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From "Adam Kocoloski (JIRA)" <j...@apache.org>
Subject [jira] Created: (COUCHDB-568) When delayed_commits = true, keep updated btree nodes in memory until the commit
Date Wed, 11 Nov 2009 16:09:39 GMT
When delayed_commits = true, keep updated btree nodes in memory until the commit
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                 Key: COUCHDB-568
                 URL: https://issues.apache.org/jira/browse/COUCHDB-568
             Project: CouchDB
          Issue Type: Improvement
    Affects Versions: 0.10
            Reporter: Adam Kocoloski


rnewson reported on IRC that the new batch=ok implementation results in significantly larger
overhead in the .couch files.  This makes sense; the old batch mode waited 1 second before
saving, but the new implementation just updates the doc asynchronously.  With fast hardware
and moderate write rates it's likely that each document is being written separately.

The overhead presumably arises from frequently updated btree inner nodes being written to
disk many times over.  I'm interested in exploring a modification of the delayed_commits mode
whereby the updated btree nodes are not actually written to disk immediately, but are instead
held in memory until the commit.  I'd like to think that this will result in more compact
files without any decrease in durability.  New read requests would still be able to access
these in-memory nodes.

I realize the notion that updates go directly to disk is baked pretty deeply into couch_btree,
but I still thought this was worth bringing up to a wider audience.

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