Re: [Dovecot] How to get rid of locks

On Sat, 2007-04-07 at 22:30 +0300, Timo Sirainen wrote:

I just figured out that O_APPEND is pretty great. If the operating
system updates seek position after writing to a file opened with
O_APPEND, writes to Dovecot's transaction log file can be made
lockless.

Well, almost. Log rotation isn't possible without some sort of locking. But the locks could still be reduced:

• Normally keep the .log file read-locked all the time (multiple processes can have it read-locked)
• Write to it with O_APPEND
• If you notice that the log is going to be rotated soon, drop the read lock and acquire it only for the duration of appends
• When the log is wanted to be rotated, try to get a write-lock. If it fails, try again later. If it succeeds, it's safe to rotate the log.