Pause write requests to allow compaction to complete
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                 Key: COUCHDB-487
                 URL: https://issues.apache.org/jira/browse/COUCHDB-487
             Project: CouchDB
          Issue Type: Improvement
          Components: Database Core
            Reporter: Robert Newson
         Attachments: 0001-block-writes-at-completion-of-compaction-to-allow-sw.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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