Re: Questions about Core Data and SQLite
Re: Questions about Core Data and SQLite
- Subject: Re: Questions about Core Data and SQLite
- From: Chris Hanson <email@hidden>
- Date: Mon, 14 Jul 2008 21:19:05 -0700
On Jul 14, 2008, at 9:08 PM, Jens Alfke wrote:
On 14 Jul '08, at 6:05 PM, Steve Steinitz wrote:
I use a little gigabit Thecus Network Drive which is just about as
fast as using the internal disk. Humorously, my database currently
fits in the Thecus' cache so it runs even faster.
The scalability problem isn't the I/O speed, but the fact that the
clients are using filesystem locks for mutual exclusion, and polling
the lock for scheduling. Typically if the file is locked the process
will wait a few seconds, then try again. As the percentage of busy
time of the file increases, the delay to access it gets unacceptably
long.
On filesystems that support them properly, SQLite will use byte-range
locks which can provide much better performance for this type of
situation than full-file locks.
That's part of why it's important that every user of a SQLite database
that's on a networked filesystem access it through a compatible
mechanism: If the clients use different protocols to access the file,
depending on the server implementation, they may not actually share
lock state.
This is fundamentally the same as putting a FileMaker or Access
database on a file server and having multiple users open it.
-- Chris
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