 0.11
> Reporter: Randall Leeds
> Fix For: 0.12
>
> Attachments: 0001-db-header-fsync-with-fewer-gen_server-calls.patch
>
>
> Currently the couch_db_updater process is responsible for calling
> couch_file:sync based on the fsync options when the db header is written.
> Instead, this patch just passes the fsync options down to couch_file so that
> writing the header can always be performed with a single gen_server call.
> Writes are serialized through couch_db_updater but reads can have high
> concurrency. This patch should boost write performance when the message queue
> on couch_file is long.
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