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Re: Checkpoint less frequently

From: Branko Čibej <brane_at_xbc.nu>
Date: 2003-02-21 19:03:28 CET

Greg Hudson wrote:

>On Fri, 2003-02-21 at 12:52, Branko Čibej wrote:
>>You don't have to stop any servers, or anythng. Each server only has to
>>ask the monitor if it may open the database, and to notify it when it
>>closes it. When the monitor detects a crashed process, it starts denying
>>access to the database until all other processes have backed out, runs
>>recovery, then allows access again.
>>At least, that's the general idea.
>That doesn't seem very general.
> Process A opens the database
> Process A acquires many fine locks
> Process B opens the database
> Process A crashes
>Process B is just as likely to hit a stale lock and hang as if it had
>opened the database after the crash.
So we wait for a bit, then kill it. We know which processes were active
(i.e., fiddling with the database) at the time of the crash.

Now it's possible that there's another way to solve this problem:
setting the locl timeout. A process will only block forever on a stale
lock _unless_ a timeout has been set (say, in the DB_CONFIG file). Some
time ago when I was testing different ways to avoid the wedged
DB/blocked process problem, I tried this method and it worked within my
limited test cases. But I don't uderstand it well enough, nor have I
stressed it enough, to be ble to say whether this is an acceptable
solution or not.

Brane Čibej   <brane_at_xbc.nu>   http://www.xbc.nu/brane/
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Received on Fri Feb 21 19:04:11 2003

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