[COUCHDB-487] Pause write requests to allow compaction to complete

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Component/s: Database Core
• Skill Level: Committers Level (Medium to Hard)
• Assignee: Unassigned
• Reporter: Robert Newson
• Created: 27/Aug/09 08:50
• Updated: 02/Sep/18 06:26
• Resolved: 02/Sep/18 06:26

Description

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