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https://issues.apache.org/jira/browse/COUCHDB-487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12748365#action_12748365
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Robert Newson commented on COUCHDB-487:
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That's a fair concern. My preferred fix is to use multiple files that can be
compacted/obsoleted separately, which makes it non-blocking even under heavy nd
continuous writing.
I was aware of the multi-pass nature of compaction when I wrote the patch,
which is why it doesn't kick in at all unless it tries and fails to switch over
to the compact file. I can modify the patch to only make write_available=false
if the seq delta is below a configurable threshold, which is a nice change
anyway, and the default can be 0, which is today's behavior.
> Pause write requests to allow compaction to complete
> ----------------------------------------------------
>
> Key: COUCHDB-487
> URL: https://issues.apache.org/jira/browse/COUCHDB-487
> Project: CouchDB
> Issue Type: Improvement
> Components: Database Core
> Reporter: Robert Newson
> Attachments: block_writes_after_end_of_compaction.patch
>
>
> Continuous writes will currently indefinitely prevent the compaction process
> from flipping over to the .compact file.
> Here's a small patch that adds a new db flag called 'write_available' which
> becomes false the first time compaction completes but fails to flip over
> because of concurrent writes. Subsequent calls to update_docs then sleep for
> 1/2 a second and throw retry.
> I ran 'ab -p json -n 1000000 http://localhost:5984/db1' in one window.
> Without this patch, I get a long sequence of;
> [info] [<0.64.0>] Compaction file still behind main file (update seq=1848.
> compact update seq=1845). Retrying.
> and compaction never completes.
> With the patch, I get this;
> [info] [<0.369.0>] 127.0.0.1 - - 'POST' /db1 201
> [info] [<0.65.0>] Compaction file still behind main file (update seq=2140.
> compact update seq=2092). Retrying.
> [info] [<0.65.0>] Blocking writes to complete compaction.
> [info] [<0.65.0>] Compaction for db "db1" completed.
> [info] [<0.370.0>] 127.0.0.1 - - 'POST' /db1 201
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