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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