do a non-blocking file:sync
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Key: COUCHDB-767
URL: https://issues.apache.org/jira/browse/COUCHDB-767
Project: CouchDB
Issue Type: Improvement
Components: Database Core
Affects Versions: 0.11
Reporter: Adam Kocoloski
Fix For: 1.1
I've been taking a close look at couch_file performance in our production
systems. One of things I've noticed is that reads are occasionally blocked for
a long time by a slow call to file:sync. I think this is unnecessary. I think
we could do something like
handle_call(sync, From, #file{name=Name}=File) ->
spawn_link(fun() -> sync_file(Name, From) end),
{noreply, File};
and then
sync_file(Name, From) ->
{ok, Fd} = file:open(Name, [read, raw]),
gen_server:reply(From, file:sync(Fd)),
file:close(Fd).
Does anyone see a downside to this? Individual clients of couch_file still see
exactly the same behavior as before, only readers are not blocked by syncs
initiated in the db_updater process. When data needs to be flushed file:sync
is _much_ slower than spawning a local process and opening the file again --
in the neighborhood of 1000x slower even on Linux with its less-than-durable
use of vanilla fsync.
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