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Message-ID: <51A905DC.6020109@etr-usa.com>
Date: Fri, 31 May 2013 14:19:40 -0600
From: Warren Young <warren@etr-usa.com>
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To: cygwin@cygwin.com
Subject: Re: sqlite3: bug with monotone
References: <51A6B6EB.6050309@users.sourceforge.net> <loom.20130530T122354-144@post.gmane.org> <51A7862F.1070507@etr-usa.com> <51A7D47E.3050502@users.sourceforge.net> <51A7F547.6020509@etr-usa.com> <20130531092228.GB30659@calimero.vinschen.de> <51A900EF.2020606@etr-usa.com>
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On 5/31/2013 13:58, Warren Young wrote:
>
> The SQLite code prefers POSIX advisory locks, but it can fall back to
> BSD locks if it has to.

Just to clarify, when I say "POSIX locks" I always mean new style 
fcntl() locks.  There are no calls to lockf() in sqlite3.c.

> I'm not sure why it doesn't just
> blindly try the lock.

On reflection, I'm sure it has something to do with maintaining high 
concurrency.  If it knows its near-future DB file write is going to get 
blocked, it can choose to do something else while the existing DB lock 
holders finish.

By contrast, SQLite's flock() based locking is documented as being much 
more brute-force, resulting in much lower concurrency.

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